A QUANTUM DYNAMICAL STUDY OF CH OVERTONES IN FLUOROFORM .2. EIGENSTATE ANALYSIS OF THE V(CH)=1 AND V(CH)=2 REGIONS

In this series, the multiple time scales and mechanisms of intramolecu lar vibrational-energy redistribution (IVR) present in the CH overtone s of fluoroform is investigated. In part II, we analyze the ab initio vibrational spectrum and dynamics of the upsilon(CH)=1 and upsilon(CH) =2 regions, explicitly treating all vibrational degrees of freedom. A wave operator sorting algorithm is used to develop an efficient vibrat ional basis. Spectral transformation, by a filtered-lanczos method, is used to accelerate eigenstate analysis. The theoretical spectrum of t he fundamental is nontrivial, predicting a close triplet of lines (wid th <6 cm(-1)) centered at 3048.3 cm(-1) and a weak line 20 cm(-1) upfi eld, due to coupling with a small subsystem of background modes: nu(4) (+/-) + nu(5)(+/-) + nu(6)(+/-), nu(2)(+/-) + nu(4)(+/-) + nu(6)(+/-), nu(3) + (2) nu(5). Furthermore, these background states mix with one another and other nearby background states via resonances omega(5) app roximate to (omega(3) + omega(6)), omega(2) approximate to omega(5), a nd (omega(4) + omega(6)) approximate to (omega(3) + omega(5)). An effe ctive Hamiltonian is used to assess chromophore-background and backgro und-background coupling. In contrast, the first overtone exhibits no s trong background resonances, rather the background modes function as a weakly coupled reservoir. IVR time scales and eigenstate convergence, with respect to the active space, are presented. (C) 1997 American In stitute of Physics.