Rotation–Vibration Constants of Acetylene*

The study of the absorption spectrum previously reported has been extended to include the 1900- to 2200- and the 4400- to 6750-cm−1 regions. Rotational analysis provides 20 states from which the following constants are determined: α1 = 6.82, α2 = 6.30, α3 = 5.60, α4 = −1.30, α5 = −2.20 × 10−3 cm−1 and Be = 1.18240 cm−1. This value was used with Be values for C2HD and C2D2 to determine the bond length of re(C−H)=1.0603 and re(C≡C)=1.2034Å.A total of 46 states was available, from this and other work, to determine a set of vibrational constants. About one-half of the 23 constants have been determined with acceptable precision. The remaining constants are still in doubt due, primarily, to resonances.