Line Intensities in the ν 6 Fundamental Band of CH 3 Br at 10 µm

Transcription

1 Journal of Molecular Spectroscopy 216, (2002) doi: /jmsp Line Intensities in the ν 6 Fundamental Band of CH 3 Br at 10 µm E. Brunetaud, I. Kleiner, and N. Lacome Laboratoire de Dynamique, Interactions et Réactivité/Spectrochimie Moléculaire, Université Pierre et Marie Curie, UMR CNRS 7075, Case Courrier 49, 4 Place Jussieu, Paris Cedex 05, France; and Laboratoire de Photophysique Moléculaire, Université Paris Sud, UPR CNRS 3361, Bâtiment 350, Orsay Cedex, France Received February 14, 2002; in revised form June 21, 2002 Fourier transform spectra have been obtained at 296 K at a resolution of or cm 1 depending on the pressure range. Line positions and intensities of CH 3 79 Br and CH 3 81 Br belonging to the fundamental band ν 6 were measured and analyzed between 890 and 1080 cm 1. A total of 2896 (2838) line positions with J 60 and K 6 was fitted with a root-mean-square deviation of ( ) cm 1 for CH 3 79 Br and CH 3 81 Br, respectively, within the experimental accuracy. The fit to 316 (312) measured intensities yielded values of the dipole moment derivatives of both isotopes with a standard deviation of 5% to be compared to an experimental uncertainty equal to 6% or better. A prediction of the line positions and intensities has been generated for atmospheric purposes with all lines from 820 to 1120 cm 1 with intensities greater than 10 5 cm 2 atm 1. Key Words: methyl bromide; line positions; intensities; IR absorption. INTRODUCTION Observations of stratospheric bromide species show that bromine is directly involved in the catalytic destruction of ozone in the lower stratosphere. Methyl bromide (CH 3 Br) has been identified as the major contributor to stratospheric bromine and the primary organobromine species in the lower atmosphere. Tropospheric concentrations of CH 3 Br are pptv in the Northern Hemisphere and 8 10 pptv in the Southern Hemisphere (1). Ozone destruction by bromine is more efficient by a factor of 30 to 60 on a per-molecule basis than ozone destruction by chlorine. Therefore, one part per trillion by volume (pptv) of bromide is equivalent to parts per billion by volume (ppbv) of stratospheric chlorine (2). Atmospheric methyl bromide compounds that are involved in stratospheric ozone depletion originate from both natural and anthropogenic sources. The use of methyl bromide as an agricultural fumigant has led to its inclusion in both the Montreal Protocol on Substances that Deplete the Ozone Layer and the U.S. Clean Air Act. We propose to investigate the optimal conditions for a spectroscopic study in situ to follow the evolution of its atmospheric concentration. Therefore, this requires accurate knowledge of spectral parameters and, at the present time, no spectroscopic information (line positions, intensities, and linewidths) on CH 3 Br is available from either the HITRAN (3) or the GEISA (4) database. Studies of trace molecules by IR absorption in the atmosphere may be difficult because their absorption features can be blended by strong absorptions of the major constituents. One of the best candidates for atmospheric remote sensing seems to be the vibrational fundamental band ν 6 located near 954 cm 1, in an atmospheric win- Supplementary data for this article may be found on the journal home page. dow. Many studies of line positions have already been devoted to the analysis of the rovibrational spectra of methyl bromide. Reference (5) presents an extensive review of all works prior to More recent works on the ν 6 band involve microwave and millimeter-wave spectroscopy (6), Doppler free saturation spectroscopy with a CO 2 waveguide laser (7), submillimeterwave spectroscopy (8), submillimeter-wave and infrared laser sideband spectroscopy (9), and laser Stark spectroscopy (10). Chevalier et al. (9) have determined both the upper state, v 6 = 1, and the ground state constants from combined analysis of the infrared and submillimeter-wave data, including also previous experimental data. In 1988, Sakai and Katayama also published a laser Stark spectroscopic study of the 2ν 6 ν 6 hot band of CH 3 Br (10). In that work, the axial rotational constants A 0, D 0 K, and HK 0 in the ground state were determined by analyzing ground state combination differences between K =±3 energy levels. They also improved the v 6 = 1 parameters during the course of their study. In contrast to the extensive number of studies involving line positions, relatively little was done for the intensities in the ν 6 region. Only integrated absorptions measured under lowresolution conditions can be found (11 14). The purpose of the present study is to accurately measure the absolute intensities for the fundamental ν 6 bands of both CH 79 3 Br and CH 81 3 Br isotopes and perform a line-by-line prediction of line positions and intensities of this band. The intensity parameters are derived by analyzing a set of individual line intensities accurately measured by FTIR. The theoretical approach used is a semi-rigid C 3v Hamiltonian for an isolated degenerated band such as ν 6 (15). From the fit of the observed data, values of the dipole moment derivatives dµ/dq 6 are extracted for both isotopes according to a general procedure extensively developed in Ref. (16) /02 $35.00 All rights reserved. 30

