Vibration-rotation bands of acetylene and the molecular dimensions

Abstract

In view of recent inconsistencies in the relation between the bond lengths and rotational constants in the isotopic acetylenes, some vibration-rotation bands of acetylene have been re-measured, and the results have been analyzed together with earlier work on this molecule. The α values for each of the molecular vibrations have been re-determined, taking into account possible vibrational perturbations and also anomalous changes in the centrifugal stretching constant D of the different vibrational levels. The new values of α , 1 , α 2 , α 3 and ( α 4 + α 5 ) for acetylene are in line with the corresponding values for the deuterated derivatives, and using B o = 1·1766 lead to B e + 1·1817. If bond lengths r e (CH) = 1·058 5 , r e (CC) = l·204 7 Å are assumed, the results for all three isotopic molecules are mutually consistent. Values have also been obtained for the l -doubling coefficients, q 4 and q 5 .