Spin−Orbit Coupling Effect and Intramolecular Orbital Interactions:  Penning Ionization of CH₂BrCl, CHBrCl₂, and CH₂BrCN by Collision with He*(2³S) Metastable Atoms

Abstract

He*(2 3 S) Penning ionization electron spectra (PIES) as well as He I ultraviolet photoelectron spectra have been measured for CH 2 BrCl, CHBrCl 2 , and CH 2 BrCN. For the lower ionization-potential bands, spin-orbit split states are assigned in the spectra for CH 2 BrCl and CH 2 BrCN, whereas valence-orbital, ionic states are assigned for CHBrCl 2 . These assignments are based on the fact that the intramolecular orbital interactions in CHBrCl 2 are much stronger than those in the other molecules, whereas the spin-orbit coupling effects predominate for the other two molecules. Collision energy dependence of partial Penning ionization cross sections and the PIES indicate that the magnitudes of the attractive interactions in the electron distribution regions of the lone pair orbitals (n) of the Cl and Br atoms and the N atom in the CN group and π CN orbitals are in a sequence of n N . n Br ∼ π CN > n Cl .

Toward elucidating the mechanism of femtosecond pulse shaping control in photodynamics of molecules by velocity map photoelectron and ion imaging

“…These peaks we assign to a five photon ionization process with a total excitation energy of 11.5 eV and the formation of CH 2 BrCl + ͑X AЈ͒ ground state and electronically excited CH 2 BrCl + ͑Ã AЉ͒ parent ion. Tian et al 43 observed these similar two electron peaks separated by about 0.33 eV. This total excitation energy is also very close to the fragmentation threshold of 11.509 eV of CH 2 Cl + +Br͑ 2 P 3/2 ͒, so we do not think that direct five-photon excitation produces much fragmentation, as we should see a near 0 eV photoelectron peak.…”

“…7, we show the location of the lowest energy levels in the CH 2 BrCl + parent ion and the CH 2 Cl + +Br͑ 2 P 3/2 , 2 P 1/2 ͒ fragmentation channels. Photoelectron spectroscopy experiments 43 reveal that just above threshold there are four photoelectron bands related to the CH 2 BrCl + cation and they were observed at 10.75, 11.08, and 11.79 eV ͑unresolved structure͒. The first two bands at 10.75 and 11.08 eV correspond to ionization of the bromine lone-pair electron and the level is split as a result of the strong spinorbit coupling in CH 2 BrCl + due to the Br atom.…”

“…3-5͒ to originate from excitation of the n y ͑Br, 8aЉ͒ and n x ͑Br, 22aЈ͒ CH 2 BrCl molecular lone-pair orbitals located at the Br-atom. 43,44,49 We use the molecular frame convention of Gonzalez and co-workers 49 labeling the Br-C-Cl plane as the xz-plane and the y-axis perpendicular to the molecular C s plane.…”

Electron momentum spectroscopy of the highest occupied molecular orbitals of chlorobromomethane

“…The ordering of valence orbitals is adopted from the PES of Tian et al [3]. Figure 1 shows one of the ionization energy spectra of CH 2 BrCl over the energy range from 5 eV to 30 eV measured at azimuthal angles φ = 7°by EMS.…”

“…synchrotron radiation light sources, Penning ionization electron spectra (PIES) [3] using He*(2 3 S) metastable atoms and photodissociation dynamics [5] using laser pulses. To our best knowledge, no electron momentum spectroscopy measurement on CH 2 BrCl has been reported so far.…”