REAL-TIME PURSUIT OF CRYSTAL-GROWTH BY MILLISECOND TIME-RESOLVED MULTICHANNEL FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

The surface (about 130 molecular layers) of an oriented thin crystal o f decanoic acid was subjected to sudden melting by a laser-induced tem perature jump (T-jump) and the process of subsequent crystal re-growth was monitored by millisecond time-resolved multichannel Fourier trans form infrared spectroscopy. The gauche-trans structural change of the alkane part of the molecule has been probed by the CR stretch bands in the 2800-3000 cm(-1) region. The change in the molecular orientation has been detected by the OH stretch band around 3065 cm(-1). The recov ery curves for the CH2 antisymmetric stretch and the OH stretch bands are markedly different from each other in the first 200 ms, suggesting that the gauche-trans structural changes precedes the crystal re-grow th. After 500 ms, the recovery curves become identical, This result me ans that the rate of the gauche to the trans structural change is equa l to the rate of the recovery of the molecular orientation. It is high ly likely that a fast equilibrium is attained between the gauche and t he trans conformations in the liquid phase after 500 ms from the sudde n melting and that the crystal re-growth takes place solely via the al l-trans structure in the liquid phase.