Vacuum-Ultraviolet-Excited and CH 2 Cl 2 /H 2 O-Amplified Ionization- Coupled Mass Spectrometry for Oxygenated Organics Analysis

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1 Supporting Information for Vacuum-Ultraviolet-Excited and CH 2 Cl 2 /H 2 O-Amplified Ionization- Coupled Mass Spectrometry for Oxygenated Organics Analysis Bo Yang,, Haixu Zhang,, Jinian Shu*,, Pengkun Ma,, Peng Zhang,, Jingyun Huang,, Zhen Li, and Ce Xu Contents 1. Calibration of the gaseous H 2 O in N 2 with H 18 2 O... S2 2. Mass spectra of acetone and methanol with CH 2 Cl 2 doping under Xe-lamp illumination... S2 3. Determination of the proton source... S3 4. Enhancing effects of four chlorohydrocarbons on ion currents... S6 5. CH 2 Cl 2 -dependent increase of protonated acetone and methanol... S8 6. Observations of the by-product CH 2 O... S9 7. Energy calculations... S10 8. Effects of gaseous H 2 O on the ion formation... S13 9. Chemicals... S References... S16 S1

2 Calibration of the gaseous H 2 O in N 2 with H 18 2 O The gaseous H 2 O in N 2 was calibrated by doping a known amount of H 18 2 O into the balance cylinder. In the experiment, H 18 2 O is injected in the balance cylinder 10 µl by 10 µl until the intensity of the mass peak of (H 18 2 O)H + (m/z = 21) reaches the same signal intensity with that of (H 2 O)H + (m/z = 19). During this process, the wall of the balance cylinder is heated to ~350 K. Assuming that a part of H 18 2 O would be adsorbed by the surface of the mixing and sampling system, the maximum partial flow rate of H 2 O in the ion source is estimated to be molecules s Supporting Figure S1. Time-of-flight mass spectrum of cations generated from residual H 2 O in N 2 and injected H 18 2 O ( molecules s -1 ) doped with CH 2 Cl 2 ( molecules s -1 ) under illumination of a Kr lamp. Mass peaks of m/z 47 and 29 are resulted from the protonated molecular and daughter ions of ethanol which is an impurity desorbed from the cylinder surface due to heating Mass spectra of acetone and methanol with CH 2 Cl 2 doping under Xe-lamp illumination S2

3 Supporting Figure S2. Time-of-flight mass spectra of the cations generated from acetone in N 2 before (A) and after (B) doping with CH 2 Cl 2 and that of the anions after doping with CH 2 Cl 2 (C) under Xe-lamp illumination. The partial flow rate of acetone and that of the dopant CH 2 Cl 2 in acetone was and molecules s -1, respectively. Time-of-flight mass spectra of the cations generated from methanol in N 2 before (D) and after (E) doping with CH 2 Cl 2 and those of the anions after doping with CH 2 Cl 2 (F) under Xe-lamp illumination. The partial flow rate of methanol and that of the dopant CH 2 Cl 2 in methanol was and molecules s -1, respectively. 3. Determination of the proton source Additional mass spectra observed in isotope experiments for determining the proton source are shown in Figures S2 4. All of the results support that the proton does not originate from dichloromethane but from water. S3

4 Supporting Figure S3. Time-of-flight mass spectra of the cations generated from methanol ( molecules s -1 ) after doping with CD 2 Cl 2 ( molecules s -1 ) (A) and CH 2 Cl 2 ( molecules s -1 ) (B-blue) followed by doping with D 2 O ( molecules s -1 ) (B-red) under Kr-lamp illumination. Mass peaks at m/z 33, 34, and 35 are assigned as (CH 3 OH)H +, (CH 3 OH)D + /(CH 3 OD)H +, and (CH 3 OD)D +, respectively. The ions (CH 3 OD)H + and (CH 3 OD)D + result from the hydrogen-exchange reaction between CH 3 OH and D 2 O, followed by ionization reaction. S4

