Conformational Dependence of Intramolecular Vibrational Energy Redistribution in the EthylenicCH2 Stretch Fundamental of Allyl Fluoride

Abstract

The high-resolution (6 MHz) infrared spectra of the asymmetric ethylenic hydride stretches of both cis and gauche allyl fluoride have been measured. Rotational assignments of the eigenstates are made using the ground-state microwave-infrared double-resonance capabilities of an electric resonance optothermal spectrometer (EROS). The cis vibrational band near 3114 cm-1 is characterized by sparse, narrow IVR multiplets resulting from weak Coriolis or cross conformer interactions between the vibrational bath states. The IVR lifetime of the cis vibrational band is approximately 2 ns (2000 ps). The gauche vibrational band near 3100 cm-1 is qualitatively and quantitatively quite different from the cis band. The gauche band is characterized by significantly fragmented IVR multiplets with an average IVR lifetime of about 90 ps. The measured anharmonic state density of the gauche band is about 30 states/cm-1. The disagreement between the measured state densities of the gauche vibrational band and the calculated val...