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Previously developed technique of charge exchange ionization in a collision cell outside the ion source, which detects ions originating from the collision gas in the cell, was used to find long-lived excited electronic states of monosubstituted benzene cations. The technique is based on the criterion that charge exchange between polyatomic species is efficient only when the energy of reaction is close to zero or negative (ΔE≤0), or the exoergicity rule. The &Btilde; ²B[sub 2] states of chlorobenzene, bromobenzene, benzonitrile, and phenyl acetylene cations were found to have long lifetimes (10 microseconds or longer) while excited electronic states with long lifetime were not detected for fluorobenzene, iodobenzene, toluene, nitrobenzene, and styrene cations. The long-lived states found were those displaying well-resolved vibrational structures in the photoelectron spectra. In particular, these were the states generated by removal of an electron from the in-plane nonbonding p orbitals of halogens or in-plane π orbitals of the triple bonds. [ABSTRACT FROM AUTHOR]

Photodissociation of the methyl chloride ion has been investigated using mass-analyzed ion kinetic spectrometry (MIKES). The MIKE spectrum for the chlorine atom loss from the methyl chloride ion has been measured as a function of the laser polarization angle at 357, 488.0, and 514.5 nm. The anisotropy parameters and kinetic energy release distributions have been determined. At all the wavelengths used, an anisotropic dissociation (β=1.2) in the repulsive excited electronic state has been observed. Results from quantum chemical calculations carried out at the various levels suggest that the methyl chloride ion is excited to the first excited electronic state A˜, and dissociates repulsively in this state. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presence of benzene cation in a long-lived excited electronic state at ∼2.3 eV above the ground state was found through photodissociation kinetics and charge exchange ionization mass spectrometry. The lifetime of this state seems to be longer than 10 μs, maybe much longer. The experimental energy level of this state suggests that B˜ [sup 2]E[sub 2g] is the best candidate. The radiative transition from the latter state to the ground state, B˜ [sup 2]E[sub 2g]→X˜ [sup 2]E[sub 1g], is electric dipole forbidden. Then, a very long lifetime requires an inefficient radiationless decay of the state. This is in contrast with the very fast decay proposed previously to account for the lack of fluorescence from the B˜ [sup 2]E[sub 2g] state. The present finding opens the possibility of studying a new excited state chemistry. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photodissociation of the propargyl bromide molecular ion has been investigated using mass-analyzed ion kinetic energy spectrometry (MIKES). The MIKE spectra for the bromine loss has been measured as a function of the laser polarization angle at 357, 488.0, 514.5, and 607.5 nm. A convenient analytic method to treat the MIKE profile has been developed and the anisotropy parameters and kinetic energy release distributions (KERDs) have been determined by analyzing the experimental data. At all the wavelengths used, an anisotropic dissociation in the repulsive excited electronic state(s) has been observed. In addition, the statistical dissociation in the ground electronic state has been observed at 357 and 607.5 nm. Results from quantum chemical calculations carried out at the TDDFT/UB3LYP level using the 6-311++G** basis set will be discussed in relation to the nature of the repulsive excited electronic state involved. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]