5 Supporting Figure S4. Time-of-flight mass spectra of the cations generated from acetone ( molecules s -1 ) after doping with CD 2 Cl 2 ( molecules s -1 ) (A) and CH 2 Cl 2 ( molecules s -1 ) (B-blue) followed by doping with D 2 O ( molecules s -1 ) (B-red) under Xe-lamp illumination S5

6 Supporting Figure S5. Time-of-flight mass spectra of the cations generated from methanol ( molecules s -1 ) after doping with CD 2 Cl 2 ( molecules s -1 ) (A) and CH 2 Cl 2 ( molecules s -1 ) (B-blue) followed by doping with D 2 O ( molecules s -1 ) (B-red) under Xe-lamp illumination Enhancing effects of four chlorohydrocarbons on ion currents Additional materials on enhancing effects of four chlorohydrocarbons on ions currents are shown in Figures S5&6. The results reveal that CH 2 Cl 2 exhibited a more efficiently enhancing effect on the ion currents compared to the other three chlorohydrocarbons. The signal intensities increase almost linearly with the partial flow rate of CH 2 Cl 2 initially and reach a plateau gradually. The saturation of the CH 2 Cl 2 - dependent signal intensity may partially result from the insufficient pumping of the ion source system, leading to the collision loss of ions during ion immigration. In addition, the CH 2 Cl 2 -induced enhancing effect on the ion currents generated from the N 2 buffer gas, acetone in N 2, and methanol in N 2 are almost the same under the same kind of lamp illumination (as seen in Figures 5(C&D) and Figure S6(A)). This phenomenon indicates S6

7 that the product yield of ions is mainly determined by the quantity of the excited-state CH 2 Cl Supporting Figure S6. Doping effects of four chlorohydrocarbons on the intensities of the cation current generated from the N 2 buffer gas (A) and acetone in N 2 (B) under Xelamp illumination. The error bars of the data points were derived from the standard deviation of the three parallel experiments. S7

8 Supporting Figure S7. Doping effects of four chlorohydrocarbons on the intensities of the cation current generated from methanol in N 2 under Kr-lamp (A) and Xe-lamp (B) illumination. The error bars of the data points were derived from the standard deviation of the three parallel experiments CH 2 Cl 2 -dependent increase of protonated acetone and methanol The CH 2 Cl 2 -dependent increase of the signal intensities of protonated acetone and methanol under Kr- and Xe-lamp illuminations is shown in Figures S7. Like those of ion currents, the signal intensities of protonated acetone and methanol increase almost linearly with the partial flow rate of CH 2 Cl 2 initially and reach a plateau gradually. S8

9 Supporting Figure S8. Doping effects of CH 2 Cl 2 on the mass spectrometric signal intensities of the protonated acetone and methanol under Kr- and Xe-lamp illumination, respectively. Signal intensities of acetone and methanol were calculated by accumulating the total counts in the mass range 59 ± 0.5 and 33 ± 0.5, respectively. The acquisition time for each mass spectrum was 10 s Observations of the by-product CH 2 O The magnified mass spectra for showing the protonated by-product formaldehyde produced in the reaction are shown in Figure S8. Since acetone, during the photoionization process, produced a daughter ion with m/z 31 (shown in Figure 3 (A)) which overlapped the mass peak of protonated by-product of CH 2 Cl 2, (CH 2 O)H + (m/z 31), the cationic mass spectrum of acetone after doping with CD 2 Cl 2 was provided in Figure S8(C). The mass peak of (CD 2 O)H + with m/z 33 was observed, which was attributed to the protonated by-product of the CD 2 Cl 2 involved reaction. This result also indicates that S9

