title: Combined vacuum ultraviolet laser and synchrotron pulsed field ionization study of CH2BrCl.
abstract: 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 (nu1+=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+(A 2A") 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 nu1+(a1')=209.7+/-2.0 cm-1 for CH2BrCl+(X2A'). We have also examined the dissociative photoionization process, CH2BrCl+hnu-->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.
authors.affiliation: Key Laboratory for Atomic and Molecular Nanosciences, Department of Physics, Tsinghua University, Beijing 10084, China.
authors.forename: Juan
authors.initials: J
authors.lastname: Li
authors.forename: Jie
authors.initials: J
authors.lastname: Yang
authors.forename: Yuxiang
authors.initials: Y
authors.lastname: Mo
authors.forename: K C
authors.initials: KC
authors.lastname: Lau
authors.forename: X M
authors.initials: XM
authors.lastname: Qian
authors.forename: Y
authors.initials: Y
authors.lastname: Song
authors.forename: Jianbo
authors.initials: J
authors.lastname: Liu
authors.forename: C Y
authors.initials: CY
authors.lastname: Ng
mesh_terms: D003198:Computer Simulation; D006846:Hydrocarbons, Halogenated / Q000737:chemistry* / Q000528:radiation effects*; D007477:Ions; D007834:Lasers; D008956:Models, Chemical; D008958:Models, Molecular; D017356:Synchrotrons; D014466:Ultraviolet Rays; D014618:Vacuum
chemical_list: D006846:Hydrocarbons, Halogenated; D007477:Ions; C006811:bromochloromethane