SITE-RESOLVED VIBRONIC SPECTRA OF MATRIX-ISOLATED NBR - COMPARISON WITH MODEL-CALCULATIONS

The b 1-SIGMA+ <-> X 3-SIGMA-, a 1-DELTA --> X 3-SIGMA-, and b 1-SIGMA+ --> a 1-DELTA transitions of NBr in multiple trapping sites of an argon matrix have been characterized by the method of laser-induced fluorescence. Selective excitation yielded specific T(e)-, omega(e)-, and omega(e)x(e)-data for six trapping sites, only three of which were found to be unaffected by impurities. These were assigned to two nearly degenerate double substitutional (DS) trapping sites which can be removed by high-temperature annealing, and a single substitutional (SS) trapping site. The assignments are based on results of a site-sensitive modeling study (see preceding paper), which predicts that SS sites are thermodynamically more stable. An annealing mechanism, which assumes T-dependent dissociation into SS sites and mobile vacancies as rate controlling in the removal of DS sites, obtains quantitative support from model calculations.