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A calculated exhaustive set of vibrational state energies in 12 C 2 H 2 , 13 C 2 H 2 and 12 C 2 D 2 has been used to analyse the evolution of the integrated number of states with increasing vibrational energy N(E) up to 15 000 cm -1 , 12 000 cm -1 and 10 000 cm -1 in each isotopomer, respectively. The regular contribution to N(E) was modelled analytically and numerical parameters were fitted. The other expected contribution to N(E) , which is of oscillatory nature, was quantified and is discussed using energy- and time-dependent theories. Related periods of oscillation and temporal recurrences are interpreted consistently in terms of the constant of the motion N r = 5 v 1 +3 v 2 +5 v 3 + v 4 + v 5 and of an average vibrational quantum. More pragmatically, the vibrational dynamics appear to be dominated by the bending vibrations, i.e., by the slowest oscillators. [ABSTRACT FROM AUTHOR]

Intra- and interpolyad structures are investigated in the vibrational energy pattern of acetylene, using the spectroscopic Hamiltonian presented in previous papers in this series [see El Idrissi et al., J. Chem. Phys. 110, 2074 (1999)]. The existence of two constants of the motion is shown to generate very regular patterns in the manifold of vibrational energy levels. Distinct regular and oscillatory contributions are evidenced in the number of vibrational levels in the main polyads, which are fully reproduced using the generating function presented in Sadovskií and Zhilinskií [J. Chem. Phys. 103, 10520 (1995)]. Further developments of this approach are outlined. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The absorption spectrum of [sup 12] C[sub 2] H[sub 2] has been recorded by intracavity laser absorption spectroscopy (ICLAS) in the 10600-11500cm[sup -1] spectral region, where no absorption bands were previously reported. Fifteen bands starting from the vibrational ground state are observed and rotationally analysed. All corresponding excited vibrational levels were assigned using the polyad model, the so-called cluster model (El Idrissi, M.I., Liévin, J., Campargue, A., and Herman, M., 1999, J. chem. Phys. , 110, 2074) which allows vibrational energies, rotational B[sub V] constants and, to some respect, relative band intensities to be predicted. Additional data and constants are also provided in the range 7600-9200cm[sub -1] , whenever improving the literature results, from spectra recorded previously at ULB using Fourier transform spectroscopy. The assignment procedure in the range recorded by ICLAS is detailed, leading to a deeper understanding of vibration-rotation and intensity features of the absorption bands within the frame of the cluster model. [ABSTRACT FROM AUTHOR]