Comparison of experiment and theory for the resonance Raman spectrum of I2 in solution. I. The Raman excitation profile of I2 in n-hexane

The absolute Raman excitation profiles (REPs) of the fundamental and first two overtones of I2 dissolved in n-hexane were determined with excitation frequencies from 15 000 to 22 000 cm−1. Calculations for both the absorption spectrum and the REPs were performed and the results compared to the experimental results. Good agreement was found using gas phase potentials for the A, B, and B″ states and a ground state potential modified to reproduce the observed anharmonicity of the I2 vibrations in n-hexane. The homogeneous linewidth in the excited electronic states is Γ=15–20 cm−1 (HWHM), which corresponds to a T2 of ≊0.3 ps. The spectra have an inhomogeneous component of 400 cm−1 (HWHM). Separate calculations demonstrate the effects of the excited electronic states individually and demonstrate the importance of the interference terms in the REP. Calculations also demonstrate the sensitivity of the depolarization ratio to the contributions of the various excited electronic states. The index of refraction corrections required in solution are close to those expected.