Combined Vacuum Ultraviolet Laser and Synchrotron Pulsed Field Ionization Study of CH₂BrCl.
- Tsinghua Univ., Beijing (China)
- City Univ., Hong Kong (China)
- Univ. of California, Davis, CA (United States)
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.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States), Environmental Molecular Sciences Laboratory (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 921388
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 18 Vol. 126; ISSN JCPSA6; ISSN 0021-9606
- Publisher:
- American Institute of Physics (AIP)
- Country of Publication:
- United States
- Language:
- English
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