Ring Puckering and CH Stretching Spectra. 2. High Vibrational States of Gaseous Monohydrogenated Cyclopentene-3-h1

Abstract

The excited vibrational states of gaseous cyclopentene 3-HCsD7 have been measured up to Av = 7. The second overtone presents essentially two main absorptions corresponding to two distinct conformers. The higher overtones are much perturbed by Fermi resonances with low-energy modes. The contribution of two types of couplings to the ring-puckering motion and to isoenergetic states involving low-energy modes are analyzed and modeled. Through the reconstruction of the spectra, the predominant pathways of the intramolecular vibrational redistribution of the energy (IVR) are discussed.

Ring Puckering and CH Stretching Spectra. 3. High Vibrational States of Gaseous Monohydrogenated Cyclopentene-4-h1

“…More generally, there is a discrepancy between the values of almost all the effective parameters in the two conformations contrary to what observed for Cy3H compound. 26 In the equatorial position, the anharmonic parameters involving both bending and wagging vibrations are of the same order of magnitude as those determined for Cy3H compound. On the contrary, these parameters are significantly larger in the axial conformation.…”

“…26 They correspond to the first and second derivatives of g θ i θ i 0 in the displacement coordinates about the equilibrium configuration and the corresponding potential energy terms.…”

“…In particular, the very short time intramolecular vibrational redistribution (IVR) dynamics of CH overtones has been shown to be largely uncorrelated to the total state density 7,8 and to be governed by strong couplings with specific states: bending states in small molecules 9-24 or bending and wagging modes in hydrocarbons. 25,26 In flexible molecules, the CH stretching vibrations are also modified by the large-amplitude motion. When the movement is slow enougth as in cyclohexene, there is no competition between the two phenomena, and the vibrational energy dynamics is essentially governed by the strong Fermi resonance couplings.…”

Theoretical and Spectroscopic Study of Gaseous Monohydrogenated Toluene and 4-Methylpyridine

“…These types of motions are generally coupled with vibrational motions, particularly with the CH stretching vibrations. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] This coupling induces a conformational dependence of the CH vibrators, which become nonequivalent during the largeamplitude motion, and leads to complex features observed in the fundamental Raman and infrared spectra. [1][2][3][4][5][6][8][9][10] The internal rotation of the methyl group in toluene and γ-picoline in the gas phase is a quasifree motion, with barriers of 4.9 and 4.75 cm -1 for toluene 15 and γ-picoline, 16 respectively as determined by microwave.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] This coupling induces a conformational dependence of the CH vibrators, which become nonequivalent during the largeamplitude motion, and leads to complex features observed in the fundamental Raman and infrared spectra. [1][2][3][4][5][6][8][9][10] The internal rotation of the methyl group in toluene and γ-picoline in the gas phase is a quasifree motion, with barriers of 4.9 and 4.75 cm -1 for toluene 15 and γ-picoline, 16 respectively as determined by microwave. Analysis of vibrationally excited CH stretching spectra of toluene 11,13 and some of its fluoro derivatives 12,14 (from ∆v ) 3 to 7) shows that the complex structure is conserved in the excited states.…”