ANALYSIS OF OBSERVED SPLITTINGS IN THE ANTISYMMETRIC C-H STRETCHING BAND OF $C_{2}{H_{3}}^{+}$

1. M. W. Crofton, M.F. Jagod, B.D. Rehfuss and T. Oka, J. Chem. Phys 91, 5139 (1989). 2. M. Bogey, H. Bolvin, M. Cordonnier, C. Demuynck, J.L. Destombes, R. Escribano and P.C. Gómez, Can. J. Phys. 72, 967 (1995).Author Institution: Inst. Estructura de la Materia, CSIC, Serrano, 119-123, 28006 Madrid, Spain.; "Fac, de Ciencias, Univ. Complutense", 28040 Madrid, Spain.$Crofton et al^{1}$ measured the splitting of a number of vibration-rotation lines in the antisymmetric CH stretching band of $C_{2}{H_{3}}^{+}$. A few splittings were also observed in the pure rotational spectrum of this $ion^{2}$. This experimental evidence supports ab initio predictions for an internal-rotation motion of the three H atoms around the CC core. The scarce data from the rotational spectrum can be interpreted, with a reasonable approximation, using a theoretical model and a potential function with a barrier slightly higher than that predicted by the ab initio results. However, the splittings observed in the infrared spectrum have eluded so far any interpretation, including variations on the shape and the barrier of the potential function. We present here the analysis of the infrared splittings using several models in which different molecular and Hamiltonian parameters are refined