Vacuum ultraviolet photodissociation spectroscopy of CH3CN, CD3CN, CF3CN and CH3NC

Abstract

The results obtanined from a study of the vibrational and rotational energy disposals in the vacuum ultraviolet photodissociation of CH₃CN, CD₃CN, CF₃CN and CH₃NC have been explained in terms of a statistical partitioning (consistent with dissociation from a long-lived intermediate via a “loose” transition state) together with the restrictions imposed by conservation of overall energy and angular momentum. The vacuum ultraviolet absorption spectra of the four molecules have been assigned in an attempt to identify the character of the photoexcited states at each photolysis wavelength. The observed distributions are in marked contrast to those obtained in the photodissociation of the simpler cyanogen halides from comparable excited states.

The following bond dissociation energies were obtained through an analysis of the rotational energy disposal, D(CH₃—CN)= 517 ± 3, D(CD₃—CN)= 515 ± 3, D(CF₃—CN)= 473 ± 3, D(CH₃—NC)= 430 ± 8 Kj MOL ^–1, to yeld ΔH^°_f0 values in good agreement with previous measurments.