2 LINE INTENSITIES OF CH 3 Br AT 10 µm 31 The following sections present the experimental details, the data reduction procedure, the theoretical treatment leading to line intensities data, and the procedure used for extracting the dipole moment derivatives. From the resulting values of the dipole moment derivative a global line-by-line prediction is presented. EXPERIMENTAL DETAILS Two sets of experiments have been carried out in the cm 1 region, one to measure the line positions and another to measure the individual line intensities. All spectra have been recorded with a Bruker IFS 120 Fourier transform spectrometer equipped with a MCT photovoltaic detector, a Ge/KBr beamsplitter, and a Globar source. The whole optical path was under vacuum. The MCT detector was used in conjunction with an optical filter, with a bandpass of cm 1, to minimize the size of the interferogram data files and also to improve the S/N ratio. This filter has been wedged to avoiding interference fringes. The resolutions used ranged from to cm 1. The spectrum at each pressure is the average of 12 spectra, each one integrated for 1 h. Signal-to-noise ratios around 120 : 1 at a resolution of cm 1 were obtained. These S/N ratios are not higher because the band studied was not located at the center of the detector s response curve. Two different cells were used. A direct path cell, 30.0 ± 0.1 cm long, equipped with KCl windows was used for pressures ranging between 5 and 50 Torr. Lower pressure experiments were carried out with a 1-m multipass White-type cell, also with KCl windows. Total optical path length was 415 ± 1 cm. The experimental set-up used in this study was previously described in Ref. (17). All measurements were carried out at room temperature, 296 ± 1 K, and gas pressures are listed in Table 1. During the recording of the TABLE 1 Experimental Conditions Pressure (Torr) Resolution (cm 1 ) White-type Cell (2) (415 cm) (10) (2) (4) (5) (6) (8) (12) cm Cell 5.361(8) (10) (2) (4) (5) (7) Note. Temperature: 296 K. spectra, the temperature was continuously monitored using platinium sondes attached inside the cell. Pressures were measured with capacitive gauges (1, 10, 100 Torr). The sample gas, with bromine under natural abundance, was provided by Fluka and was reported to be 99.5% pure. An additional spectrum of NH 3 obtained with a White-type cell was used to calibrate line positions (with the HITRAN database as standard (3)). DATA REDUCTION Individual line parameters were retrieved from the laboratory spectra using a nonlinear least-squares fitting technique. Each spectrum was compared to a computed synthetic spectrum and the line positions, intensities, and self-broadening widths were adjusted to reduce the differences between the observed and computed spectra. This treatment was done on small intervals of 0.2 cm 1 in the range cm 1. Synthetic spectra were calculated as sums of additive Voigt profiles and no line mixing was introduced. They were then convoluted by an apparatus function which takes into account the finite path difference and the finite entrance aperture (18). This procedure yielded to a set of line positions, intensities, and widths for each pressure. The resulting linewidth data results will be reported in a forthcoming article. For each measured line, an average of line positions and a linear fit of line intensities as a function of pressure was done, giving the frequency in cm 1 and the absolute intensity in cm 2 atm 1. No pressure shifts have been introduced since they could not be observed. The accuracy of the wavenumbers of isolated lines was estimated to be around cm 1. An example of the pressure dependence of line intensities is shown on Fig. 1. Practically, only the spectrum recorded under the lowest pressure, which exhibits the best rotational structure, was individually least-squares fitted. A code was written to perform automatically the treatment of all other spectra at different pressures, as well as the linear fits versus pressure. INTENSITY ANALYSIS The individual absolute intensity I B A (in cm 2 atm 1 at a temperature T ) for a transition between two vibrational rotational states A B is (19) 3 [ ( 8π IA B = 3hc T 0 g A ν B TQ A 1 exp hcν )] B A T kt ( exp hce ) A B µ t Z A 2. [1] kt In [1], = molecules cm 3 is the Loschmidt number at T 0 = K and P = 1 atm; T = 296 K; Q T = for CH 79 3 Br and for CH 81 3 Br are the total partition functions we calculated; ν B A is the

3 32 BRUNETAUD, KLEINER, AND LACOME For the v 6 = 1 degenerate upper state, the diagonal matrix element of the vibration rotation Hamiltonian is (15) v,l, J, K H v,l, J, K = ν 0 + BJ(J + 1) + (A B)K 2 2Aζ Kl D J J 2 (J + 1) 2 D JK J(J + 1)K 2 D K K 4 + H J J 3 (J + 1) 3 + H JK J 2 (J + 1) 2 K 2 + H KJ J(J + 1)K 4 + H K K 6 + η J J(J + 1)Kl + η K K 3 l. [3] One of the l -type off-diagonal matrix elements is also needed in the line position fit: v,l, J, K H v,l ± 2, J, K ± 2 = 2q 2 [J(J + 1) K (K ± 1)] 1/2 [J(J + 1) (K ± 1)(K ± 2)] 1/2. [4] FIG. 1. Pressure dependence: ( ) measured values for the P P 5 (21) line with S 0 = (5.02 ± 0.02) 10 3 cm 2 /atm at 296 K; ( ) measured values for the R P 0 (11) line with S 0 = (9.9 ± 0.1) 10 2 cm 2 /atm at 296 K; ( ) fits. wavenumber of the transition (in cm 1 ); g A and E A are the total degeneracy and the energy of the lower state, respectively; B µ t Z A is the M-reduced transition dipole moment, A and B are the eigenvectors that can be described as linear combination of the zeroorder basis wavefunction v,l, J, K for the lower and the upper state, respectively, c is the speed of light, and h and k represent the Planck and Boltzmann constants, respectively. The knowledge of the eigenvectors is thus required for the fit of the line intensities. To avoid problems related to phase conventions and to the definitions of matrix elements in the intensity fit, we decided to fit the energy parameters. For the ground state, the energy levels are calculated using the parameters from Ref. (10); in this study, in addition to their measured laser Stark data for the 2ν 6 ν 6 and ν 6 bands, previous microwave data (6, 20 22) and IR data (7), as well as ground-state combination differences calculated from the IR ν 4 band (23), were analyzed. The ground state parameters used in the present study are shown for both isotopes in Table 2. They are included as a constraint entry in our fit. The rotational energy for the ground state energy levels may be written E = B 0 J(J + 1) + (A 0 B 0 )K 2 D 0 J J 2 (J + 1) 2 D 0 JK J(J + 1)K 2 D 0 K K 4 + H 0 J J 3 (J + 1) 3 + H 0 JK J 2 (J + 1) 2 K 2 + H 0 KJ J(J + 1)K 4 + H 0 K K 6. [2] The set of programs written by G. Tarrago for C 3v symmetrictop molecules was used to analyze both the line positions and intensities (24). Line assignments of the ν 6 band were first TABLE 2 Molecular Parameters of the ν 6 Band of CH 3 Br (cm 1 ) a CH 3 79 Br CH 3 81 Br ν 6 state ν (1) (1) A (2) (1) B (3) (2) Aζ (3) (2) D J (1) (9) D JK (9) (6) D K (3) 8.778(2) η J (5) 9.417(3) η K (3) 1.206(2) H J [ 1.9] b [ 1.9] b H JK [3.2] b [4.7] b H KJ [1.97] b [1.95] b H K 10 9 [4.1] b [4.6] b q (1) 7.398(1) Ground state c A (21) (11) B (3) (2) D 0 J (2) (1) D 0 JK (4) (2) D 0 K (4) 8.48(2) HJ (4) 1.9(3) HJK (14) 4.7(9) HKJ (2) 1.95(2) HK (20) 4.6(11) a Error in parentheses is one standard deviation in units of the last digit except for the axial ground state constants A 0, D 0 K and H K 0, for which the numbers in parentheses are 2.5 times the standard deviation. b Fixed to the ground state value of Ref. (10). c From Ref. (10).

