TY - JOUR
T1 - Intramolecular vibrational relaxation in aromatic molecules. 2
T2 - An experimental and computational study of pyrrole and triazine near the IVR threshold
AU - Callegari, A.
AU - Pearman, R.
AU - Choi, S.
AU - Engels, P.
AU - Srivastava, H.
AU - Gruebele, M.
AU - Lehmann, K. K.
AU - Scoles, G.
N1 - Funding Information:
This work was supported by grants from the National Science Foundation (CHE-9986670 for M.G. and CHE-9703604 for K.L. and G.S.). M.G. was a Dreyfus Teacher-Scholar while this work was carried out.
PY - 2003/2/20
Y1 - 2003/2/20
N2 - The threshold region of vibrational energy redistribution (IVR) presents a great experimental and computational challenge for organic molecules with more than 10 degrees of freedom. The density of states ρtot is high and requires high resolution measurements over a wide range to cover all relevant timescales experimentally. Yet ρtot is sufficiently low that IVR quantities like the initial relaxation time τIVR or the number of participating states Neff are very sensitive to the coupling structure. To highlight the competing effects of molecular symmetry and mode localization on the accessible density of states, this work complements a study of benzene (Callegari, A., Merker, U., Engels, P., Srivastava, H. K., Lehmann, K. K., and Scoles, G., 2000, J. chem. Phys., 113, 10583) by measuring the CH overtone spectra of pyrrole (C4H4NH) and 1,2,3-triazine (C3N3H3) using eigenstate-resolved double-resonance spectroscopy. Large scale computations of IVR dynamics were undertaken, applying filter diagonalization to analytically fitted fourth-order ab initio force fields. With an overall adjustment to the anharmonicity of the potential, the modelled Neff and τIVR agree with the experimental quantities within a factor of 2 to 3, which is reasonable for a rate theory in the threshold regime. The models also correctly predict the experimentally observed trends of τIVR and Neff for the two molecules, and provide insight into the highly off-resonant coupling mechanism, which yields very sharp linewidths.
AB - The threshold region of vibrational energy redistribution (IVR) presents a great experimental and computational challenge for organic molecules with more than 10 degrees of freedom. The density of states ρtot is high and requires high resolution measurements over a wide range to cover all relevant timescales experimentally. Yet ρtot is sufficiently low that IVR quantities like the initial relaxation time τIVR or the number of participating states Neff are very sensitive to the coupling structure. To highlight the competing effects of molecular symmetry and mode localization on the accessible density of states, this work complements a study of benzene (Callegari, A., Merker, U., Engels, P., Srivastava, H. K., Lehmann, K. K., and Scoles, G., 2000, J. chem. Phys., 113, 10583) by measuring the CH overtone spectra of pyrrole (C4H4NH) and 1,2,3-triazine (C3N3H3) using eigenstate-resolved double-resonance spectroscopy. Large scale computations of IVR dynamics were undertaken, applying filter diagonalization to analytically fitted fourth-order ab initio force fields. With an overall adjustment to the anharmonicity of the potential, the modelled Neff and τIVR agree with the experimental quantities within a factor of 2 to 3, which is reasonable for a rate theory in the threshold regime. The models also correctly predict the experimentally observed trends of τIVR and Neff for the two molecules, and provide insight into the highly off-resonant coupling mechanism, which yields very sharp linewidths.
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U2 - 10.1080/0026897021000014910
DO - 10.1080/0026897021000014910
M3 - Article
AN - SCOPUS:1542348250
SN - 0026-8976
VL - 101
SP - 551
EP - 568
JO - Molecular Physics
JF - Molecular Physics
IS - 4-5
ER -