Vibration-rotation bands and rotational constants of dideuteroacetylene

Nine vibrational absorption bands of dideutero-acetylene have been examined with very high resolving power. The rotational constants have been determined for the vibrational levels concerned, and the coefficients αi have been determined with more convincing accuracy than previously. In some of the bands the Q branches have been resolved, so that the l-doubling coefficients qi could be derived, and details could be established about the doublet components in some II levels. The results emphasize the need of high resolution if the vibrational assignments are to be unambiguous, and if reliable values of the rotational constants are to be derived. A value of Be has been obtained, and the vibrational anharmonicity coefficients have been considered briefly. Estimates of the centrifugal stretching constants Di in different vibrational states have been made, and one anomalous case has been found.