4 LINE INTENSITIES OF CH 3 Br AT 10 µm 33 performed using the upper state energy parameters published in Ref. (10). Then, for CH 79 3 Br and CH 81 3 Br, some 2896 (2838) line positions with J 60 and K 6 were included in a leastsquares fit and root mean square deviations (rms) of and cm 1, close to the experimental accuracy, were obtained for the 79 and 81 species, respectively. The upper-state energy parameters determined in our fit, using data from the first set of experiments with the 30-cm cell, are given in Table 2. For both isotopes, floating the sixth-order parameters H J, H JK, H KJ, and H K was not found to decrease the rms and therefore we fixed their values to the ground state values. As in Ref. (10), only one l -type term, the q 2 term (in K =±2 l =±2) could be determined. The other l -type term q 1 (in K =±1 l = 2) and the k -type q 3v term (in K =±3) could not be determined in our fit and were constrained to zero. Our fitted v 6 = 1 upper state parameters are in good agreement with those of Ref. (10). Having obtained the eigenvectors for the upper state v 6 = 1, we then fit the line intensities. From the second set of experiments, we selected only intensities of isolated lines with a precision of 6% or better for the analysis. The line intensities corresponding to values higher than J = 60 are too weak to be measured with good accuracy and therefore they are not included in the fit. We used respectively 316 lines for CH 79 3 Br and 312 for CH 81 3 Br for the intensity fit. Only the leading term of the dipole transition expansion d 6 = µ q 6 is needed to obtain a root-mean-square deviation close to the experimental accuracy of 5%. This intensity parameter is defined by the expression (16) v 6 = 0, l = 0, J, K µ t Z v6 = 1, l ± 1, J, K ± 1 =± 1 2 d 6F ± 11 (m, K ) [5a] v 6 = 0, l = 0, J, K µ t Z v6 = 1, l ± 1, J, K ± 1 =± 1 2 d 6F ± 01 (J, K ), [5b] where µ T Z is the M-reduced transition moment defined in Ref. (16). The F function, also defined in Ref. (16), depends on m and K, the rotational quantum numbers; m = J + 1 J and J for J = J + 1(R branch), J 1(P branch), and J (Q branch) respectively: and [ ] 2J + 1 1/2 F ± 01 (J, K ) = [(J K )(J ± K + 1)] 1/2 J(J + 1) [ ] F ± m (m ± K )(m ± K + 1) 1/2 11 (m, K ) =±. [5c] m m No dependence of the leading term d 6 on J or K is required in our fit, as introduction of these parameters does not decrease the standard deviation. The vibrational transition dipole moment µ ν is directly related to d 6 and was found to be µ v 79 = d 6 = (9)D µ v 81 = d 6 = (9)D. The spectra are taken with bromide in natural abundance, i.e., 50.54% 79 Br and 49.46% 81 Br, so the vibrational band strength Sv 0 is calculated from Sv 0 = 8π 3 3hc T 0 [ ν79 0 T Q 79 V µ v 2 79 ν Q 81 V ] µ v 2 81, where Q v is the vibrational partition function (Q v = ( ) are the values we calculated for CH 79 3 Br and CH 81 3 Br, respectively); and ν0 79 and ν81 0 are the wavenumbers at the ν 6 band center of each isotope given in Table 2. The value derived for Sv 0 at 296 K, is S0 v = 26.60(9) cm 2 atm 1. To evaluate the coherence of the treatment, a comparison between this value and the value of the integrated (total) bandstrength defined as the sum of all individual absolute intensities, I B A = 25(1) cm 2 atm 1, was made at 296 K. The two values are very close. In Table 3, we show the values of the vibrational transition dipole moment; we obtained the vibrational and integrated bandstrengths and then we compared to the values from the low-resolution studies (11 14). In the present work, for the first time, a value for the bandstrength is derived from an analysis of individual line intensities. In all the earlier studies, the TABLE 3 Vibrational Transition Dipole Moment a and Statistics for Fitted Intensities of the ν 6 Band of CH 3 Br CH 3 79 Br [6] [7] CH 3 81 Br µ v (Debye) (9) (9) # lines b % rms 4.9% 4.9% Bandstrengths and integrated strength c Present work Ref. (14) Ref. (13) Ref. (12) Ref. (11) Integrated 27(5) 29.8(2) 29.5(2) 24.6 absorption coefficient Sv (9) I B A 25(1) a The quoted errors represent one standard deviation. b Number of transitions included in fit. c Vibrational bandstrength Sv 0 and integrated (sum of calculated intensities) bandstrength IA B in cm 2 atm 1 at 296 K. The integrated bandstrength are calculated with an estimated 5% precision.

