8 research outputs found
The first overtone of CH-stretchings in Polymethylene chains: a conformationally dependent spectrum
No full textTHE USE OF FOURIER TRANSFORM IN INTERPRETING VIBRATIONAL. SPECTRA.
No full text C. Jaff\'{e}, and P. Brumer, J. Chem. Phys., 73, 5646 (1980); E. L. Sibert III, W.P. Reinhardt, and J. T. Hynes, S. Che., Ptys., 77, 3583 (1982) G. Longhi, S. Abbate, C. Zagano, G. Botto, and L. Ricard-Lespade. Theor. Chim. Acta, 82, 321 (1992) D.W. Noid, M.L., Koszykowaky, and R.A. Marcus, J. Chem. Phys., 67, 404 (1977)Author Institution: Dipartimento di Chimica, Universit\""{a} della Basilicata.; Dipartimento di Matematica, Universit\'{a} dl Milano; Laboratoire de Spectroscopie Moleculaire, Universit\'{e} de Bordeaux IThe investigation of molecular vibrations through non-linear classical mechanics has achieved considerable success in accounting for the transition from the normal mode to the local mode regime(1). We have recently proved the existence of some peculiar type of modes, which differ from both local and normal modes, in a system of two coupled Morse oscillators (2). In this work we analyze the Fourier transform of some vibrational autocorrelation functions derived from numerical integration of the classical equations of motion(3). We applied these theoretical calculations to gain insight into the quasiperiodic vibrational motions of -type oscillators. Eventually we intend to use these results to further understand observed overtone absorption spectra of molecules containing methylenic groups
Analysis of the transition from Normal Modes to Local Modes in a system of two harmonically coupled Morse oscillators
No full textThe system consisting of two Morse oscillators coupled via either a
potential or a kinetic quadratic term is considered. The corresponding classical
equations of motion have been numerically integrated and the initial conditions
have been systematically analyzed in the regime of low total excitation energy of
the system. Particular attention was paid to the full characterization of an
intermediate type of motion, herein called transition mode, which appears at
total energy values in between those typical of normal modes and those where
local and normal modes coexist. A previously proposed perturbative approach
(Jaffé C, Brumer P (1980) J Chem Phys 73:5646) is reanalyzed and compared
with the results of numerical experiments, with the purpose of lending further
support to the existence of transition modes
HIGH VIBRATIONAL STATE ENERGY REDISTRIBUTION IN PARTIALLY DEUTERATED CYCLOPENTENES
No full text S. Rodin-Bercion, D. Cavagnat, L. Lespade and P. Maraval, J. Phys. Chem., 99, 3005 (1995) L. Lespade, S. Rodin-Bercion and D. Cavagnat, J. Phys. Chem., 101, 2568 (1997)Author Institution: LPCM, Universit\'{e} Bordeaux IExperimental investigations of high vibrational states in medium-size molecules show clear evidence of large intramolecular redistribution of the vibrational energy (IVR). In particular, the CH bond stretching vibration energy rapidly relaxes in combination states involving deformations of the angles adjacent to the initially excited CH . In this contribution, the overtone spectra ( to 6) of cyclopentene and cyclopentene are analyzed with a model formulated in curvilinear internal coordinates including also the coupling between the ring-puckering motion and the vibrations. In the dihydrogenated compound, the analysis of the spectra indicates a progressive localization of the CH stretching vibrations with increasing energy. At high energy (from to 6), the spectra of the two compounds evidence different IVR for CHD or groups
HIGH VIBRATIONAL STATES OF 1,2,3,4,4,5,5-d7 and 3,3,4,4-d4 CYCLOPENTENES.
