Abstract
The rotational spectrum of the V10=2 vibrational state of propyne was investigated in the 17–70 GHz region with a total of 18 lines measured. Rotational constants for the V10=2 state have been derived. The rotational constants for the V10=2, V10=1, and ground vibrational states have been compared and the constants of anharmonicity describing the change of B with the level of excitation of the V10 vibrational mode have been derived. The constants derived in this manner are quite different from those calculated by Meyer and Sergent‐Rozey based on infrared data. An explanation for this discrepancy is given.