Solvation effects on reactive intermediates: The benzyl radical and its clusters with Ar, N2, CH4, C2H6, and C3H8

Abstract

Mass resolved excitation spectra are presented for the benzyl radical and its clusters with Ar, N2, CH4, C2H6, and C3H8. The cluster spectra exhibit small redshifts (≤50 cm−1) relative to the unclustered benzyl radical for the D1(1 2A2)←D0(1 2B2) and D2(2 2B2)←D0(1 2B2) electronic transition regions. A unique set of low energy van der Waals modes is observed for these clusters for each excited electronic state investigated. The cluster spectra also reveal significant vibronic coupling between the two excited electronic states of the benzyl radical, as evidenced by a single vibrational predissociation threshold for each cluster. Ab initio calculations are performed on the benzyl radical to examine excited electronic state structure, predict transition energies, estimate ionization energy, and determine partial atomic charges in the electronic states of interest. The resulting partial charges are used in empirical atom–atom potential energy calculations to aid in the understanding of cluster spectroscopic shifts, binding energies, and van der Waals modes.

IR + vacuum ultraviolet (118 nm) nonresonant ionization spectroscopy of methanol monomers and clusters: Neutral cluster distribution and size-specific detection of the OH stretch vibrations

“…The data acquisition scheme for infrared spectroscopy is similar to that used to record the resonance-enhanced multiphoton ionization ͑REMPI͒ spectroscopy described in detail in our previous publications. 40,41…”

The Benzyl Radical-Ethylene Molecular Cluster: An Example of Electronic-State Mediation of Chemical Reactivity

“…The reaction exothermicity is presumably to be transformed into internal (thermal) energy of the product complex. Three pieces of experimental evidence are found for this cluster system which support theoccurrenceof an excited-state photochemical addition reaction: (1) Frank-Condon broadened excitation spectrum for the cluster, (2) reduced (by more lo3 cm-l) ionization energy compared to that observed for both the unclustered benzyl radical and the benzyl radicallethane cluster, and (3) a roughly 7000-cm-' apparent "binding energy" for the excited-state benzyl radical/ethylene cluster.…”

Solvation of the methoxy radical in small clusters

“…21,22 Briefly, the experiments have been carried out in a stainless steel vacuum chamber at a pressure of ϳ10 Ϫ4 Torr. To produce the clusters, CH 3 OH vapor is mixed with He carrier gas and the clustering agent.…”

“…van der Waals complexes containing even simple radicals are often difficult to model because the nature of the interactions between the radical and the solvent molecules can be very specific and solvent molecule dependent; for example, the CH 3 O/Ar cluster interactions should have major contributions from dispersion and charge transfer terms, 20 the CH 3 O/N 2 cluster interactions should have major contributions from quadrupole terms; 21 the CH 3 O/CF 4 cluster interactions should have major contributions from Coulombic terms, and the CH 3 O/CH 4 clusters interactions can have contributions from reaction processes. A unique form, into which these various detailed interactions can be cast, is often difficult to find.…”