5 34 BRUNETAUD, KLEINER, AND LACOME FIG. 2. J dependence and comparison between measured line intensities ( R P branch; R Q branch; R R branch) and calculated (solid line) for the K = 2 subbranches of CH 79 3 Br. For J = 1, m = J; for J = 0, m = J; for J =+1, m = J + 1. FIG. 3. Comparison between observed (solid line) and synthetic ( ) spectra. Obs-calc is shown at the bottom and is always lower than 4%. The experimental resolution is cm 1, the optical path is 4.15 m, the pressure is Torr, and T = 296 K. values were determined from integrated band absorption in lowresolution spectra. The set of results in Table 3 shows good agreement between our study and Ref. (14). Our measurement is not far from the average of the previous references but values from references (12, 13) are higher than ours, while the value from the oldest study (11) islower. Tables 4 and 5 show a comparison between measured and calculated intensities for both isotopomers of CH 3 Br. For each line, we included the line assignments (lower and upper levels), the observed wavenumbers, the measured intensities (S 0 ), the calculated intensities (S c ), and the difference between measured and calculated intensities in percent (S 0 S c /S 0 ) for CH 3 79 Br and CH 3 81 Br, respectively. Figure 2 illustrates the good agree- ment between measured and calculated line intensities for R P, R Q, and R R subbranches for the lower state K = 2ofCH 3 79 Br. LINE-BY-LINE PREDICTION Using the energy and intensity parameters presented above, we generated a prediction of line positions and intensities with intensities greater than 10 5 cm 2 atm 1 at 296 K for both isotopomers up to J = 60, from 820 to 1120 cm 1, a reasonable limit for atmospheric purposes. This prediction is available at the journal or with I. Kleiner or N. Lacome. To illustrate the quality of our results, Fig. 3 shows the observed and synthetic spectra of methyl bromide from TABLE 4 Comparison Between Measured and Calculated Intensities for CH 3 79 Br CH 3 Br : isotope 79 (P) P (41, E, 4) 40 E nu E E (P) P (20, A+, 6) 19 A nu E E (P) P (9, E, 7) 8 E nu E E (P) P (48, A+, 3) 47 A nu E E (P) P (20, E, 5) 19 E nu E E (P) Q (50, A, 6) 50 A nu E E (P) P (10, E, 5) 9 E nu E E (P) P (20, E, 4) 19 E nu E E (P) P (9, E, 5) 8 E nu E E (I) Lower state quantum numbers. (II) Upper state quantum numbers. (III) Vibrational Band. (IV) Observed frequencies (in cm 1 ). (V) Observed intensities in cm 2 atm 1 at 296. (VI) Calculated intensities in cm 2 atm 1 at 296 K. (VII) (Scalc-Sobs)/Sobs in %.

6 LINE INTENSITIES OF CH 3 Br AT 10 µm 35 TABLE 4 Continued CH 3 Br : isotope 79 (P) P (19, E, 4) 18 E nu E E (P) Q (59, E, 5) 59 E nu E E (P) P (38, E, 2) 37 E nu E E (P) Q (41, E, 5) 41 E nu E E (P) P (14, E, 4) 13 E nu E E (P) Q (39, E, 5) 39 E nu E E (P) Q (37, E, 5) 37 E nu E E (P) Q (36, E, 5) 36 E nu E E (P) R (8, A+, 6) 9 A nu E E (P) Q (34, E, 5) 34 E nu E E (P) P (34, E, 2) 33 E nu E E (P) R (11, A+, 6) 12 A nu E E (P) P (21, A+, 3) 20 A nu E E (P) P (31, E, 2) 30 E nu E E (P) R (12, A+, 6) 13 A nu E E (P) P (41, E, 1) 40 E nu E E (P) P (20, A+, 3) 19 A nu E E (P) P (9, E, 4) 8 E nu E E (P) R (25, E, 7) 26 E nu E E (P) P (30, E, 2) 29 E nu E E (P) P (19, A+, 3) 18 A nu E E (P) P (7, E, 4) 6 E nu E E (P) P (16, A+, 3) 15 A nu E E (P) P (37, E, 1) 36 E nu E E (P) Q (49, E, 4) 49 E nu E E (P) Q (48, E, 4) 48 E nu E E (P) R (18, A+, 6) 19 A nu E E (P) Q (47, E, 4) 47 E nu E E (R) P (46, A+, 0) 45 A nu E E (P) Q (46, E, 4) 46 E nu E E (P) P (36, E, 1) 35 E nu E E (P) Q (45, E, 4) 45 E nu E E (P) Q (41, E, 4) 41 E nu E E (P) Q (40, E, 4) 40 E nu E E (P) P (35, E, 1) 34 E nu E E (P) Q (38, E, 4) 38 E nu E E (P) R (32, E, 7) 33 E nu E E (P) Q (37, E, 4) 37 E nu E E (P) Q (36, E, 4) 36 E nu E E (P) Q (34, E, 4) 34 E nu E E (P) R (11, E, 5) 12 E nu E E (P) R (23, A+, 6) 24 A nu E E (P) P (21, E, 2) 20 E nu E E (P) P (31, E, 1) 30 E nu E E (R) P (41, A+, 0) 40 A nu E E (P) P (19, E, 2) 18 E nu E E (P) Q (55, A, 3) 55 A nu E E (P) R (29, A+, 6) 30 A nu E E (R) P (48, E, 1) 47 E nu E E (P) Q (54, A, 3) 54 A nu E E (P) R (17, E, 5) 18 E nu E E (P) P (5, A+, 3) 4 A nu E E (P) P (16, E, 2) 15 E nu E E

