Infrared, Far Infrared and Millimeter Wave Spectroscopy of Methanol-D 1 : New and Revised Assignments for Torsional-Rotational Transitions

Transcription

1 Infrared, Far Infrared and Millimeter Wave Spectroscopy of Methanol-D 1 : New and Revised Assignments for Torsional-Rotational Transitions Indra Mukhopadhyay Physics and Engineering Department Darton State College, Albany, GA 31707, USA indra.mukhopadhyay@darton.edu Abstract: In this paper, new spectral measurements and analyses are reported in the millimeter wave (MMW), far infrared (FIR) and infrared (IR) regions of the electromagnetic spectrum for methanol-d 1 molecular species. Revised and corrected assignments are presented for many transitions recently reported by others, which now need a revised analysis. Although molecular medium (CH 2DOH) in the current study exhibits a complex spectra assignments were possible for a large number of transitions. Since there is a scarcity of frequency standard in the MMW and FIR regions a catalog of all the assigned and measured transitions frequencies can be obtained from the author via . To demonstrate the quality of the spectra, some of the bands recorded are shown. The experimental details of the Sub Millimeter and Infrared techniques are provided. Keywords: MMW, FTIR, FIR, Spectroscopy, Methanol, Astrophysics. I. INTRODUCTION The MMW and FIR spectral region is by far the least explored portion of the electromagnetic spectrum, largely because of the difficulty of generating and detecting radiation at these wavelengths. However, over the years, a number of approaches have been developed. These include nonlinear harmonic generation, tunable microwave sideband optically pumped far infrared (FIR) lasers, fundamental solid state oscillator sources and vacuum tube based systems. In this work a backward wave tube based fast scan system at the Ohio State University has been used. This system has broad tenability, reasonable power outputs, good spectral purity and the wade frequency of operation in the MMW region. Further applications of MMW and FIR techniques and relevant molecular studies can be found in Refs. [1-20]. As far as the FIR region is concerned, the Fourier Transform technique has been widely used and commercial systems such as Bruker systems are well known. The description of the system can be found in many places. A Fourier Transform (FT) spectrometer is essentially a modified Michelson interferometer, where intensity modulations are generated to uncover the spectral composition of the radiation under study. Thereby, two beams are derived from the incoming beam by amplitude division at the beam-splitter and a path difference is introduced before the recombination of the beams. The resulting intensity in the recombined beam is given by the path difference and the spectral composition to be derived. In the measurement process, the path difference is varied and the associated intensity fluctuations are recorded. The intensity fluctuations are assigned to the optical path difference by means of a laser. The limitations of this method are mainly the weak signal obtained in this region conventional source. However spectra in the region cm -1 spectrum are routinely recorded by commercial FTIR spectrometer with a high resolution of the order of cm -1. In this work the Bruker IFS-120 system at the Justus Liebig Universität in Giessen, Germany, has been used. It is proposed to record the spectra using a synchrotron radiation source at the Canadian Light Source with much better signal/noise ratio at a resolution on the order of cm -1 [21]. II. EXPERIMENTAL ASPECTS The details of the fast scan MMW system can be found in the paper by Prof. F.C. DeLucia [12] at the Ohio State University. The spectra were recorded in a number of closely spaced ranges: , , , , , and GHz for CH2DOH and , , , , , and GHz for CHD2OH. The selection of these ranges seems random but it was decided by the BWO equipped with the spectrometer at the time when the instrument was available for the present measurements. The spectra were recorded at approximate pressure of.1 millitorr. Available 195

