Intramolecular vibrational redistribution in Ne-Br2:: The signature of intermediate resonances in the excitation spectrum

Quantum-mechanical simulations of the Ne-Br-2(B,v(')) excitation spectra produced after vibrational predissociation in the v(')=20-35 range are reported. The aim is to investigate the signature in the excitation spectra of intermediate resonances lying in the lower v < v(') vibrational manifolds in order to elucidate their role in the intramolecular vibrational redistribution (IVR) mechanisms in Ne-Br-2. By increasing v('), the energy position of the Ne-Br-2(B,v(')) initial state probes the whole range of the spectrum of v(')-1 intermediate resonances, from the continuum resonance states above the Ne+Br-2(B,v(')-1) dissociation threshold to the resonances below that threshold. In general, the results show that the Ne-Br-2(B,v(')) initial state couples more strongly to the energetically nearby v(')-1 resonances, although coupling to farther away resonances also occurs with appreciable intensity. The excitation spectra reveal a strong overlapping between spectral features, indicating that the intermediate resonances are coupled and interfere between themselves. This coupling generates an interconnected network of intermediate resonances, through which an efficient flow of the initial population leading to IVR takes place. It is found that the density of continuum resonances reaches a maximum in the region just above the Ne+Br-2(B,v(')-1) threshold, and it decreases gradually with increasing energy above this threshold, as suggested in a previous work. An upper energy limit for the spectrum of v(')-1 continuum resonances has been estimated to be about 23-29 cm(-1) above the v(')-1 dissociation threshold. The excitation spectra reflect that coupling of the initial state with intermediate resonances lying below the Ne+Br-2(B,v(')-1) threshold can occur in a remarkably wide range of the resonance spectrum. (c) 2007 American Institute of Physics.