7 36 BRUNETAUD, KLEINER, AND LACOME TABLE 4 Continued CH 3 Br : isotope 79 (R) P (37, A+, 0) 36 A nu E E (P) Q (51, A, 3) 51 A nu E E (P) Q (50, A, 3) 50 A nu E E (R) P (36, A+, 0) 35 A nu E E (P) P (14, E, 2) 13 E nu E E (P) R (32, A+, 6) 33 A nu E E (P) R (20, E, 5) 21 E nu E E (P) P (11, E, 2) 10 E nu E E (P) R (23, E, 5) 24 E nu E E (P) R (11, E, 4) 12 E nu E E (R) P (43, E, 1) 42 E nu E E (P) R (36, A+, 6) 37 A nu E E (P) R (24, E, 5) 25 E nu E E (P) P (21, E, 1) 20 E nu E E (P) P (10, E, 2) 9 E nu E E (P) P (8, E, 2) 7 E nu E E (P) P (19, E, 1) 18 E nu E E (R) P (29, A+, 0) 28 A nu E E (P) R (16, E, 4) 17 E nu E E (R) P (28, A+, 0) 27 A nu E E (R) P (27, A+, 0) 26 A nu E E (P) P (5, E, 2) 4 E nu E E (P) Q (48, E, 2) 48 E nu E E (P) Q (46, E, 2) 46 E nu E E (R) P (47, E, 2) 46 E nu E E (P) P (15, E, 1) 14 E nu E E (P) Q (45, E, 2) 45 E nu E E (P) Q (42, E, 2) 42 E nu E E (R) P (36, E, 1) 35 E nu E E (R) P (25, A+, 0) 24 A nu E E (R) P (46, E, 2) 45 E nu E E (P) R (20, E, 4) 21 E nu E E (P) Q (26, E, 2) 26 E nu E E (R) P (55, A+, 3) 54 A nu E E (P) R (23, E, 4) 24 E nu E E (P) R (24, E, 4) 25 E nu E E (R) P (32, E, 1) 31 E nu E E (R) P (21, A+, 0) 20 A nu E E (P) P (10, E, 1) 9 E nu E E (P) R (13, A+, 3) 14 A nu E E (P) P (8, E, 1) 7 E nu E E (P) P (7, E, 1) 6 E nu E E (P) R (43, E, 5) 44 E nu E E (P) R (57, A+, 6) 58 A nu E E (P) Q (54, E, 1) 54 E nu E E (R) P (38, E, 2) 37 E nu E E (P) Q (53, E, 1) 53 E nu E E (P) P (5, E, 1) 4 E nu E E (P) Q (52, E, 1) 52 E nu E E (P) Q (51, E, 1) 51 E nu E E (P) Q (49, E, 1) 49 E nu E E (P) Q (48, E, 1) 48 E nu E E (P) Q (46, E, 1) 46 E nu E E

8 LINE INTENSITIES OF CH 3 Br AT 10 µm 37 TABLE 4 Continued CH 3 Br : isotope 79 (R) P (26, E, 1) 25 E nu E E (P) Q (44, E, 1) 44 E nu E E (P) R (32, E, 4) 33 E nu E E (R) P (47, A+, 3) 46 A nu E E (P) Q (43, E, 1) 43 E nu E E (P) Q (42, E, 1) 42 E nu E E (P) Q (40, E, 1) 40 E nu E E (R) P (36, E, 2) 35 E nu E E (P) R (8, E, 2) 9 E nu E E (R) P (46, A+, 3) 45 A nu E E (P) R (12, E, 2) 13 E nu E E (R) P (32, E, 2) 31 E nu E E (P) R (13, E, 2) 14 E nu E E (P) R (14, E, 2) 15 E nu E E (R) P (6, A+, 0) 5 A nu E E (R) P (39, A+, 3) 38 A nu E E (P) R (17, E, 2) 18 E nu E E (R) P (28, E, 2) 27 E nu E E (P) R (30, A+, 3) 31 A nu E E (R) P (5, A+, 0) 4 A nu E E (P) R (44, E, 4) 45 E nu E E (P) R (18, E, 2) 19 E nu E E (P) R (6, E, 1) 7 E nu E E (R) P (16, E, 1) 15 E nu E E (P) R (31, A+, 3) 32 A nu E E (R) P (27, E, 2) 26 E nu E E (R) P (15, E, 1) 14 E nu E E (P) R (46, E, 4) 47 E nu E E (R) Q (44, A+, 0) 44 A nu E E (P) R (8, E, 1) 9 E nu E E (R) P (25, E, 2) 24 E nu E E (R) Q (45, A, 3) 45 A nu E E (R) Q (44, A, 3) 44 A nu E E (R) R (15, E, 2) 16 E nu E E (R) Q (50, E, 4) 50 E nu E E (R) R (19, A+, 3) 20 A nu E E (R) R (47, E, 1) 48 E nu E E (R) Q (47, E, 5) 47 E nu E E (R) R (20, A+, 3) 21 A nu E E (R) Q (40, E, 5) 40 E nu E E (R) R (35, E, 2) 36 E nu E E (R) Q (36, E, 5) 36 E nu E E (R) Q (35, E, 5) 35 E nu E E (R) Q (33, E, 5) 33 E nu E E (R) Q (31, E, 5) 31 E nu E E (R) R (36, E, 2) 37 E nu E E (R) Q (30, E, 5) 30 E nu E E (R) R (38, E, 2) 39 E nu E E (R) R (14, E, 4) 15 E nu E E (R) R (18, E, 4) 19 E nu E E (R) Q (47, A, 6) 47 A nu E E (R) Q (45, A, 6) 45 A nu E E (R) R (34, A+, 3) 35 A nu E E

