Effects of IR laser frequency on C2H5OH conversion in multiphoton excitation

It is unlikely that unimolecular reactions selective as regards excited modes will occur on IR multiphoton excitation for pulse lengths tau p of 10-7-1078 sec because there is rapid intramolecular energy exchange between modes (tau ≤ 10711 sec), but even with such tau p, one can alter the reaction trends in certain cases by using laser frequencies corresponding to various vibrational modes. The effective absorption cross sections σ/sub ef/ for the various exciting frequencies are unequal. The differences in these cross sections lead to differences in energy density as the frequency is varied, so there are changes in the conditions for competition between the low-energy and high-energy channels, whose relative importance in the reaction alters. It is more likely that the molecules will be excited above the threshold E2 for the low-energy reaction to the levels necessary for the high-energy reaction at a frequency that corresponds to the larger σ/sub ef/. The differences in the absorption cross sections for frequencies corresponding to the excitation of various vibrational modes can lead to changes in trend in multichannel reactions with frequency