Measurement of Internal Energies by Hot Ultraviolet Absorption Spectroscopy: Spectra of Excited Azulene Molecules

Article abstract of DOI:10.1021/j100267a039

The gas-phase absorption spectrum of azulene in the wavelength range λ = 220-300 nm has been measured in shock waves between 600 and 1750 K.Combined with the room-temperature spectrum, a dependence of the absorption coefficients ε(λ) on the average thermal energy over the range 10-420 kJ mol^-1 is established.The "canonically hot" UV spectra are compared with "microcanonically hot" UV spectra obtained by laser excitation of azulene at 337 and 308 nm, corresponding to excitation energies of 367 and 400 kJ mol^-1. "Microcanonically hot" and "canonically hot" absorption spectra agree perfectly when the average internal energies of the ensembles are the same.This experimental observation is rationalized.Various applications of hot UV absorption spectroscopy in chemical kinetics are reviewed.