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Raman spectroscopy of nonrigid molecules in supersonic jets

AuthorsFernández Sánchez, José María
Issue Date3-Oct-2019
Citation1st Workshop on Nonrigid Molecules in Atmospherical and Astronomical Environments (2019)
AbstractNonrigid molecules often have low energy modes, which can be populated at room temperature and even at the temperatures of astrophysical environments like ¿hot¿ molecular clouds. Furthermore, these low frequency modes usually involve large amplitude motions, which depart markedly from the harmonic approximation, with splittings due to tunneling across the potential barriers separating the different stable conformations. Finally, the high density of states favors the coupling between them through resonances of any kind. Therefore, their spectra are much more complex and difficult to analyze than those of the ¿rigid¿ molecules. Raman spectroscopy has been useful in the past [1¿5] to locate many of these low frequency modes (and their associated ladder of energy levels) in nonrigid molecules for several reasons, among them: 1. in molecules with some symmetry, some of these modes are only Raman active 2. the first overtones of these modes are always totally symmetric, and thus Raman active 3. totally symmetric modes give rise to definite, polarized, Q branches in the Raman spectrum More recently [6], the combination of Raman spectroscopy with the cooling efficiency of supersonic jets posed a real breakthrough. In this contribution, we will recall the fundamentals of Raman spectroscopy in supersonic jets, and its current capabilities will be illustrated with some examples like ethane, dimethyl¿ether [7] and methylformate. [1] C. J. Wurrey, J. R. Durig, L. A. Carreira. ¿Gas Phase Raman Spectroscopy of Anharmonic Vibrations¿, in Vibrational Spectra and Structure, vol. 5, Chap. 4. J. R. Durig, ed. (Elsevier 1976). [2] D. A. C. Compton, S. Montero, W. F. Murphy. ¿Low¿frequency Raman spectrum and asymmetric potential function for internal rotation of gaseous n¿butane¿. J. Phys. Chem. 84, 3587 (1980). [3] R. Fantoni, K. Helvoort, W. Knippers, J. Reuss. ¿Direct observation of torsional levels in Raman spectra of C2H6¿. Chem. Phys. 110, 1 (1986). [4] J. M. Fernández¿Sánchez, A. G. Valdenebro, S. Montero. ¿The torsional Raman spectra of C2H6 and C2D6¿. J. Chem. Phys. 91, 3327 (1989). [5] R. Engeln, J. Reuss, D. Consalvo, et al. ¿Torsional motion of the CH3 groups of propane studied by Raman overtone spectroscopy¿. Chem. Phys. 144, 81 (1990). [6] S. Montero, B. Maté, G. Tejeda, J. M. Fernández, A. Ramos. ¿Raman studies of free jet expansion (Diagnostics and mapping)¿, in Atomic and Molecular Beams. The State of the Art 2000, R. Campargue, ed. (Springer, Berlin, 2001). [7] J. M. Fernández, G. Tejeda, M. Carvajal, M. L. Senent. ¿New spectral characterization of dimethyl ether isotopologues CH3OCH3 and 13CH3OCH3 in the THz region¿. Astrophys. J. Suppl. Ser. 241, 13 (2019).
Descriptionniversity of Huelva, October 3 - 4 2019
Appears in Collections:(CFMAC-IEM) Comunicaciones congresos
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