COMPUTATIONAL TOOLS FOR HIGH-RESOLUTION SPECTROSCOPY

Attila  G.  CSÁSZÁR  
Laboratory of Molecular Spectroscopy
Institute of Chemistry, Eötvös University
H-1117 Budapest, Pázmány Péter sétány 1/A, Hungary
Tel. (+361) 372 2929,  Fax (+361) 372 2592

Email:  csaszar@chem.elte.hu
http://theop11.chem.elte.hu/

While many scientific and engineering applications, including star and planetary formation models, combustion, and the understanding of the greenhouse effect, need the related information, understanding the rotational-vibrational spectra of even small molecules as completely as possible is an almost formidable task [1,2]. Neither experiments nor first-principle computations can determine this information. It seems to us that the most practical approach to overcome most of the associated difficulties is through an active database approach [1-3] built both on experimental results and on the utilization of computational tools and information technology. This way one can take advantage of the strengths of the two main sources of spectroscopic information. Variational nuclear motion quantum computations (e.g., using the protocols and packages DEWE [4] or GENIUSH [5]) can yield all the possible energy levels, at least in principle, with various assignment possibilities, and thus all the possible labeled transitions, though with limited accuracy deteriorating as the level of rovibrational excitation increases [1-6]. Experimental transitions, and the energy levels obtained through an appropriate inversion procedure (like MARVEL [3]), have a much higher accuracy but are limited in number even in the spectroscopically accessible regions. The strength and weaknesses of all the computational procedures involved are described during the talk.

[1]	A. G. Császár, G. Czakó, T. Furtenbacher, and E. Mátyus, An Active Database Approach to Complete Rotational-Vibrational Spectra of Small Molecules, Ann. Rep. Comp. Chem. 3, 155-176 (2007).
[2]	J. Tennyson, P. F. Bernath, L. R. Brown, A. Campargue, M. R. Carleer, A. G. Császár, R. R. Gamache, J. T. Hodges, A. Jenouvrier, O. V. Naumenko, O. L. Polyansky, L. S. Rothman, R. A. Toth, A. C. Vandaele, N. F. Zobov, L. Daumont, A. Z. Fazliev, T. Furtenbacher, I. F. Gordon, S. N. Mikhailenko, and S. V. Shirin, IUPAC Critical Evaluation of the Rotational-Vibrational Spectra of Water Vapor. Part I. Energy Levels and Transition Wavenumbers for H217O and H218O, J. Quant. Spectr. Rad. Transfer 110, 573-596 (2009).
[3]	T. Furtenbacher, A. G. Császár, and J. Tennyson, MARVEL: Measured Active Rotational-Vibrational Energy Levels, J. Mol. Spectry. 245, 115-125 (2007).
[4]	(a) E. Mátyus, G. Czakó, B. T. Sutcliffe, and A. G. Császár, Variational Vibrational Calculations with Arbitrary Potentials Using the Eckart-Watson Hamiltonians and the Discrete Variable Representation, J. Chem. Phys. 127, 084102 (2007). (b) E. Mátyus, J. Simunek, and A. G. Császár, On Variational Computation of a Large Number of Vibrational Energy Levels and Wave Functions for Medium-Sized Molecules, J. Chem. Phys. 131, 074106 (2009).
[5] E. Mátyus, G. Czakó, and A. G. Császár, Toward Black-Box-Type Full- and Reduced-Dimensional Variational (Ro)vibrational Computations , J. Chem. Phys. 130, 134112 (2009).
[6]	O. L. Polyansky, A. G. Császár, S. V. Shirin, N. F. Zobov, P. Barletta, J. Tennyson, D. W. Schwenke, and P. J. Knowles, High-Accuracy Ab Initio Rotation-Vibration Transitions for Water, Science 299, 539-542 (2003).