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Title: Combined Vacuum Ultraviolet Laser and Synchrotron Pulsed Field Ionization Study of CH₂BrCl.

Abstract

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The pulsed field ionization-photoelectron (PFI-PE) spectrum of bromochloromethane (CH₂BrCl) in the region of 85 320–88 200 cm -1 has been measured using vacuum ultraviolet laser. The vibrational structure resolved in the PFI-PE spectrum was assigned based on ab initio quantum chemical calculations and Franck-Condon factor predictions. At energies 0–1400 cm ⁻1 above the adiabatic ionization energy (IE) of CH₂BrCl, the Br–C–Cl bending vibration progression (v₁⁺=0–8) of CH₂BrCl⁺ is well resolved and constitutes the major structure in the PFI-PE spectrum, whereas the spectrum at energies 1400–2600 cm -1 above the IE(CH₂BrCl) is found to exhibit complex vibrational features, suggesting perturbation by the low lying excited CH₂BrCl⁺(A²A") state. The assignment of the PFI-PE vibrational bands gives the IE(CH₂BrCl) =85 612.4±2.0 cm -1 (10.6146±0.0003 eV) and the bending frequencies v₁⁺(a₁')=209.7±2.0 cm -1 for CH₂BrCl⁺(X²A'). We have also examined the dissociative photoionization process, CH₂BrCl +hv→CH₂Cl ++Br +e -, in the energy range of 11.36–11.57 eV using the synchrotron based PFI-PE-photoion coincidence method, yielding themore » 0 K threshold or appearance energy AE(CH₂Cl⁺)=11.509±0.002 eV. Combining the 0 K AE(CH₂Cl⁺) and IE(CH₂BrCl) values obtained in this study, together with the known IE(CH₂Cl), we have determined the 0 K bond dissociation energies (D 0) for CH₂Cl+–Br (0.894±0.002 eV) and CH₂Cl–Br (2.76±0.01 eV). We have also performed CCSD(T, full)/complete basis set (CBS) calculations with high-level corrections for the predictions of the IE(CH₂BrCl), AE(CH₂Cl +), IE(CH₂Cl), D0(CH₂Cl +–Br), and D0(CH₂Cl–Br). The comparison between the theoretical predictions and experimental determinations indicates that the CCSD(T, full)/CBS calculations with high-level corrections are highly reliable with estimated error limits of <17 meV.« less

Authors:
 [1];  [1];  [1];  [2];  [3];  [3];  [3];  [3]
  1. Tsinghua Univ., Beijing (China)
  2. City Univ., Hong Kong (China)
  3. Univ. of California, Davis, CA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
921388
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 126; Journal Issue: 18
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; BENDING; COINCIDENCE METHODS; DISSOCIATION; ENERGY RANGE; IONIZATION; LASERS; PHOTOIONIZATION; SYNCHROTRONS; VIBRATIONAL STATES; Environmental Molecular Sciences Laboratory