9 38 BRUNETAUD, KLEINER, AND LACOME TABLE 4 Continued CH 3 Br : isotope 79 (R) Q (44, A, 6) 44 A nu E E (R) P (38, A+, 9) 37 A nu E E (R) R (21, E, 4) 22 E nu E E (R) Q (42, A, 6) 42 A nu E E (R) Q (41, A, 6) 41 A nu E E (R) Q (40, A, 6) 40 A nu E E (R) R (35, A+, 3) 36 A nu E E (R) Q (39, A, 6) 39 A nu E E (R) Q (38, A, 6) 38 A nu E E (R) Q (31, A, 6) 31 A nu E E (R) Q (30, A, 6) 30 A nu E E (R) Q (29, A, 6) 29 A nu E E (R) R (12, E, 5) 13 E nu E E (R) R (27, E, 4) 28 E nu E E (R) R (41, A+, 3) 42 A nu E E (R) R (28, E, 4) 29 E nu E E (R) R (15, E, 5) 16 E nu E E (R) R (16, E, 5) 17 E nu E E (R) R (44, A+, 3) 45 A nu E E (R) R (30, E, 4) 31 E nu E E (R) R (17, E, 5) 18 E nu E E (R) R (46, A+, 3) 47 A nu E E (R) Q (49, E, 7) 49 E nu E E (R) R (20, E, 5) 21 E nu E E (R) R (34, E, 4) 35 E nu E E (R) Q (44, E, 7) 44 E nu E E (R) Q (33, E, 7) 33 E nu E E (R) Q (28, E, 7) 28 E nu E E (R) Q (25, E, 7) 25 E nu E E (R) R (25, E, 5) 26 E nu E E (R) R (39, E, 4) 40 E nu E E (R) R (12, A+, 6) 13 A nu E E (R) R (13, A+, 6) 14 A nu E E (R) R (14, A+, 6) 15 A nu E E (R) R (15, A+, 6) 16 A nu E E (R) R (43, E, 4) 44 E nu E E (R) R (29, E, 5) 30 E nu E E (R) R (59, A+, 3) 60 A nu E E (R) R (44, E, 4) 45 E nu E E (R) R (30, E, 5) 31 E nu E E (R) R (45, E, 4) 46 E nu E E (R) R (31, E, 5) 32 E nu E E (R) R (18, A+, 6) 19 A nu E E (R) R (19, A+, 6) 20 A nu E E (R) R (20, A+, 6) 21 A nu E E (R) R (34, E, 5) 35 E nu E E (R) R (49, E, 4) 50 E nu E E (R) Q (45, E, 8) 45 E nu E E (R) R (21, A+, 6) 22 A nu E E (R) R (35, E, 5) 36 E nu E E (R) R (9, E, 7) 10 E nu E E (R) Q (37, E, 8) 37 E nu E E (R) R (36, E, 5) 37 E nu E E

10 LINE INTENSITIES OF CH 3 Br AT 10 µm 39 TABLE 4 Continued CH 3 Br : isotope 79 (R) Q (36, E, 8) 36 E nu E E (R) Q (33, E, 8) 33 E nu E E (R) Q (31, E, 8) 31 E nu E E (R) R (23, A+, 6) 24 A nu E E (R) Q (30, E, 8) 30 E nu E E (R) R (10, E, 7) 11 E nu E E (R) Q (29, E, 8) 29 E nu E E (R) Q (28, E, 8) 28 E nu E E (R) Q (27, E, 8) 27 E nu E E (R) Q (26, E, 8) 26 E nu E E (R) Q (25, E, 8) 25 E nu E E (R) Q (22, E, 8) 22 E nu E E (R) R (24, A+, 6) 25 A nu E E (R) Q (19, E, 8) 19 E nu E E (R) R (11, E, 7) 12 E nu E E (R) Q (18, E, 8) 18 E nu E E (R) R (25, A+, 6) 26 A nu E E (R) R (39, E, 5) 40 E nu E E (R) R (12, E, 7) 13 E nu E E (R) R (55, E, 4) 56 E nu E E (R) R (13, E, 7) 14 E nu E E (R) R (27, A+, 6) 28 A nu E E (R) R (14, E, 7) 15 E nu E E (R) R (42, E, 5) 43 E nu E E (R) R (28, A+, 6) 29 A nu E E (R) R (15, E, 7) 16 E nu E E (R) R (29, A+, 6) 30 A nu E E (R) R (30, A+, 6) 31 A nu E E (R) R (17, E, 7) 18 E nu E E (R) R (45, E, 5) 46 E nu E E (R) R (31, A+, 6) 32 A nu E E (R) R (32, A+, 6) 33 A nu E E (R) Q (58, A, 9) 58 A nu E E (R) R (19, E, 7) 20 E nu E E (R) R (34, A+, 6) 35 A nu E E (R) R (35, A+, 6) 36 A nu E E (R) Q (44, A, 9) 44 A nu E E (R) Q (42, A, 9) 42 A nu E E (R) Q (41, A, 9) 41 A nu E E (R) Q (36, A, 9) 36 A nu E E (R) R (12, E, 8) 13 E nu E E (R) R (55, E, 5) 56 E nu E E (R) R (13, E, 8) 14 E nu E E (R) R (27, E, 7) 28 E nu E E (R) R (14, E, 8) 15 E nu E E (R) R (42, A+, 6) 43 A nu E E (R) R (28, E, 7) 29 E nu E E (R) R (15, E, 8) 16 E nu E E (R) R (43, A+, 6) 44 A nu E E (R) R (29, E, 7) 30 E nu E E (R) R (16, E, 8) 17 E nu E E (R) R (44, A+, 6) 45 A nu E E

