We describe in detail a new method for solving the coupled linear differential equations which appear in the theoretical statement of many types of scattering phenomena. Combining the speed advantage of propagation methods with the inherent stability of R‐matrix methods, this method is fast and is unaffected by exponential growth of closed channels. We describe the propagation of the R‐matrix in terms of a collinear reactive scattering problem, and provide numerical results for several systems, clearly demonstrating the speed, stability, and accuracy of this method.

An R matrix approach to the solution of coupled equations for atom–molecule reactive scattering

Intracavity cw dye laser techniques incorporating photoacoustic detection have been used to measure visible absorption spectra of gas phase benzene (C6H6 and deuterated analogues C6H5D, p‐C6H2D4, and C6HD5). The prominent spectral features are attributable to CH stretch overtones that correspond to highly localized (’’bond‐selective’’) excitations of individual CH oscillators. These features have broad (∼100 cm−1 FWHM) Lorentzian line shapes that narrow as a function of increasing vibrational energy for most isotopic species. A simple model is presented to interpret the broad line shapes and their energy dependence as a manifestation of intramolecular V→V′ (vibration‐to‐vibration) energy redistribution and/or dephasing processes that occur rapidly (on 5×10−14 sec time scales), but nonstatistically, in isolated benzene and other polyatomic molecules.

Intramolecular rate processes in highly vibrationally excited benzene

Energy dependence of electronic relaxation processes in polyatomic molecules

Radiationless transitions in molecules

Flash photolysis of gaseous benzene has been carried out with a KrF laser (248.4 nm) as an excitation source. Two new transients have been detected, one of which has a structured absorption in the wavelength region from 235 to 260 nm. It has a rise time of 80 ns and a long decay time (≳25 μs). The precursor of this transient has also been detected. It appears as a shoulder at 225 nm and has a lifetime of 80 ns. This species is postulated to be a highly excited vibrational state of the ground electronic state, namely, a hot benzene molecule. This species is quenched by ground state benzene as well as by 12 different foreign gases, including oxygen and nitrogen, which have similar quenching rates. The decay of the hot benzene is accompanied by an increase in the temperature of the sample, which leads in turn to formation of the species with the structured absorption. The temperature of the equilibrated sample was determined by comparing the thermalized spectra in the nanosecond time scale with the steady‐st...

Michael G. Prais

Papers

Nonradiative decay processes in benzene