Vibration-rotation alchemy in acetylene (12C2H2), at low vibrational excitation: From high resolution spectroscopy to fast intramolecular dynamics

David Perry (1) , Anthony Miller (2) , Badr Amyay (3) , André Fayt (4) , Michel Herman (3)

1 Chemistry
2 University of Akron
3 Service de Chimie Quantique et Photophysique
4 UCL - Université Catholique de Louvain = Catholic University of Louvain

The link between energy-resolved spectra and time-resolved dynamics is explored quantitatively for acetylene (12C2H2), with up to 8,600 cm-1 of vibrational energy This comparison is based on the extensive and reliable knowledge of the vibration-rotation energy levels and on the model Hamiltonian used to fit them to high precision (B. Amyay, S. Robert, M. Herman, A. Fayt, B. Raghavendra, A. Moudens, J. Thiévin, B. Rowe, and R. Georges, J. Chem. Phys. 131 (2009) 114301-114314). Simulated intensity borrowing features in high resolution absorption spectra and predicted survival probabilities in intramolecular vibrational redistribution (IVR) are first investigated for the n4+n5 and n3 bright states, for J = 2, 30 and 100. The dependence of the results on the rotational quantum number and on the choice of vibrational bright state reflects the interplay of three kinds of off-diagonal resonances: anharmonic, rotational l-type, and Coriolis. The dynamical quantities used to characterize the calculated time-dependent dynamics are the dilution factor Fd, the IVR lifetime TIVR, and the recurrence time Trec. For the two bright states n3+2n4 and 7n4, the collisionless dynamics for thermally averaged rotational distributions at T = 27, 270 and 500 K were calculated from the available spectroscopic data. For the 7n4 bright state, an apparent irreversible decay of is found. In all cases, the model Hamiltonian allows a detailed calculation of the energy flow among all of the coupled zeroth-order vibration-rotation states.

Mots clés: Physical Sciences

David Perry, Anthony Miller, Badr Amyay, André Fayt, Michel Herman. Vibration-rotation alchemy in acetylene (12C2H2), at low vibrational excitation: From high resolution spectroscopy to fast intramolecular dynamics. Molecular Physics, 2010, 108 (07-09), pp.1115-1132. ⟨10.1080/00268971003660874⟩. ⟨hal-00596282⟩