10 the group of CH 2 of the formed formaldehyde derived from CH 2 Cl 2. In the experiments, weak signals of (CH 2 O)H + at m/z 31 were found in the cation mass spectra in the presence of CH 2 Cl 2. and strong HCl Cl - signals at m/z 71, 73, and 75 were observed in the anion mass spectra with a large amount CH 2 Cl 2 doping. The weak (CH 2 O)H + signal was attributed to the low probability of the secondary ionization reaction process for the byproduct CH 2 O. For example, in the presence of CH 2 Cl 2 there were 10 7 signal counts of protonated acetone obtained with mass spectrometer from molecules s -1 of acetone. The total detection efficiency including ionization and ion transmission would be ~10-6. In the ionization reaction (at a maximum CH 2 Cl 2 concentration), CH 2 O was a by-product whose concentration was equal to protonated acetone, molecules s -1. Therefore, through the secondary ionization reaction of CH 2 O, the mass spectrometric signal intensity would be ~10 4 counts, which is consistent with the signal intensity observed in the experiment. The stronger HCl Cl - signal might be derived from the direct attachment of HCl with Cl Supporting Figure S9. The magnified mass spectra for showing the protonated byproduct formaldehyde produced in the reaction. Figure S8 shows the mass spectra of the cations generated from the N 2 buffer gas after doping with CH 2 Cl 2 ( molecules s -1 ) (A), methanol in N 2 after doping with CH 2 Cl 2 ( molecules s -1 ) (B), and acetone in N 2 after doping with CD 2 Cl 2 ( molecules s -1 ) (C) under Kr-lamp illumination Energy calculations Calculations of standard molar enthalpies of reactions (Δ r H m (g, 298 K)) for the two hypothetical processes, formation of ion pairs with (process I) and without (process II) reorganization of OH and CH 2 Cl radicals to form HCl and CH 2 O, is shown in Table S10

11 S1. Supporting Table S1. Calculations of standard molar enthalpies of reactions (Δ r H m (g, 298 K)) for the following two hypothetical processes. I. Ionization with reorganization of OH and CH 2 Cl raidcals to form HCl and CH 2 O. CH 2 Cl 2 + 2H 2 O + hv H + 3 O + Cl - + HCl + CH 2 O Δ r H m (g, 298 K) = Δ f H m (H + 3 O) + Δ f H m (Cl - ) + Δ f H m (HCl) + Δ f H m Kr lamp (CH 2 O) Δ f H m (CH 2 Cl 2 ) 2Δ f H m (H 2 O) PE Kr = kj mol -1 < 0 Δ r H m (g, 298 K) = Δ f H m (H + 3 O) + Δ f H m (Cl - ) + Δ f H m (HCl) + Δ f H m Xe lamp (CH 2 O) Δ f H m (CH 2 Cl 2 ) 2Δ f H m (H 2 O) PE Xe = kj mol -1 < 0 II. Ionization without reorganization of OH and CH 2 Cl raidcals CH 2 Cl 2 + 2H 2 O + hv H + 3 O + Cl - + HO + CH 2 Cl Δ r H m (g, 298 K) = Δ f H m (H + 3 O) + Δ f H m (Cl - ) + Δ f H m (HO) + Δ f H m Kr lamp (CH 2 Cl) Δ f H m (CH 2 Cl 2 ) 2Δ f H m (H 2 O) PE Kr = kj mol -1 > 0 Δ r H m (g, 298 K) = Δ f H m (H + 3 O) + Δ f H m (Cl - ) + Δ f H m (HO) + Δ f H m Xe lamp (CH 2 Cl) Δ f H m (CH 2 Cl 2 ) 2Δ f H m (H 2 O) PE Xe = kj mol -1 > 0 The calculation results show that without reorganization of OH and CH 2 Cl radicals, the calculated Δ r H m (g, 298 K) would be larger than zero. Proton and electron transfer could not occur under this condition. Moreover, if the binding energy for the formation of the first reaction complex was considered in the process II, by referring that the interaction energies of two neutral molecules via hydrogen bonds are smaller than dozens of kj mol -13, 1 the calculated Δ r H m (g, 298 K) for both situations adopted Kr and Xe lamps are still larger than zero. Related parameters used in the calculation as well as their derivations are provided as follows: PE Kr and PE Xe are single photon energies of Kr and Xe lamps, which were calculated from the wavelengths of main emission lines from excitation of Kr and Xe gases. The wavelengths of main and minor resonance lines for Kr lamp are nm S11

