FEMTOSECOND VIBRATIONAL DEPHASING OF THE CN STRETCHING IN ALKANENITRILES WITH LONG ALKYL CHAINS - DEPENDENCE ON THE CHAIN-LENGTH AND HYDROGEN-BONDING

Femtosecond time-resolved coherent anti-Stokes Raman scattering has been observed for the C=N stretching vibration of alkanenitriles (CnH2n+1CN, n=1-17). The vibrational dephasing rates (1/T2) observed for the neat alkanenitriles are proportional to the square root of the number of carbon atoms (n) in the alkyl chain. The dephasing rates observed for mixtures of the alkanenitriles with methanol (1 : 1 mole ratio) are about 30% faster than those for the corresponding neat alkanenitriles. Possible origins of this acceleration in the dephasing rate are discussed.