摘要:

Two theoretical approaches to the calculation of the highly excited vibrational states are reviewed. Particular emphasis is placed on the choice of coordinates, and the ramification this choice has on the quality of the ensuing calculations. The essential ingredients of variational calculations are highlighted via four illustrative calculations. The standard approach of using a product basis of harmonic oscillators based on a rectilinear normal mode framework is discussed using the work of Maessen and Wolfsberg. The improvements to this basis are presented within the context of the calculation of Romanowskiet al. in which a self-consistent-field basis is employed. Bond-angle coordinates and the advantages they provide are demonstrated. This discussion focuses on the efficient algorithms which Carter and Handy developed for evaluating eigenvalues and eigenvectors of tri- and tetra-atomic molecules. For yet larger amplitude motion, associated with ‘floppy’ molecules, the combination of Jacobi coordinates and the discrete variable representation are reviewed in the context of a study of the eigenstates of HCN/HNC by Bacic and Light. Perturbative approaches are also considered. In particular, the application of canonical Van Vleck perturbation theory in a superoperator framework using curvilinear coordinates is reviewed. This section draws chiefly from the work of Sibert, McCoy, and Fried and Ezra.

ISSN:0144-235X    

DOI:10.1080/01442359009353236

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This review focuses on the vibrational spectra of icy solids, in particular ice I, and the value of the spectra in monitoring point defect activity within the various hydrogen-bonded networks. After a brief review of the spectra of icy substances containing only H2O or D2O, an attempt is made to update both the spectroscopic data and the interpretation by emphasizing recent results for isotopically diluted/decoupled D2O in H2O ice I, amorphous ice and the clathrate hydrates. These data are informative of the magnitude of the intramolecular and intermolecular O-H oscillator coupling strengths, the strength of the Fermi interaction between v1and 2v2, the influence of symmetric hydrogen bonding on the directionality of the water-molecule bond-dipole-moment derivative, and, perhaps most importantly, the spatial extent of the collective vibrations in icy substances. The interpretation of the spectra retains, and expands, the assignment of Whalley (1977) based on the view that intermolecular coupling forces, caused by hydrogen bonding (v1) and the polarization field (v3), give rise to collective oscillations that dominate the appearance of the infrared and Raman stretching-mode band complexes.

ISSN:0144-235X    

DOI:10.1080/01442359009353237

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This review concentrates on a time-resolved infrared-ultraviolet double-resonance technique which has revealed many aspects of spectroscopic properties and energy-transfer processes involving the formaldehyde-d2molecule, D2CO. The experiments comprise sequential pulsed excitation of D2CO by CO2and dye lasers, with visible-fluorescence detection. The infrared Pump laser excites a transition in the v4, v6or (2v4—v4) vibrational band, which prepares D2CO in a specific rovibrational quantum state. This is followed by rovibronic excitation by a tunable Probe laser,viathe 401, 601or 4 1/2 vibronic band in the à ←-[Xtilde] electronic absorption system of D2CO. Detailed spectroscopic information is obtained by keeping the product of sample pressure and Pump-Probe delay as small as possible (typically below 10 ns Torr), approaching collision-free conditions. Additional information on a range of collision-induced state-to-state energy transfer processes is obtained by varying the number of collisions experienced by the D2CO molecule in the interval between the Pump and Probe pulses. The following kinetic and mechanistic applications are reviewed: J-changing rotational relaxation arising from long-range molecular interactions; mode-to-mode vibrational energy transfer, with particular emphasis on the role of rotational energy states and intramolecular perturbations; the way in which collision-induced molecular processes may be modified by selecting the rovibrational quantum state of the formaldehyde molecule and by varying its collision partner; and infrared multiple-photon excitation and laser photochemistry.

ISSN:0144-235X    

DOI:10.1080/01442359009353238

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor