Eigenstate resolved infrared/infrared double resonance spectroscopy of the 3ν1 overtone band of 1propyne: Intramolecular vibrational energy redistribution into a Corioliscoupled bath SubDoppler, infrared laser spectroscopy of the propyne 2ν1 band: Evidence of zaxis Coriolis dominated intramolecular state mixing in the acetylenic CH stretch overtone Spectroscopy and nonradiative relaxtion of propynal J. Chem. Phys. 77, 697 (1982); 10.1063/1.443884Electronimpact spectroscopy of the alkynes: A comparison of propyne and 1butyne with acetyleneThe vibrational overtone spectra of the acetylenic and methyl C-H stretches ofpropyne were obtained for the v = 1 to v = 6 and v = 1 to v = 7 levels, respectively. Propyne-dl was also studied and the methyl C-H stretching overtones were measured from v = 1 to the v = 7 level.The C-D stretch was observed only in the fundamental and first overtone regions. Lower level overtones were obtained by standard infrared techniques, while higher absorptions ( > 12000 cm -I) were obtained by intracavity dye laser photoacoustic spectroscopy. The C-H stretches in both molecules were analyzed in terms of the local-mode model, and harmonic frequencies (lU j ) and anharmonicities (Xu) were calculated. In propyne these values were (acetylenic C-H stretch) lUI = 3384 ± 5 cm -I and X l1 = -50 ± 1 cm -I and (methyl C-H stretch) lU m = 3037 ± 5 cm -I and Xmm = -65 ± 2 cm -I. In propyne-d I the methyl C-H stretch parameters were lU m = 3034 ± 5 cm -,I and X mm = -64 ± 2 cm -I. For propyne, a hot band (V9 -+ V9 + VV I ) accompanying the acetylenic C-H stretch was observed for v = 1-6 and the anharmonic interaction constant (X 19 = -23 ± 7 cm-I ) was calculated. A crossover from normal-to local-mode behavior has been observed for the methyl C-H stretches in propyne and propyne-d I at the v = 3 and 4 levels. Below v = 3 the symmetric and antisymmetric methyl C-H stretches are designated by the usual normal-mode notation (V2 and V6 in propyne; VI and V6 in propyne-dl), while for v>3 the single observed band is designated as a "methyl" C-H stretch, VV m • Peak absorption cross sections have been measured for aV I = 1-5, aV m = 3-5, aV 2 = 1 and 2, and the parallel component of2v6 in propyne, and for aV2 = 1 and 2, aV I = 1 and 2, aV m = 3 and 4, and the parallel component of2v 6 in propyne-dl. During the course of this work the spectral constants of 3,3,3-trifluoropropyne were redetermined. The harmonic frequency lUI is 3376 ± 6 cm -\ the anharmonicity X l1 is -49 ± 1 cm -I, and the anharmonic interaction constant X 17 is -17 ± 6 cm -I.
A study has been made of the vibrational energy flow mechanisms and time scales pertaining to the overtone stretch excitations of methyl and acetylenic CH stretches in propyne. Classical trajectories are used to interpret the experimental data for the overtone linewidths, as well as to analyze the role that individual modes play in determining energy flow. The full anharmonic potential surface for these calculations, including all modes, has been developed from spectroscopic and structural information, including the linewidth data. The principal results are: (1) The trajectory calculations show a localization transition, corresponding to a switch over from normal-mode behavior for CH3 excitations up to v≅3 to a local-mode CH excitation within the CH3 moiety for excitations of v≳6, with transition behavior for v=4,5. (2) The acetylenic CH shows local-mode behavior from v=1. Extremely long lifetimes are found for the excitations of this mode, and the trajectories indicate that the experimental width is predominantly rotational. (3) The rocking and deformation modes are dominant receiving modes in the relaxation of the methyl stretch. (4) A shorter lifetime is calculated for the v=6 vs the v=5 or v=7 overtones of the methyl C–H stretch. Experimental results are qualitatively consistent with this prediction. The origin of this shorter lifetime is a band of resonances between the stretch excitation and combinations of rocking, deformation, and pseudorotation modes. (5) CH3 internal rotation figures importantly in the relaxation of some levels (v=5, 8 of CH3) where it ‘‘closes the energy gap’’ for achieving resonant energy transfer. (6) For v=8 of the methyl CH, some direct energy transfer to both C–C≡C stretching modes is seen. The switching on of the stretches as receiving modes is a consequence of sufficiently strong interactions between the excited H and the C–C≡C chain, which take place at these high vibrational energies. (7) Evidence is found for long distance ‘‘through-space’’ energy transfer due to long-range dipole–dipole forces. This transfer occurs from the acetylenic to the methyl CH stretches. This result is illustrated for the v=2 excitation of the acetylenichydrogen, and constitutes a direct demonstration of intramolecular long-distance, through-space v–v energy transfer. These results demonstrate the potential importance of large amplitude modes such as rocking and deformation as initial receiving modes for vibrational energy from excited CH overtones. On the time scale probed here (∼1 ps), despite the availability of many degrees of freedom, the transfer process is dominated by specific energy transfer channels and by the specific behavior of individual modes, rather than by statistical considerations, which will certainly prevail on longer time scales.
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