A Model to Describe Quasicontinuum Effects in Dissociation of Polyatomic Molecules

Abstract

A widely used model for laser-induced dissociation of polyatomic molecules assumes that the vibrational spectrum of the molecule can be divided into three regions according to the value of the level density (see Ref. 1). The first region consists of the harmonic part of the particular vibrational mode which is resonant with the laser field. After a few photons have been absorbed the anharmonicity barrier stops the excitation in this mode but the process can continue due to the coupling to the levels of other vibrational modes. In polyatomic molecules the density of these levels is so high that they are said to form a quasicontinuum (QC). In this second region the process continues more easily without strict energy matching requirements characteristic to the initial stage of the excitation. The third region is the true continuum where the molecule dissociates.