l-Type Doubling in Three π—π Bands of HCN

l-type doubling constants have been determined for the 0112–0110, 0113–0110, and 0311–0110 bands of HCN. The results, in units of 10—3 cm—1, are: 011201130311q′7.717.5415.4q′′7.517.267.21The accuracy of the constants is ±5% for the 0113 and 0311 bands, and ±1% for the 0112 band. The q′—q″ values obtained for the 0113 and 0112 bands agree within experimental error with the prediction of our empirical equation which relates q to the vibrational quantum numbers.