2 In the FIR and IR the high resolution FTIR spectrum has been recorded using the Bruker IFS 120 high resolution spectrometer at the Winnewisser laboratory of the Justus Liebig Universität in Germany. The CH2DOH sample used was supplied by Cambridge Isotope Laboratories, and was 98 % pure. The sample was used without any further purification. A sample pressure of about 2.4 mbar was used at a temperature of 24 Celsius in a multi-pass cell of base length 1 m and was adjusted to get an absorption path length of 3.28 m. The spectrum was recorded in the range cm-1 with a nominal resolution of cm -1. The IR spectrum was extended up to 1200 cm -1, to include the CO-stretch band. Thus for CH 2DOH the coverage was for the complete torsional band extending up to about 800 cm-1 and then OCD bending band (892 cm-1) and the C-O stretch bands with Q-heads at 1021 cm -1 and 1059 cm -1 (see for Figs 1-7). For CHD 2OH Fig 1. Spectra around 860 cm -1 showing complex structure. For all the IR & FIR spectra the wave numbers in cm -1 are presented along the X-axis and the Relative Intensity in arbitrary units along the Y-axis. Fig. 2. A representative portion of the spectra showing the strong starting of a P P branch and a well resolved Q-branch. the complete coverage was obtained from cm-1. This includes the torsional bands: ν 11 (CD2 Twisting), ν 8 and ν 10 (CD 2 Wagging); ν 7 and ν 9 (CO Stretch) and ν 8 (CD 2 bending) bands. These bands show extremely complicated structure and their study corroborates the ground state study and will be the subject matter of future communications. These studies along with vibrational relaxation studies would throw some light in the illusive vibrational rotational energy pathways and allow discovery of new sources for FIR laser lines. The FIR spectrum was also run at -60 o C at a relatively low pressure of 0.15 millitorr to simplify the assignment process. III. BACKGROUND INFORMATION The torsional rotational vibrational interactions and the experimental difficulty in searching through large spectral regions with poorly predicted transition frequencies complicate the spectroscopy of asymmetrically substituted deuterated methanol (CH2DOH). Analyzing the spectrum of this isotopomer has been one of the severe challenges in molecular spectroscopy. The theory of the asymmetrically deuterated slightly asymmetric internal rotor molecules has been largely developed for last the last three decades by C.R. Quade and coworkers at the Texas tech university [22-27]. The theory has been tested over time with microwave (MW), millimeter wave (MMW), far-infrared (FIR) and IR (regions) with significant success. Later around 1998 [28] the code for the Hamiltonian has been extended to calculate the complete energy level structure up to the so called fifth excited torsional state in normal methanol (here we call it v=15). The matrix elements between all possible transitions were calculated [27] and have been very useful for further assignments of torsional-rotational transitions. Available 196

3 Fig. 3. A Q-branch which turns around and is reassigned inthis work. (See text for details) Fig. 4. A portion of the spectra showing clean and abrupt start of an R branch corresponding to K=4o4 3e1. Asymmetry splitting is observed at higher J. Recently, the ground torsional state MMW transitions and some of the same FIR data with a Hamiltonian has been reported [29]. In the model, a huge number of empirical parameters were used and the data were fitted to within experimental accuracy. However many of the higher order parameters have limited physical significance. In another paper by Hilali et al. [30] reported the analysis of some FIR spectral lines. The assignments were mainly based on various groups of somewhat randomly selected Q-branches with uncertain assignment of rotational angular momentum. The problem stems from the lack of R/P branches in the assignment scheme. Hence many of the Q-branch origins had significant uncertainty because the extrapolation was based of uncertain J- assignments rendering a low resolution analysis from a high resolution spectrum. Some of the assignments also have different torsional quantum number assignments than the actual. Here we provide important revisions of assignments suggested by Hilali et al. [30]. The theoretical details can be found in Ref [27]. Fig. 5. MMW spectra showing clean asymmetry splitting for three consecutive P- branch lines for 6e0 5e0. The Frequency (GHz)along the X-axis is in MHz and the Relative Intensity along the Y-axis is in arbitrary units. Fig. 6. Spectra of the IR bands for the OCD bend and C-O stretch One of the aims of the present work is to present revised assignments where the presence of the P/Q branch lines are used to arrive at the correct assignment Most of our assignment is re-confirmed by the use of combination loops. We also introduce a simplified nomenclature appropriate for traditional methanol spectroscopy. Also in this paper we present the effect of asymmetry in more detail in addition to the modification of potential barriers. Most importantly a catalog of about 5700 measured FIR absorption lines with assignments in the region of Available 197

