Collisional energy transfer of vibrationally highly excited molecules. V. UV absorption study of azulene

TLDR

Vibrationally highly excited azulene (〈E〉≈30 600 cm⁻¹) was produced by N₂ laser excitation and its stepwise collisional deactivation with 23 inert bath gases was monitored by time‑resolved hot UV absorption at 290 nm, enabling extraction of average energy transferred per collision via calibrated absorption curves. The study found that the average energy transferred per collision, 〈ΔE〉, depends only weakly on excitation energy above 10 000 cm⁻¹, but rises more steeply at lower energies, and these results are compared with previous IR emission data on azulene.

Abstract

Vibrationally highly excited azulene molecules in the electronic ground state (excitation energy 〈E〉=30 600 cm−1) were produced by excitation with a N2 laser. The stepwise deactivation of the excited molecules in collisions with a variety of 23 inert bath gases was monitored by time-resolved hot UV absorption spectroscopy at 290 nm. Using previously determined calibration curves of the absorption coefficient at 290 nm as a function of the excitation energy 〈E〉, energy-loss curves 〈E(t)〉 were recorded and analyzed with respect to the average energies 〈ΔE〉 transferred per collision. The dependencies of 〈ΔE〉 on the excitation energy 〈E〉 were derived. In most cases, 〈ΔE〉 was found to be only weakly dependent on 〈E〉 above 10 000 cm−1, whereas a stronger rise with energy became apparent only at lower energies. A comparison with earlier IR emission experiments on the azulene system is given.