A statistical analysis of the ν₂ and ν₃ modes of methyl iodide

Abstract

The ν₂ and ν₃ Raman-band profiles of methyl iodide have been carefully measured as a function of temperature. Both I _iso(ω) and I _VH(ω) profiles have been extracted and Fourier transformed to provide the corresponding autocorrelation functions. The second moments of the bands have been determined to ±15 per cent. The vibrational-correlation and memory functions have been analysed by a memory-function modelling procedure and by an autoregressive time-series analysis. In order to separate the effects of resonant vibrational energy transfer and dipolar interactions from pure dephasing processes, CH₃I has been studied in the solvents CD₃I, CH₃F, n-pentane, and CS₂. Evidence is presented for intermolecular vibration-rotation interaction in the ν₂ and ν₃ modes. A large contribution to the dephasing by resonant vibrational energy transfer has been found for both modes, with dipole-dipole interaction contributing a lesser amount. Our analysis suggests that static inhomogeneity contributes a constant 8–10 cm^-2 to the second moment.