Two-frequency IR laser orientation of polar molecules. Numerical simulations for HCN

Using ab initio nuclear-coordinate-dependent dipole moments and polarizabilities, we study the orientation dynamics of HCN, by numerically solving the time-dependent Schrodinger equation, in the presence of a superposition of intense, linearly-polarized infrared laser pulses of frequency omega and 2 omega. We show that polarizability acts in concert with permanent dipole moments to orient polar molecules, as opposed to alignment which occurs alone with a single laser frequency or one moment only (permanent or induced). Optimal orientation occurs for the field configuration E(t)= E-0(t)(cos omega t + 0.5 cos2 omega t), where 2 omega is resonant with a 0 --> 1 vibrational transition and E-0(t) is a picosecond pulse. (C) 1999 Elsevier Science B.V. All rights reserved.