Effects of inhomogeneity in the infrared photodissociation spectra of (C2H4)2, C2H4⋅HF, and C2H4⋅HCl

Abstract

A general multilevel band shape model for describing predissociation spectra is presented. The model is applicable to systems of noninteracting molecules for which the predissociation rate is greater than the Rabi frequency. The multilevel band shape formula is used to analyze previously reported results for (C2H4)2, C2H4⋅HF, and C2H4⋅HCl. Using a reasonable set of molecular constants two apparently contradictory band shape measurements of the (C2H4)2 ν7 vibrational predissociation transition are shown to be in agreement. The anomalous width of the high power pulsed band shape measurement is attributed to orientational inhomogeneity of a hybrid band. Band shape simulations of C2H4⋅HF and C2H4⋅HCl indicate that the former spectrum is affected by rotational substructure while the latter is not. Other sources of inhomogeneity, including Fermi resonance, are discussed in terms of their effects on band shapes and intensities.