4 cm-1 is submitted as a depository and can be obtained via from the author. These lines have an estimated accuracy of ±15 MHz and to our knowledge this is the first time such an elaborate catalog of this molecule is being reported in the literature. We propose to present the complete catalog of about 25,000 spectral lines with detailed analyses of at least 6 different high resolution vibrational bands and the ground state torsional-rotational bands of this species and the doubly deuterated species CHD2OH in a series of papers. All the assignments presented in the present work have been confirmed by closed combination loops, which is essentially independent of the model of the Hamiltonian used. It shows that assigning Q-branches solely from the agreement with energy levels should be done with caution. IV. RESULTS AND ANALYSIS The IR spectra showed very complicated structure wherever there were spectral lines but the region below about 800 cm -1 (below which no vibrational fundamentals exist) looked relatively calm. However there remained a few regions where clear and regular spectroscopic structures have been observed. As shown in Fig. 1, in any given region the spectrum looked rather complex but a closer look revealed the identification of a number of R- and Q- sub-bands. The energy levels and transition matrix elements calculated earlier provided important support in the assignment process. As can be seen from Fig 2, the R-branch series (J K=K+1 K+1 K K) starts abruptly with the highest intensity whereas for J K= = K-1 K-1 K K), the abrupt start of the P-branch as shown is Fig. 3 helped the assignment process. The associated Q-branch transitions could then be identified knowing the first member of the R/P branch (The Q-branch would be would be away by 2B eff(k±1) from the first member R/P branch line). Fig 7. OCD Bend and C-O state Spectra of CH2DOH. rather tricky for highly excited torsional states. When the ordering of the K=0,1,2,3 are regular and no other nearby low K levels of the same or other torsional species, then the splitting order is as seen in normal parent species: K=0 is always assigned + symmetry, even K have + levels above the level and for odd K it is just opposite. But when the successive K values do not have regular energy values, K=±2 interaction in the molecule may alter the +/- ordering as was seen for the first excited torsional state of parent methanol species. Therefore assignments of K=0 1 or 1 0 transitional sub-bands may need to be reversed because of the selection rule ± ± for R/P branches and for Q-branches depends on the torsional quanta involved. The above rule applies for even change in the torsional quantum number and should be reversed for odd change in the torsional quantum number. It should also be noted that both P- and R- branches are equally strong for K=0 1 or 1 0. Therefore just assignment of the Q-branch with proper + or would pose uncertainty unless the P- or R- branches are assigned and a proper +/ rule is established for the given sub-band. We use here same the notations used in usual methanol work. Since the molecule is very nearly a prolate top the use of prolate top K p as our K values made the process simplified. The asymmetry splits the lower K levels into + and - levels mainly due to the K=±2 matrix elements. The +/- ordering is In this paper we only present in Table 1, the new or revised assignments [30] in order to conserve journal pages and the complete catalogue of 5700 transitions in the MW, MMW FIR and IR regions can be obtained from the author (indra.mukhopadhyay@darton.edu). The revised assignments yield quite different Q-branch origins Available 198

5 from those used in Ref. [30]. With these results a new analysis of the torsional barrier potential constants V1, V2, and V3 is in progress, the preliminary results yield V1= 8.94 cm-1, V2=2.41 cm -1, and V3= cm -1. To demonstrate the resolution and S/N ratio of the MMW spectrum, few lines with clear asymmetry splitting in the ground state are shown in Fig. 6. Detailed discussion of selected revised sub-bands is presented in the following section. The Q-branch assignments are confirmed by the identification of the corresponding R and/or P branches. In Table-1 only the starting members of the R/P branch members are provided. Some assignments which are legitimate in Ref. [30] are given support by the R/P branch assignments. K = 4, vt =6 K =5, vt =5 which in our notation it is 4 e3 5 o3 The first member of the associated Q-Branch is reported as cm -1 in Ref [47]. However our calculation of energy levels indicate that this Q-branch albeit incorrect J assignment is around 131 cm -1, meaning Kσ=4e3 energy is actually be 5o3 stack hence we expect r Q branch to be visible from intensity calculations. Hence a revised assignment as p Q = 4 e3 5 o3 which is calculated to be at 125 cm-1 with excellent agreement with the observed starting point of Q branch around cm-1. The P and/ or R branch J-assignments also need some adjustments. Here the complete P, Q and R branch assignments are consistent with combination relations confirming the revised reassignment. K = 8, vt = 6 K = 9, vt = 4 in our notation 8 e3 9 e2 This Q branch clearly turns around. This occurs when the upper state effective B value becomes either smaller or larger than the lower state B value in the middle of the branch. In CH2DOH it is quite common to have a widely different distortion constant D which could be even negative in for some states. This Q-branch as used in ref. [30] clearly needs revision. K = 2,7 e3 K = 3, 5 e2 which in our nomenclature 2e3 2e2 The Q-branch assignment is clearly in trouble as can be seen clearly with the support of the first few members of the P-branch lines: P(3) = ,P(4)= ,P(5)= , and P(6)= ; which results the first few members of the q-branch as Q(3)= , Q(4)= , Q(5)= , and Q(6)= , these members were not even considered in the extrapolation Hilali et al. [30]. Since there are large number of such corrections to be made, in Table-1 the name of the branches that need revision and the transitions for new branches that are found in this work are mentioned with few initial lines. As can be seen from Table 1, the J-values of the following Q branches are clearly assigned erroneously by Hilali et al. [30]. Kσ = 3e 3 4o 3 sub band is reported here for the first time. Kσ = 0e 6 1e 2 may have an asymmetry inversion and hence the members chosen with the known selection rules may needs to be reversed, which is a well-known phenomenon in symmetric methanol species cases in methanol [1]. Kσ = 3o 3 2o 1 sub band is a new assignment and shows complicated asymmetry splitting. Here we like to indicate that often the asymmetry splitting may appear to be a nuisance but often can help confirming the assignments, which is the case here. The sub band 0o 3 1e 2 is also a new assignment and we present few members of the q-branch lines so as the sub-band 9o 3 8o 2 which is a new assignment. The assignment for the sub band 7e 3 8e 2 is supported by the identification of P- branch lines which are exceptionally strong. The other information presented in Table 1 should be self-explanatory and could be valuable for further analysis. Some of the branches need special mention: Available 199

