PNNL

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 (?1?=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 ?1?(a1')=209.7±2.0 cm-1 for CH2BrCl?(X²A'). We have also examined the dissociative photoionization process, CH2BrCl+h??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