OVERTONE VIBRATIONAL DEPHASING OF CHLOROFORM STUDIED BY HIGHER-ORDER NONLINEAR SPECTROSCOPY

Vibrational dephasing of the overtone bands of chloroform and its deut erated analogue has been studied by higher-order nonlinear spectroscop y. The overtone signals of v = 2 and 3 are based on the fifth-and seve nth-order optical nonlinearity, respectively. The overtone vibrational dephasing signals as well as the fundamental ones are represented wel l by a single-exponential function. These dephasing signals are not ex plained by the stochastic theory with a time correlation function havi ng a Gaussian or exponential character. Effects of resonant transfer a nd population relaxation are found not to be important for the deviati on from the theoretical prediction. It is suggested that polyatomic na tures of the molecule such as off-diagonal anharmonicity or coupling w ith combination bands may be responsible for this deviation.