11 40 BRUNETAUD, KLEINER, AND LACOME TABLE 4 Continued CH 3 Br : isotope 79 (R) R (30, E, 7) 31 E nu E E (R) R (45, A+, 6) 46 A nu E E (R) R (17, E, 8) 18 E nu E E (R) R (31, E, 7) 32 E nu E E (R) R (46, A+, 6) 47 A nu E E (R) R (18, E, 8) 19 E nu E E (R) R (19, E, 8) 20 E nu E E (R) R (33, E, 7) 34 E nu E E (R) R (48, A+, 6) 49 A nu E E (R) R (20, E, 8) 21 E nu E E (R) R (34, E, 7) 35 E nu E E (R) Q (39, E, 10) 39 E nu E E (R) R (51, A+, 6) 52 A nu E E (R) Q (37, E, 10) 37 E nu E E (R) R (10, A+, 9) 11 A nu E E (R) Q (28, E, 10) 28 E nu E E (R) R (53, A+, 6) 54 A nu E E (R) R (24, E, 8) 25 E nu E E (R) R (11, A+, 9) 12 A nu E E (R) R (12, A+, 9) 13 A nu E E (R) R (40, E, 7) 41 E nu E E (R) R (26, E, 8) 27 E nu E E (R) R (13, A+, 9) 14 A nu E E (R) R (41, E, 7) 42 E nu E E (R) R (27, E, 8) 28 E nu E E (R) R (14, A+, 9) 15 A nu E E (R) R (15, A+, 9) 16 A nu E E (R) R (43, E, 7) 44 E nu E E (R) R (29, E, 8) 30 E nu E E (R) R (44, E, 7) 45 E nu E E (R) R (16, A+, 9) 17 A nu E E (R) R (17, A+, 9) 18 A nu E E (R) R (31, E, 8) 32 E nu E E (R) R (18, A+, 9) 19 A nu E E (R) R (32, E, 8) 33 E nu E E (R) R (19, A+, 9) 20 A nu E E (R) R (33, E, 8) 34 E nu E E (R) R (20, A+, 9) 21 A nu E E (R) R (34, E, 8) 35 E nu E E (R) R (35, E, 8) 36 E nu E E (R) R (22, A+, 9) 23 A nu E E (R) R (23, A+, 9) 24 A nu E E (R) Q (32, E, 11) 32 E nu E E

12 LINE INTENSITIES OF CH 3 Br AT 10 µm 41 TABLE 5 Comparison Between Measured and Calculated Intensities for CH 3 81 Br CH 3 Br : isotope 81 (P) P (41, E, 4) 40 E nu E E (P) P (40, E, 4) 39 E nu E E (P) P (21, E, 5) 20 E nu E E (P) P (20, E, 5) 19 E nu E E (P) Q (49, A, 6) 49 A nu E E (P) P (21, E, 4) 20 E nu E E (P) P (20, E, 4) 19 E nu E E (P) P (19, E, 4) 18 E nu E E (P) P (17, E, 4) 16 E nu E E (P) Q (48, E, 5) 48 E nu E E (P) P (15, E, 4) 14 E nu E E (P) Q (47, E, 5) 47 E nu E E (P) P (36, E, 2) 35 E nu E E (P) Q (45, E, 5) 45 E nu E E (P) P (46, E, 1) 45 E nu E E (P) Q (41, E, 5) 41 E nu E E (P) R (19, E, 7) 20 E nu E E (P) P (14, E, 4) 13 E nu E E (P) Q (38, E, 5) 38 E nu E E (P) Q (36, E, 5) 36 E nu E E (P) P (13, E, 4) 12 E nu E E (P) P (34, E, 2) 33 E nu E E (P) Q (29, E, 5) 29 E nu E E (P) P (32, E, 2) 31 E nu E E (P) R (11, A+, 6) 12 A nu E E (P) R (12, A+, 6) 13 A nu E E (P) R (24, E, 7) 25 E nu E E (P) P (31, E, 2) 30 E nu E E (P) P (41, E, 1) 40 E nu E E (P) P (20, A+, 3) 19 A nu E E (P) P (30, E, 2) 29 E nu E E (P) P (19, A+, 3) 18 A nu E E (P) R (15, A+, 6) 16 A nu E E (P) R (17, A+, 6) 18 A nu E E (P) P (5, E, 4) 4 E nu E E (P) P (37, E, 1) 36 E nu E E (P) Q (51, E, 4) 51 E nu E E (R) P (46, A+, 0) 45 A nu E E (P) Q (45, E, 4) 45 E nu E E (P) P (36, E, 1) 35 E nu E E (P) Q (41, E, 4) 41 E nu E E (P) Q (40, E, 4) 40 E nu E E (P) Q (39, E, 4) 39 E nu E E (P) R (8, E, 5) 9 E nu E E (P) Q (36, E, 4) 36 E nu E E (P) Q (35, E, 4) 35 E nu E E (P) Q (34, E, 4) 34 E nu E E (P) R (23, A+, 6) 24 A nu E E (I) Lower state quantum numbers. (II) Upper state quantum numbers. (III) Vibrational Band. (IV) Observed frequencies (in cm 1 ). (V) Observed intensities in cm 2 atm 1 at 296. (VI) Calculated intensities in cm 2 atm 1 at 296 K. (VII) (Scalc-Sobs)/Sobs in %.

