Density dependence of optical Kerr lens signals in neat N2O and CO2

Abstract

Optical Kerr lens spectroscopy has been employed to study the reorientation dynamics of N2O and CO2 at the reduced densities 0.8-2.0 and different temperatures in a newly constructed high pressure cell. The transient birefringence induced in the medium by an ultra-short (110 fs) non-resonant pump beam at 400 nm was monitored by a second, time-delayed non-resonant probe beam at 800 nm. The transient change of the probe beam diameter was detected in the far field using a small-area photodiode. Measurements employing parallel and perpendicular polarization allowed us to extract the nuclear and electronic components of the Kerr effect, where the latter one was by far weaker for both CO2 and NO. Accurate time constants for the reorientation dynamics of the CO2 and N2O molecules were extracted from the tail of the nuclear Kerr response. In the case of CO2 the time constants tau(reorientation) were between 2 10 and 280 fs and in good agreement with previous data from NMR and OHD-OKE experiments as well as MID simulations. Reorientation time constants for NO were in the range between 200 and 340 fs, and thus very similar to CO2. In the density range studied, increases with increasing viscosity and decreasing temperature, in agreement with Stokes-Einstein-Debye diffusive models. (c) 2006 Elsevier B.V. All rights reserved.