An analysis of the vibrational structure of the UV absorption spectrum of methacryloyl chloride vapor

The vibrational structure of the UV absorption spectrum of acryloyl chloride vapor was analyzed to obtain detailed information about the torsional vibration levels of the trans and cis isomers in the ground (S0) and excited (S1) electronic states. The spectrum contained 114 absorption bands of which ∼90% were assigned. The 0-0 transition frequencies of the trans and cis acryloyl chloride isomers were determined. Several Deslandres tables for torsional vibrations from the 0–0 transition frequencies and local origins corresponding to the fundamental frequencies of two isomeric molecule forms in both electronic states were constructed. The corresponding systems of torsional vibration levels were determined, and the harmonic frequencies θe and anharmonicity coefficients x11 of the trans and cis isomers were calculated. The torsional vibration levels in the ground electronic state obtained from the vibrational structure of the UV spectrum are compared with those determined using the Fourier spectrum. The 0–3 torsional transition of the trans isomer was found to be displaced because of Fermi resonance with a fundamental frequency.