6 Table 1 New P- and Q- and R- branch assignments and the Q-branches that needs revisions in CH 2DOH (as reported by Hilali et al. [30] Available 200

7 Table 1 (cont.) Available 201

8 Table 1 (cont.) Available 202

9 Table 1 (cont.) Available 203

10 Kσ = 4o 5 5e 4: This branch from very excited state therefore the Boltzmann factor is supposed to be small but a large matrix element of the dipole moment between these two states is from our paper in Ref. [27] is exceptionally large. Since the Intensity of a transition is proportional to the square of the matrix element. These transitions are very strong. The Q-branch for this transition is shown in Fig. 6. Also shown in Fig. 6, another Q-branch depicting the usual problem encountered in assigning only the Q-branch without the knowledge of R and P branches. This is because the Q-branch look can be deceiving. When the Q-branch starts out very strong and few lines may be blended together at the starting J quantum numbers. V. COMMENTS ON FERMI AND CORIOLIS INTERACTIONS Highly excited torsional states may have energies close to that of low lying pure vibrational states and can cause perturbation on the spectra. It is known that OCD- bending mode is around 890 cm -1 can interact with torsional states like e5, o5 etc. through Fermi interaction [20,32-33]. The bending mode flexes the molecule in such way that it enhances the contribution of V1 and V2 terms [28]. Therefore a lot of mixing takes place between the highly excited states and the pure vibrational states consequently causing intensity borrowing effects and some unexpected transitions may become observable. We have succeeded to find some a-type transitions between the lower lying torsional states and the highly excited torsional states of the ground state. From the intensity distribution of a-type Q-branch transitions could be identified and are included in Table 1, at this stage the observations should be treated with care because definite quantum number assignment could not be reached (It should be noted that these a-type transitions are normally forbidden). The Fermi interaction could make a-type transitions between lower lying torsional states to higher lying torsional states visible through intensity borrowing elects from the nearby vibrational state. It is also observed that transitions between e0 in the ground state to e0 state in the OCD fundamental state is strong, whereas the transitions to e1 and o1 states of the bending state practically non-existent. This is supported by an overlap matrix element calculation between the ground state and the OCD bend state [28]. It was observed that Strong Coriolis type interactions (32) are also expected for some closely spaced states. Some of these heavily perturbed transitions have been identified and will be the subject matter for a future communication. VI. CONCLUSIONS In conclusion, new MMW, FIR and IR bands have been analyzed to study the various aspects of the molecular energy levels of asymmetrically deuterated methanol (CH 2DOH). Assignments are reported for the MMW and far infrared (FIR) transitions involving torsionally excited states. Revised assignments are presented for some earlier presented assignments proposed in Ref [30]. The quantum number assignments are also presented for four different pump and FIR laser emission lines. Few laser lines are also predicted. This would allow finding new light sources in the FIR region of the electromagnetic spectrum where there is a scarcity of coherent light sources. A significant Fermi type interaction is observed between the highly excited torsional states of the ground vibrational state and lower lying vibrational states such as the OCD bending and the C-O stretch states, whereas Coriolis interaction is observed between some highly excited torsional states. A number of forbidden transitions which become allowed by intensity borrowing effect have been observed. Finally, a catalog of about 5700 FIR absorption line assignments in the region of cm -1 is prepared and can be had from the author as explained earlier. To our knowledge this is the first time such an elaborate catalog is being reported for Methanol-D 1. ACKNOWLEDGMENT The author is grateful to Profs. Frank DeLucia, Manfred Winnewisser, and Brenda Winnewisser for the use of the experimental facilities. Available 204

