INTRAMOLECULAR VIBRATIONAL ENERGY REDISTRIBUTION IN ISOLATED NAPHTHALENE

[摘要] The rate and extent of intramolecular vibrational redistribution (IVR) following optical excitation in an isolated naphthalene molecule has been measured using the technique of supersonic free-jet spectroscopy. Naphthalene, exicted to its first (('1)B(,3u)) or second (('1)B(,2u)) excited singlet state is found to undergo a rapid vibrational redistribution which is quite global in nature.The rate of the IVR process is measured by observation of the fluorescence excitation linewidths as a function of vibrational energy (E(,v)). A smooth, monotonic increase in the vibronic linewidths as vibrational energy is increased is observed, corresponding to redistribution rates ranging from 9 x 10('10) sec('-1) at E(,v) = 3068 cm('-1) to 7 x 10('11) sec('-1) at E(,v) = 5200 cm('-1).The extent of the redistribution is monitored via single vibronic level fluorescence spectra of naphthalene taken in a free-jet. At low vibrational excitation the fluorescence spectra display sharp, well resolved features, indicating that little redistribution has occurred on the time-scale of the fluorescence (nsec). However, at energies above E(,v) = 2122 cm('-1) the spectra become diffuse. Computor modeling of these spectra shows that many zero-order levels must be involved in the redistribution process, at least all of the quasi-resonant levels of the same symmetry as the originally pumped level. Therefore, even at moderate vibrational energies, an isolated molecule the size of naphthalene undergoes a rapid flow of vibrational energy among much of the energetically available vibrational phase space, following optical excitation.

[发布机构] Rice University

[效力级别] chemistry