The photodissociation dynamics of ICl is studied at 304 nm by state-selective photofragment translational spectroscopy. Velocity distributions, anisotropy parameters, and relative quantum yields are obtained for the ground I(2P3/2) and spin−orbit excited state I*(2P1/2) iodine atoms, which are produced from photodissociation of ICl at this wavelength. Two sharp velocity distributions are observed for the I channel, suggesting the existence of two dissociation pathways that correlate with ground state iodine formation. Based on the expected translational energy release and the energy separation between those peaks, the two distributions are assigned to dissociation of ICl to I(2P3/2) + Cl(2P3/2) and to I(2P3/2) + Cl*(2P1/2); the former channel appears at higher translational energy. The distribution of I* also shows two strong peaks, indicating that there are two dominant channels for the formation of I* atoms at this wavelength which we assign to the dissociation of ICl forming I*(2P1/2) + Cl(2P3/2) and I*(2P1/2) + Cl*(2P1/2), respectively. The quantum yield of I*(2P1/2) is determined to be 0.30, indicating that the formation of ground state iodine is clearly the favored dissociation channel at 304 nm. The observed anisotropy in the angular distribution of dissociation products (β) indicates that the I* + Cl and I* + Cl* channels are formed predominantly from the parallel transition (β = 1.7 for both channels) while the I + Cl and I + Cl* products are formed mainly from perpendicular transitions (β = −0.5). The decrease in the anisotropy parameter of the I formation channels from their limiting value of −1 is attributed to the presence of more than one path for the formation of I + Cl/Cl* photoproducts with opposite polarization for their absorbing transitions. The possible excited state dynamics, which give the observed results, are discussed in terms of the previously proposed energy correlation diagram for ICl.

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Proton-transfer reactions that proceed within methanol cluster ions were studied using an electron impact time-offlight mass spectrometer. When CH,OH seeded in helium is expanded and ionized by electron impact, the protonated species, (CH,OH),H+, are the predominant cluster ions in the low-mass region. In CH,OD clusters, both (CH,OD),H+ and (CH,OD),D+ ions are observed. The ion abundance ratios, (CH30D),H+/(CH30D),D+, show a tendency to decrease as the methanol concentration increases, which is apparently related to the cluster structure and reaction energetics. The results suggest that the effective formation of (CH,OD),H+ ions at low concentration of CH,OD in the expansion is the result of the relatively facile rotation of methanol molecules within the smaller clusters that tend to form at low CH,OD concentration. Ab initio molecular orbital calculations were carried out to investigate the rearrangement and dissociative pathways of ionized methanol dimer. Ion-neutral complexes, [CH,OH,+-.O(H)CH,] and [CH,OH,+-OCH,I, are found to play an important role in the lowenergy pathways for production of CH30H2+ + CH,OH (and OCH,) from ionized methanol dimer.

KCT0001502.