12 (78%) and nm (22%), and those for Xe lamp are nm (98%) and nm (2%). 2 The values adopted here were and nm for Kr and Xe lamps, corresponding to photon energies of and kj mol -1, respectively. Values of standard molar enthalpies of formation (Δ f H m (g, 298 K)) are listed as follows, which are directly derived from the National Institute of Standards and Technology (NIST) Chemistry WebBook. 3 Δ f H m (CH 2 Cl 2 ) = kj mol -1 Δ f H m (H 2 O) = kj mol -1 Δ f H m (HCl) = kj mol -1 Δ f H m (CH 2 O) = kj mol -1 Δ f H m (HO) = 39.0 kj mol -1 Δ f H m (H) = kj mol -1 Δ f H m (Cl) = kj mol -1 Values of Δ f H m (g, 298 K) for H + 3 O, Cl -, and CH 2 Cl radical are obtained indirectly with calculation by the following method. Δ f H m (H + 3 O, g) = Δ f H m (H, g) + IP(H) PA(H 2 O) + Δ f H m (H 2 O, g) = kj mol -1 Δ f H m (Cl -, g) = Δ f H m (Cl) EA(Cl) = kj mol -1 Where IP(H), PA(H 2 O), and EA(Cl) are the ionization potential of Hydrogen atom, the proton affinity of H 2 O, and the electron affinity of Chlorine atom. Their values are listed as follows: IP(H) = 1312 kj mol -1 3 PA(H 2 O) = 691 kj mol -1 3 EA(Cl) = kj mol -1 4 Δ f H m (CH 2 Cl) is calculated from the Δ r H m (g, 298 K) of the reaction: CH 2 Cl 2 Cl + CH 2 Cl Δ r H m (g, 298 K) = Δ f H m (Cl) + Δ f H m (CH 2 Cl) Δ f H m (CH 2 Cl 2 ) = kj mol -1 Where Δ r H m (g, 298 K) is obtained by theoretical calculation using Gaussian 09 program. 5 Geometry optimization and frequency analysis are conducted using the unrestricted hybrid density functional method UB3LYP/ G (d, p) basis set. Then, Δ f H m (CH 2 Cl) = kj mol -1 + Δ f H m (CH 2 Cl 2 ) Δ f H m (Cl) = 82.9 kj S12

13 Effects of gaseous H 2 O on the ion formation Figure S9 shows the effect of the extra doped H 2 O on the total ion current generated from CH 2 Cl 2 /H 2 O/acetone system. The experimental result indicates that extra doping of gaseous H 2 O (up to its saturated partial pressure) has little impact on the total quantity of cations generated in the ionization reaction. It should be noted that the ions include protonated water and its cluster, as well as acetone. We speculate that the quantity of the residual water in the system is already excessive for the reaction with the ion-pair excited state of CH 2 Cl 2 ([CH 2 Cl + -Cl - ] * ). The partial flow rate of the residual gaseous H 2 O in continuously sampled gas was estimated to molecules s -1 according to the impurity constituents of high-purity N 2 (containing 5 ppmv H 2 O). In this study, the yield rate of total excited-state CH 2 Cl 2 (mainly including ion-pair states and Rydberg states) in the ion source was calculated to be ~ molecules s -1 based on the highest partial flow rate of CH 2 Cl 2 ( molecules s -1 ), reported total absorption cross-section of CH 2 Cl 2 ( cm 2 ) at the wavelength nm (equal to the photon energy of 10.2 ev), 6 the photon flux of the Kr lamp ( photons cm -2 s -1 ), and the stay time of each CH 2 Cl 2 molecule in the ionizer ( s). The quantum yield of dissociated ionpair states [CH 2 Cl + -Cl - ] * is and that of binding ion-pair states [CH 2 Cl + -Cl - ] * has not been documented. 7 The effect of the H 2 O concentration on the quantity of total ions could be observed only when the residual H 2 O is reduced to an extremely low level, which cannot be measured exactly based on our experimental conditions at present. In addition, the effect of the decreased H 2 O on the H 3 O + (ion/s) generated from the residual H 2 O in N 2 has been performed, as shown in the following Figure A1. The residual H 2 O in N 2 was reduced by a drying tube which contained Magnesium rod and was heated to different temperatures (120, 180, and 240 ᵒC) to obtain the different residual H 2 O concentrations. The experimental results show that the amount of H 3 O + decreases with the decrease of residual H 2 O in N 2. S13

