UV absorption spectra of vibrationally highly excited toluene molecules

Abstract

Vibrationally highly excited toluene molecules with an energy of 52 000 cm⁻¹ have been prepared by UV laser excitation and subsequent isomerization of the isomer cycloheptatriene. The UV absorption spectrum of the toluene, whose vibrational energy would correspond to the average energy of thermal molecules at 2800 K, has been measured over the range 210–270 nm. It is compared with the UV spectrum of thermal molecules heated in shock waves up to 1800 K. All spectra, corresponding either to microcanonical or canonical energy distributions, can be represented by a modified Sulzer–Wieland equation. It is concluded that the absorption coefficients can be expressed to a first approximation by the average energy of the excited molecules independent of their energy distribution.