11 REFERENCES [1] G. Moruzzi, B.P. Winnewisser, M. Winnewisser, I. Mukhopadhyay and F. Strumia, Microwave, Infrared and Laser Transitions of Methanol: Atlas of Assigned lines from 0 to 1258 cm-1, CRC Press, FL, USA. (1995). ISBN [2] B. Parise, C. Ceccarelli, A.G.G.M. Tielens, E. Herbst, B. Lefloch, E. Caus, A. Castets, I. Mukhopadhyay, L. Pagani and L. Loinard, Detection of Doubly-Deuterated Methanol in the Solar-Type Protostar IRAS , Astronomy & Astrophysics, Vol. 393, L49-L53 (2002). [3] B. Parise, A. Castets, E. Herbst, C. Ceccarelli, I. Mukhopadhyay and A.G.G.M. Tielens, First Detection of Triply-Deuterated Methanol, Astronomy and Astrophysics, A&A 416, (2004). [4] Spectroscopy from Space, Proceedings of the NATO Advanced Research Workshop, held in Bratislava, Slovakia, October 31-November 4, (2000) Ed. by Jean Demaison, Kamil Sarka, and Edward A. Cohen, NATO SCIENCE SERIES: II: Mathematics, Physics and Chemistry, June (2001) SBN &. ISBN [5] B Parise, C. Ceccarelli, A. Tielens, E. Herbst, B. Lefloch, E. Caus, A. Castets, Indra Mukhopadhyay, L. Pagani, and L. Lionard, Detection of Deuterated Methanol in the Low mass Protostar IRAS , In Chemistry as a Disgnostic of Star formation. Proc. Waterloo, Canada (2002), ISBN: [6] B. Parise, C. Ceccarelli, A.G.G.M. Tielens, E. Herbst, B. Lefloch, E. Caus, A. Castets, Indra Mukhopadhyay, L. Pagani and L. Loinard, Detection of Doubly-Deuterated Methanol in the Solar-Type Protostar IRAS , Astronomy & Astrophysics, Vol. 393, L49-L53 (2002). [7] B. Parise, A. Castets, E. Herbst, C. Ceccarelli, Indra Mukhopadhyay and A.G.G.M. Tielens, First Detection of Triply-Deuterated Methanol, Astronomy and Astrophysics, A&A 416, (2004). [8] Spectroscopy from Space, Proceedings of the NATO Advanced Research Workshop, held in Bratislava, Slovakia, October 31-November 4, (2000) Ed. by Jean Demaison, Kamil Sarka, and Edward A. Cohen, NATO SCIENCE SERIES: II: Mathematics, Physics and Chemistry, June (2001) SBN &. ISBN [9] B Parise, C. Ceccarelli, A. Tielens, E. Herbst, B. Lefloch, E. Caus, A. Castets, Indra Mukhopadhyay, L. Pagani, and L. Lionard, Detection of Deuterated Methanol in the Low mass Protostar IRAS , In Chemistry as a Disgnostic of Star formation. Proc. Waterloo, Canada (2002), ISBN: [10] Deuterated methanol in the pre-stellar core L1544, L. Bizzocchi P. Caselli, S. Spezzano and E. Leonardo, Astronomy & Astrophysics, August 12, 2014 [11] E.C.C. Vasconcellos, and K. M. Evenson Far infrared lasing frequencies of CH2DOH, International Journal of Infrared and Millimeter Waves, 11, No. 7, 1990 [12] F.C. DeLucia, Journal of Molecular Spectroscopy 261, 1 17 (2010) [13] G. Ziegler and U. Durr, Submillimeter Laser Action of cw Optically Pumped CD2Cl2, CH2DOH, and CHD20H, IEEE J. Quantum Electron., QE-14, 708 (1978). [14] A.Scalabrin, F.R. Petersen, K.M. Evenson and D.A. Jennings, Optically Pumped cw CH2DOH FIR Laser: and Frequency Measurements, Int. J. of IR and MM Waves, Vol. 1, (1980). [15] D.J.E. Knight, Ordered List of Far Infrared Laser Lines, National Physical Laboratory, Report QU 45, Teddington, U.K. (1982). [16] N.G.Douglas, Millimetre and Submillimetre Wavelength Lasers, Springer Series in Optical Sciences, Vol. 61 (1989) ISBN , Springer Verlag. [17] K.M. Evenson, New short-wavelength laser emissions from partially deuterated methanol isotopes, Appl. Phys. B 74, (2002) [18] De Michele, K. Bousbahi, G. Carelli, and A. Moretti, New FIR Laser Lines from CHD2OH Methanol, International Journal of Infrared and Millimeter Waves, Vol. 24, 233 (2003). [19] Mark McKnight, Patrick Penoyar, Matthew Pruett, Nathan Palmquist, Sumaya Ifland, and Michael Jackson New Far-Infrared Laser Emissions from Optically Pumped CH2DOH, CHD 2OH, and CH 3 18 OH IEEE J Quantum Electron. 50, (2014). Available 205