Citation Formats

Li, Juan, Yang, Jie, Mo, Yuxiang, Lau, Kai Chung, Qian, X M, Song, Y, Liu, Jianbo, and Ng, Cheuk-Yiu. Combined Vacuum Ultraviolet Laser and Synchrotron Pulsed Field Ionization Study of CH₂BrCl.. United States: N. p., 2007. Web. doi:10.1063/1.2730829.
Li, Juan, Yang, Jie, Mo, Yuxiang, Lau, Kai Chung, Qian, X M, Song, Y, Liu, Jianbo, & Ng, Cheuk-Yiu. Combined Vacuum Ultraviolet Laser and Synchrotron Pulsed Field Ionization Study of CH₂BrCl.. United States. doi:10.1063/1.2730829.
Li, Juan, Yang, Jie, Mo, Yuxiang, Lau, Kai Chung, Qian, X M, Song, Y, Liu, Jianbo, and Ng, Cheuk-Yiu. Fri . "Combined Vacuum Ultraviolet Laser and Synchrotron Pulsed Field Ionization Study of CH₂BrCl.". United States. doi:10.1063/1.2730829.
@article{osti_921388,
title = {Combined Vacuum Ultraviolet Laser and Synchrotron Pulsed Field Ionization Study of CH₂BrCl.},
author = {Li, Juan and Yang, Jie and Mo, Yuxiang and Lau, Kai Chung and Qian, X M and Song, Y and Liu, Jianbo and Ng, Cheuk-Yiu},
abstractNote = {The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The pulsed field ionization-photoelectron (PFI-PE) spectrum of bromochloromethane (CH₂BrCl) in the region of 85 320–88 200 cm-1 has been measured using vacuum ultraviolet laser. The vibrational structure resolved in the PFI-PE spectrum was assigned based on ab initio quantum chemical calculations and Franck-Condon factor predictions. At energies 0–1400 cm⁻1 above the adiabatic ionization energy (IE) of CH₂BrCl, the Br–C–Cl bending vibration progression (v₁⁺=0–8) of CH₂BrCl⁺ is well resolved and constitutes the major structure in the PFI-PE spectrum, whereas the spectrum at energies 1400–2600 cm-1 above the IE(CH₂BrCl) is found to exhibit complex vibrational features, suggesting perturbation by the low lying excited CH₂BrCl⁺(A²A") state. The assignment of the PFI-PE vibrational bands gives the IE(CH₂BrCl) =85 612.4±2.0 cm-1 (10.6146±0.0003 eV) and the bending frequencies v₁⁺(a₁')=209.7±2.0 cm-1 for CH₂BrCl⁺(X²A'). We have also examined the dissociative photoionization process, CH₂BrCl+hv→CH₂Cl++Br+e-, in the energy range of 11.36–11.57 eV using the synchrotron based PFI-PE-photoion coincidence method, yielding the 0 K threshold or appearance energy AE(CH₂Cl⁺)=11.509±0.002 eV. Combining the 0 K AE(CH₂Cl⁺) and IE(CH₂BrCl) values obtained in this study, together with the known IE(CH₂Cl), we have determined the 0 K bond dissociation energies (D0) for CH₂Cl+–Br (0.894±0.002 eV) and CH₂Cl–Br (2.76±0.01 eV). We have also performed CCSD(T, full)/complete basis set (CBS) calculations with high-level corrections for the predictions of the IE(CH₂BrCl), AE(CH₂Cl+), IE(CH₂Cl), D0(CH₂Cl+–Br), and D0(CH₂Cl–Br). The comparison between the theoretical predictions and experimental determinations indicates that the CCSD(T, full)/CBS calculations with high-level corrections are highly reliable with estimated error limits of <17 meV.},
doi = {10.1063/1.2730829},
journal = {Journal of Chemical Physics},
number = 18,
volume = 126,
place = {United States},
year = {Fri May 11 00:00:00 EDT 2007},
month = {Fri May 11 00:00:00 EDT 2007}
}
  • No abstract is available for this journal article at this time.
  • Here, we report on the successful implementation of a high-resolution vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) detection method for the study of unimolecular dissociation of quantum-state- or energy-selected molecular ions. As a test case, we have determined the 0 K appearance energy (AE 0) for the formation of methylium, CH 3 +, from methane, CH 4, as AE 0 (CH 3 +/CH 4) = 14.32271 ± 0.00013 eV. This value has a significantly smaller error limit, but is otherwise consistent with previous laboratory and/or synchrotron-based studies of this dissociative photoionization onset. Furthermore, the sum of the VUV lasermore » PFI-PI spectra obtained for the parent CH 4 + ion and the fragment CH 3 + ions of methane is found to agree with the earlier VUV pulsed field ionization-photoelectron (VUV-PFI-PE) spectrum