14 Supporting Figure S10. Effects of extra doped H 2 O on the cation current generated from acetone/ch 2 Cl 2 ( molecules s -1 ) under Kr-lamp illumination Supporting Figure S11. Doping effects of CH 2 Cl 2 on the mass spectrometric signal intensities of the H 3 O + generated from the residual H 2 O in N 2 under Kr-lamp illumination. 9. Dependence of photon intensities on methane pressures S14

15 The logarithmic decay of the photon intensity with the methane pressure in the light attenuation cell is shown in Figure S11. There are two groups of linear data observed apparently indicate that there is a minor amount of light with wavelengths longer than nm (the main output of the Kr lamp), but these light still can yield photoelectrons. Therefore, the light-power-dependence experiments are performed with the top ten photon flux datum points to avoid the large uncertainty in the lower photon flux Supporting Figure S12. The logarithmic decay of the photon intensity with the methane pressure in the light attenuation cell. 9. Chemicals In this study, acetone (Pesticide Grade, Fisher Scientific), methanol (A. R., Sinopharm), dichloromethane (99.9%, J&K), trichloromethane (A. R., Sinopharm), tetrachloromethane (A. R., Shanghai Xilong), CD 2 Cl 2 (99.6%+ atom % D, Acros), D 2 O (99.9% atom % D, J&K), H 18 2 O (97% atom % 18 O, Aladdin) were used. High-purity nitrogen (>99.999%) and Chloromethane (99.9%) were purphased from Beijing Haikeyuanchang Gas Co., Ltd and Chengdu Keyuan Gas Co., Ltd respectively. Krypton S15

16 (5%, v/v) and xenon (5%, v/v) with helium as balance gas as well as methane (99.9%) were purchased from Beijing Huayuan Gas Co., Ltd. 10. References 1. Rozas, I. On the nature of hydrogen bonds: an overview on computational studies and a word about patterns. Phys. Chem. Chem. Phys. 2007, 9 (22), Okabe, H. Intense Resonance Line Sources for Photochemical Work in the Vacuum Ultraviolet Region. J. Opt. Soc. Am. 1964, 54 (4), Hotop, H.; Lineberger, W. C. Binding energies in atomic negative ions. J. Phys. Chem. Ref. Data 1975, 4 (3), Gaussian 09, Revision A.02, M. J. Frisch et al., Gaussian, Inc., Wallingford CT, Vatsa, R. K.; Volpp, H. R. Absorption cross-sections for some atmospherically important molecules at the H atom Lyman-α wavelength ( nm). Chem. Phys. Lett. 2001, 340 (3 4), Simpson, M. J.; Tuckett, R. P. Vacuum-UV negative photoion spectroscopy of gasphase polyatomic molecules. Int. Re. Phys. Chem. 2011, 30 (2), S16

U N I T T E S T P R A C T I C E

South Pasadena AP Chemistry Name 8 Atomic Theory Period Date U N I T T E S T P R A C T I C E Part 1 Multiple Choice You should allocate 25 minutes to finish this portion of the test. No calculator should