15min:

DANIIL STOLYAROV, ELENA POLYAKOVA AND CURT WITTIG, Department of Chemistry, University of Southern California, Los Angeles, California 90089.

A mass spectrometric depletion measurement has been performed for the NO₂ molecule in its bound region as well as above its gas phase dissociation threshold. In the bound region (17700 - 18300 cm^-1) that is known to be vibronically chaotic transitions are broadened and blue-shifted relative to their gas-phase counterparts. The spectrum is fitted relatively well by setting all shifts and width equal to 7cm^-1. Modest dispersion of these values are consistent with quantum chaos in NO₂. Relaxation is dominated by interaction of NO₂ with its non-superfluid helium nearest neighbors.

In the region above the gas-phase dissociation threshold (25125 - 30000 cm^-1) the mass depletion spectrum reveals no fine structure. The fast relaxation due to the interaction with the superfluid helium environment prevents photodecomposition of the NO₂ molecule over the entire range we explored.