Dephasing times of the stretching vibration in liquid N2 and of the vibrons in the α and β crystalline phases

Abstract

Abstract Picosecond time-resolved CARS measurements have been performed on the stretching vibration in liquid N 2 , and on the vibrons in single crystals of N 2 in the α and β phases. Exponential decay was observed in the liquid and β phases. In the α phase the coherence decay could be described by an exponential and a Gaussian factor in the decay signal, corresponding to a homogeneous and an inhomogeneous contribution to the spectral width, respectively. The dephasing times ( T 2 /2) were found to range from 88 ps for the liquid phase to 1.2 ns for α-N 2 at 5.6 K. In contrast with theoretical predictions, the T g vibron decays at the same rate as the A g vibron, as seen from the beating pattern between the two modes. The factor group splitting between the two vibrons in α-N 2 was determined through analysis of the beating patterns, with a 0.005 cm -1 accuracy. A decrease of this splitting is observed with increasing temperature towards the α-β phase transition.