13 42 BRUNETAUD, KLEINER, AND LACOME TABLE 5 Continued CH 3 Br : isotope 81 (P) P (32, E, 1) 31 E nu E E (P) P (21, E, 2) 20 E nu E E (P) P (10, A+, 3) 9 A nu E E (P) P (31, E, 1) 30 E nu E E (P) R (25, A+, 6) 26 A nu E E (P) P (20, E, 2) 19 E nu E E (P) R (14, E, 5) 15 E nu E E (P) P (8, A+, 3) 7 A nu E E (P) P (19, E, 2) 18 E nu E E (P) Q (60, A, 3) 60 A nu E E (P) R (28, A+, 6) 29 A nu E E (P) Q (55, A, 3) 55 A nu E E (P) Q (54, A, 3) 54 A nu E E (P) P (5, A+, 3) 4 A nu E E (P) P (16, E, 2) 15 E nu E E (R) P (37, A+, 0) 36 A nu E E (P) Q (50, A, 3) 50 A nu E E (P) R (18, E, 5) 19 E nu E E (P) Q (49, A, 3) 49 A nu E E (P) Q (45, A, 3) 45 A nu E E (P) Q (44, A, 3) 44 A nu E E (P) R (19, E, 5) 20 E nu E E (P) P (3, A+, 3) 2 A nu E E (P) P (14, E, 2) 13 E nu E E (P) Q (34, A, 3) 34 A nu E E (P) Q (34, A+, 3) 34 A nu E E (P) P (23, E, 1) 22 E nu E E (R) P (43, E, 1) 42 E nu E E (R) P (32, A+, 0) 31 A nu E E (P) R (12, E, 4) 13 E nu E E (P) P (21, E, 1) 20 E nu E E (P) P (8, E, 2) 7 E nu E E (P) P (19, E, 1) 18 E nu E E (P) P (6, E, 2) 5 E nu E E (P) R (43, A+, 6) 44 A nu E E (P) P (5, E, 2) 4 E nu E E (P) Q (52, E, 2) 52 E nu E E (R) P (37, E, 1) 36 E nu E E (P) Q (46, E, 2) 46 E nu E E (P) Q (45, E, 2) 45 E nu E E (P) R (19, E, 4) 20 E nu E E (P) R (7, A+, 3) 8 A nu E E (R) P (47, E, 2) 46 E nu E E (P) R (32, E, 5) 33 E nu E E (P) Q (42, E, 2) 42 E nu E E (R) P (36, E, 1) 35 E nu E E (P) P (3, E, 2) 2 E nu E E (P) Q (40, E, 2) 40 E nu E E (P) Q (37, E, 2) 37 E nu E E (P) R (11, A+, 3) 12 A nu E E (R) P (43, E, 2) 42 E nu E E (P) R (12, A+, 3) 13 A nu E E (P) R (51, A+, 6) 52 A nu E E (P) P (10, E, 1) 9 E nu E E (R) P (42, E, 2) 41 E nu E E (R) P (30, E, 1) 29 E nu E E

14 LINE INTENSITIES OF CH 3 Br AT 10 µm 43 TABLE 5 Continued CH 3 Br : isotope 81 (R) P (19, A+, 0) 18 A nu E E (P) P (7, E, 1) 6 E nu E E (P) R (30, E, 4) 31 E nu E E (P) P (5, E, 1) 4 E nu E E (R) P (38, E, 2) 37 E nu E E (P) Q (52, E, 1) 52 E nu E E (R) P (16, A+, 0) 15 A nu E E (P) Q (48, E, 1) 48 E nu E E (R) P (15, A+, 0) 14 A nu E E (P) Q (44, E, 1) 44 E nu E E (P) Q (43, E, 1) 43 E nu E E (R) P (47, A+, 3) 46 A nu E E (P) Q (42, E, 1) 42 E nu E E (P) P (3, E, 1) 2 E nu E E (P) R (20, A+, 3) 21 A nu E E (P) Q (40, E, 1) 40 E nu E E (P) Q (39, E, 1) 39 E nu E E (R) P (36, E, 2) 35 E nu E E (P) R (33, E, 4) 34 E nu E E (R) P (14, A+, 0) 13 A nu E E (P) Q (38, E, 1) 38 E nu E E (R) P (46, A+, 3) 45 A nu E E (P) R (21, A+, 3) 22 A nu E E (P) R (34, E, 4) 35 E nu E E (P) R (9, E, 2) 10 E nu E E (R) P (43, A+, 3) 42 A nu E E (R) P (10, A+, 0) 9 A nu E E (P) R (25, A+, 3) 26 A nu E E (P) R (13, E, 2) 14 E nu E E (P) R (17, E, 2) 18 E nu E E (R) P (39, A+, 3) 38 A nu E E (R) P (17, E, 1) 16 E nu E E (R) P (28, E, 2) 27 E nu E E (R) P (5, A+, 0) 4 A nu E E (P) R (18, E, 2) 19 E nu E E (P) R (6, E, 1) 7 E nu E E (R) P (16, E, 1) 15 E nu E E (R) P (27, E, 2) 26 E nu E E (P) R (19, E, 2) 20 E nu E E (R) P (37, A+, 3) 36 A nu E E (P) R (20, E, 2) 21 E nu E E (P) R (33, A+, 3) 34 A nu E E (R) P (3, A+, 0) 2 A nu E E (R) P (25, E, 2) 24 E nu E E (P) R (9, E, 1) 10 E nu E E (R) R (20, E, 1) 21 E nu E E (R) Q (43, A, 3) 43 A nu E E (R) R (12, E, 2) 13 E nu E E (R) R (14, E, 2) 15 E nu E E (R) R (27, E, 1) 28 E nu E E (R) Q (50, E, 4) 50 E nu E E (R) Q (44, E, 4) 44 E nu E E (R) Q (43, E, 4) 43 E nu E E (R) Q (40, E, 4) 40 E nu E E (R) R (28, E, 2) 29 E nu E E (R) R (30, E, 2) 31 E nu E E