Vibration-rotation bands of acetylene and the molecular dimensions

Abstract

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, α2, α3 and (α4 + α5) for acetylene are in line with the corresponding values for the deuterated derivatives, and using Bo = 1·1766 lead to Be + 1·1817. If bond lengths re(CH) = 1·0585, re(CC) = l·2047 Å are assumed, the results for all three isotopic molecules are mutually consistent. Values have also been obtained for the l-doubling coefficients, q4 and q5.