Vibration-rotation alchemy in acetylene ((C2H2)-C-12), (X)over-tilde(1)Sigma g(+) at low vibrational excitation: from high resolution spectroscopy to fast intramolecular dynamics

The link between energy-resolved spectra and time-resolved dynamics is explored quantitatively for acetylene ((C2H2)-C-12), (X) over tilde (1)Sigma(+)(g) with up to 8600 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. Thievin, B. Rowe, and R. Georges, J. Chem. Phys. 131, 114301 (2009)]. Simulated intensity borrowing features in high resolution absorption spectra and predicted survival probabilities in intramolecular vibrational redistribution (IVR) are first investigated for the v(4)+v(5) and v(3) 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 phi(d), the IVR lifetime tau(IVR), and the recurrence time tau(rec). For the two bright states v(3)+2v(4) and 7v(4), the collisionless dynamics for thermally averaged rotational distributions at T = 27, 270 and 500 K were calculated from the available spectroscopic data. For the 7v(4) 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.