Probing the spectral diffusion of vibrational transitions of OCN- and SCN- in methanol by three-pulse infrared photon echo spectroscopy

Three-pulse infrared photon echo spectroscopy has been used to determine the correlation function of the fluctuations of the vibrational frequencies of OCN- and SCN- in methanol. The correlation functions of the antisymmetric stretching modes for these two ions are fitted with a double exponential function with time constants of around 100 fs and 4 ps. The amplitude of the fluctuations for SCN- is found to be greater than that for OCN-. We discuss the difference of the spectral diffusion processes between OCN- and SCN- in methanol.