12 [20] Indra Mukhopadhyay, High Resolution Spectroscopy and Identification of Optically Pumped Far Infrared Laser Lines of Methanol-D 1, Optics Communications, 110, (1994). [21] Brant Billinghurst, Private Communications (2015). [22] C.R. Quade and R.D. Suenram, J. Chem. Phys. 73, 127 (1980). [23] C.F. Su and C.R. Quade, J. Mol. Spectrosc, 134, 290 (1989) [24] C.F. Su and C.R. Quade, J. Chem. Phys. 90 (1989) [25] M. Liu and C.R. Quade, J. Mol. Spectrosc. 146 (1991) [26] C.R. Quade, M. Liu, H. Test, Indra Mukhopadhyay, and N. Suenram, a-dipole Transitions of CH 2DOH in Excited Torsional States, J. Molecular Spectroscopy, Vol. 192, (1998). [27] Indra Mukhopadhyay, Torsional Energies, Matrix Elements and Relative Intensities of Far-Infrared Absorption Transitions in CH 2DOH, Spectrochimica Acta A, U.K., Vol. 53, pp (1997). [28] C.R. Quade, private communication (2004). [29] J C. Pearson, et al., J Mol. Spectrosc. 280, (2012). [30] El Hilali A, et al. J Chem Phys.;135 p.19 (2011). [31] Walter Gordy, Robert Cook, Microwave Molecular Spectra, pp , John Willy, (1970) Library of Congress Catalogue no , SBN [32] Indra Mukhopadhyay, Second Order Coriolis Resonance between the C-O Stretch and the CH 3 Rock Levels of Methanol Involving Excited Torsional States, Spectrochimica Acta A, U.K., Vol. 53, pp (1997). [33] Indra Mukhopadhyay, Forbidden Transitions involving Highly Excited Torsional States in Methanol-D 1 and Confirmation of Optically Pumped Far-Infrared Laser Lines, Spectrocmemica Acta A, Vol. 54, (1998). Personal Profile of Dr. Indra Mukhopadhyay Dr. Indra Mukhopadhyay received the M.Tech. degree in Electronics and Electrical Communication Engineering from the IIT, Kharagpur and received his Ph.D. degree in Physics at the University of New Brunswick. In 1990, He was a Senior Scientist at the Atomic Energy Department. He was involved in various projects including optically pumped molecular lasers, atomic and molecular physics and solid state electronics. In recent years his research interests included Stark Effect, high resolution MMW, FIR and IR Spectroscopy and Radio Astronomy. Dr. Mukhopadhyay was involved with the detection of methanol in a distant Star forming region and the calculation of D/H ratio which has important significance to the "Big Bang" theory. He spent time in various laboratories in USA, Germany, and Canada and is a member of the Canadian Association of Physicists, Indian Laser Association and Laser and Spectroscopy Society of India. He is a member Physics and Astronomy Advisory Committee of the University System of Georgia. Presently he is the Professor of Engineering and Physics at Darton State College, University System of Georgia, USA. He has been nominated for the US professor of the year and for the Excellence in Teaching award by the Georgia Board of regents. Dr. Mukhopadhyay has published more than 100 papers in referred journals. Available 206