of methane, providing unambiguous validation of the previous interpretation that the sharp VUV-PFI-PE step observed at the AE 0 (CH 3 +/CH 4) threshold ensues because of higher PFI detection efficiency for fragment CH 3 + than for parent CH 4 +. This, in turn, is a consequence of the underlying high- n Rydberg dissociation mechanism for the dissociative photoionization of CH 4, which was proposed in previous synchrotron-based VUV-PFI-PE and VUV-PFI-PEPICO studies of CH 4. The present highly accurate 0 K dissociative ionization threshold for CH 4 can be utilized to derive accurate values for the bond dissociation energies of methane and methane cation. For methane, the straightforward application of sequential thermochemistry via the positive ion cycle leads to some ambiguity because of two competing VUV-PFI-PE literature values for the ionization energy of methyl radical. The ambiguity is successfully resolved by applying the Active Thermochemical Tables (ATcT) approach, resulting in D 0 (H-CH 3) = 432.463 ± 0.027 kJ/mol and D 0(H-CH 3 +) = 164.701 ± 0.038 kJ/mol.« less
  • The vacuum ultraviolet (VUV) pulsed field ionization photoelectron (PFI-PE) spectra for CH{sub 3}SH and CH{sub 3}CH{sub 2}SH have been obtained near their ionization thresholds. Using a semiempirical simulation scheme, we have obtained satisfactory fits to fine structures resolved in the VUV-PFI-PE spectra, yielding accurate ionization energies of 76thinsp256.3{plus_minus}2.9thinspcm{sup {minus}1} (9.454thinsp58{plus_minus}0.000thinsp36thinspeV) and 74thinsp948.7{plus_minus}2.9thinspcm{sup {minus}1} (9.292thinsp46{plus_minus}0.000thinsp36thinspeV) for CH{sub 3}SH and CH{sub 3}CH{sub 2}SH, respectively. {copyright} {ital 1998 American Institute of Physics.}
  • The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. By preparing methyl bromide (CH₃Br) in selected rotational levels of the CH₃Br(X˜ 1A1; V1 = 1) state with infrared (IR) laser excitation prior to vacuum-ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) measurements, we have observed rotationally resolved photoionization transitions to the CH₃Br⁺(X˜ 2E3/2; V1 + = 1) state, where V1 and V1 + are the symmetric C-H stretching vibrational modemore » for the neutral and cation, respectively. The VUV-PFI-PE origin band for CH₃Br⁺(X˜ 2E3/2) has also been measured. The simulation of these IR-VUV-PFI-PE and VUV-PFI-PE spectra have allowed the determination of the V1 + vibrational frequency (2901.8 ( 0.5 cm-1) and the ionization energies of the origin band (85 028.3 ( 0.5 cm-1) and the V1 + ) 1 r V1 ) 1 band (84 957.9 ( 0.5 cm-1).« less
  • The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. By using a high-resolution single mode infrared-optical parametric oscillator laser to prepare CH₃I in single (J,K) rotational levels of the v1 (symmetric C–H stretching) =1 vibrational state, we have obtained rovibrationally resolved infrared–vacuum ultraviolet–pulsed field ionization–photoelectron (IR-VUV-PFI-PE) spectra of the CH₃I⁺X˜ 2E 3/2 ;v 1 +=1;J + ,P +) band, where (J,K) and (J + ,P +) represent the respectivemore » rotational quantum numbers of CH₃I and CH₃I⁺. The IR-VUV-PFI-PE spectra observed for K=0 and 1 are found to have nearly identical structures. The IR-VUV-PFI-PE spectra for (J,K)=(5,0) and (7, 0) are also consistent with the previous J-selected IR-VUV-PFI-PE measurements. The analysis of these spectra indicates that the photoionization cross section of CH₃I depends strongly on |ΔJ⁺|=|J⁺-J| but not on J and K. This observation lends strong support for the major assumption adopted for the semiempirical simulation scheme, which has been used for the simulation of the origin bands observed in VUV-PFI-PE study of polyatomic molecules. Using the state-to-state photoionization cross sections determined in this IR-VUV study, we have obtained excellent simulation of the VUV-PFI-PE origin band of CH₃I +(X˜ 2E3/2), yielding more precise IE(CH₃I)=76 930.7±0.5 cm -1 and v 1 +=2937.8±0.2 cm -1.« less