Self-focusing in SF6

It is shown by explicit calculation of the previously published quasicontinuum model that the molecular susceptibility rapidly approaches zero as higher excited states of the molecule become populated. Hence the overtones of the nu3-pumped mode are totally responsible for the self focusing effects in SF6. The nu3 ladder contribution to the susceptibility is calculated. The vibrational model is a classical triply degenerate anharmonic oscillator in the Cartesian basis with the anharmonicity parameters chosen to be consistent with the latest spectroscopic anlaysis of the 3nu3 overtone spectrum. The rotational structure is represented by a distribution of these oscillators where the distribution is chosen to correspond to the spectrum of the nu3 fundamental. Good agreement is found with the 300K self-focusing data of Nowak and Ham at CO2 P(28), P(20) and P(10) in SF6