Dynamics of Single- and Multi-photon Ionisation Processes in Molecules

Single-photon ionisation and resonant multiphoton ionisation studies, which can now be carried out using synchrotron radiation and pulsed dye lasers respectively, are providing important dynamical information on molecular photoionisation. In this paper we discuss some results of our recent studies of several, single- and multi-photon ionisation processes in molecules. The results will be taken from our studies of (i) single-photon ionisation of linear molecules with emphasis on the role of shape and autoionising resonances on these cross· sections, (ii) photoionisation from oriented NiCO as a simple but realistic model of photoemission in adsorbate-substrate systems, and (iii) resonant multiphoton ionisation of H_2

Quantum and Semiclassical Calculations of Cold Atom Collisions in Light Fields

We derive and apply an optical Bloch equation (OBE) model for describing collisions of ground and excited laser cooled alkali atoms in the presence of near-resonant light. Typically these collisions lead to loss of atoms from traps. We compare the results obtained with a quantum mechanical complex potential treatment, semiclassical Landau-Zener models with decay, and a quantum time-dependent Monte-Carlo wave packet (MCWP) calculation. We formulate the OBE method in both adiabatic and diabatic representations. We calculate the laser intensity dependence of collision probabilities and find that the adiabatic OBE results agree quantitatively with those of the MCWP calculation, and qualitatively with the semiclassical Landau-Zener model with delayed decay, but that the complex potential method or the traditional Landau-Zener model fail in the saturation limit.Comment: 21 pages, RevTex, 7 eps figures embedded using psfig, see also http://www.physics.helsinki.fi/~kasuomin