No full text D CAVAGNAT. S BANISAED-VAHEDIE. L LESPADE, S RODIN. J.Chem.Soc.Faraday Trans. 88(13), 1845 (1992).Author Institution: Laboratoire de Spectroscopie Moleculaire et Cristalline, URA 124. 351 ers de la Lib\'{e}ration; Laboratoire de Spectroscopie Moleculaire et Cristalline, Universit\`{a} della Basilicata.The ring-puckering motion of cyclopentene is studied through the CH bond stretching overtones to 6) of the monohydrogenated and dihydrogenated . At high energies, the potential of the large amplitude motion may be divided into two parts: one part, which corresponds to the potential of the motion in its ground state and another part, due to the vibrational dissymetry of the CH bond stretchings. Because of this vibrational part. the potential wells, corresponding to the two axial and equatorial positions of the CH bonds, become deeper and deeper with increasing molecular energy. Thus, there is a relative ``localization'' of the high vibrational energy in the two potential wells, which is counterbalanced by its rapid redistribution in combination states through Fermi resonance couplings. The two phenomena are qualitatively modelled
CLASSICAL DYNAMICS OF LOCAL CH-STRETCHINGS OF AN ALMOST FREELY ROTATING METHYL GROUP
No full text(1)D. Cavagnat and L. Lespade, J. Chem. Phys., 106, 7946 (1997) (2)C. Zhu, H.G. Kjacrgaard, and B.R. Henry, J. Chem. Phys., 107, 691 (1997)Author Institution: Dipartimento di Scienze Biomediche e Biotecnologi, Universit\`{a} di BresciaCavagnat and Lespade have extensively examined the CH-stretching fundamental and overtone spectra of molecules containing an almost freely rotating -group: Nitromethane. Toluene, etc. They were able to interprete the spectroscopic features by a model based on the assumption of moderate variations of the rotational potential with the stretching quantum number. Their approach was also tried on the same or similar molecules containing undeuterated methyl We have examined a classical model for almost freely rotating and -groups, allowing for just kinetic coupling between the CH-stretching and the methyl hindered rotation, with three different values for the rotation barrier applicable to the cases presented in refs. (1) and (2). While for just two types of classical regular trajectories are found at all overtone orders, namely those exhibiting either a torsion or a rotation in the methyl, for a third type of trajectories appears at high overtone order, showing a 1:6 (or 1:12) resonance between the CH-stretching and the hindered rotation frequencies and a secondary 1:1 (or 1:2) resonance which is particularly evident in the momenta. The consequences of this fact in the semiclassical quantization scheme for the construction of the spectra will be discussed
MOLECULAR BEAM INFRARED SPECTRUM OF THE FIRST C-H STRETCHING OVERTONE REGION OF NITROMETHANE
No full textPermanent address of M. and L. Halonen: Laboratory of Physical Chemistry, P.O. Box 55 (A.I. Virtasen aukio 1). FIN-00014 University of Helsinki, Finland D.Cavagnat, L. Lespade, and C. Lapouge, Ber. Bunsenges Phys. Chem. 99, 544 (1995)Author Institution: Department of Chemistry, Princeton UniversityThe first C-H stretching overtone region of nitromethane has been measured using a bolometer detected molecular beam machine with a resonance cavity. Nitromethane is an almost free rotor with a very low torsional barrier in the ground state. The purpose of this study is to find out whether the low 6-fold barrier of the ground state will turn to a much higher 2-fold barrier in the first stretching vibrational overtone of nitromethane with 2 quanta of stretching vibrational This might happen, if the vibrational energy would stay localised in one bond long enough compared with the period of internal rotation. The spectrum of nitromethane has been measured in the wavenumber region with a resolution of 5MHz. As the rotational temperature is very low, only levels with the internal rotation quantum number m=0 and m=1 should be significantly populated. The spectrum has been assigned using ground state combination differences. Using a rigid rotor program the band center and the rotational constants have been obtained for the m=0 state. The analysis of the m=1 state is in progress
ANALYSIS OF THE TRANSITION FROM NORMAL MODES TO LOCAL MODES
No full textAuthor Institution: Dipartimento di Chimica Fisica, Universit{\'a} di Palermo; Dipartimento di Fisica, Universit\'{a} di Milano; Laboratoire de Spectroscopic Moleculaire et Cristalline, Universtit{\'e} de Bordeaux 1By numerical integration of the classical equations of motion for a system of two coupled anharmonic oscillators, one can define the vibrational motions as follows: normal modes, for which energy is exchanged between the two oscillators and their phase difference is almost constant; local modes, for which the energy of one oscillator is always greater than the other’s and their phases are independent (1). We found a third type of modes, that we called transition modes, which show phase relation between the two oscillators and yet no energy exchange. They appear at total energy values intermediate between those typical for normal modes and for local modes. We tested our finding by two perturbative approaches, based on local modes and normal modes respectively. In this note we will point out the parameters favoring a wide extent of transition modes, in order to look for a spectroscopic signature of such modes. E. L. Sibert III, W. P. Reinhardt, J. T. Hynes, J. Chem. Phys., 77, 3583(1982
