THE BENDING ENERGY-LEVELS OF C2H2

Absorption spectra of C2H2 have been recorded between 50 and 1450 cm-1, with a resolution always better than 0.005 cm-1, using two different Fourier transform spectrometers. Analysis of the data provided two sets of results. First, the bending levels with Σt Vt(t = 4, 5) ≤ 2 were characterized by a coherent set of 34 parameters derived from the simultaneous analysis of 15 bands, performed using a matrix Hamiltonian. The following main parameters were obtained (in cm-1): ω40 = 608.985196(14), ω50 = 729.157564(10); B0 = 1.17664632(18), α4 = -1.353535(86) × 10-3, α5 = -2.232075(40) × 10-3; q40 = 5.24858(12) × 10-3, and q50 = 4.66044(12) × 10-3, with the errors (1σ) on the last quoted digit. Second, a more complete set of bending levels with Σt Vt ≤ 4, some of which have never previously been reported, and also including V2 = 1 have been fitted to 80 parameters. This simultaneous fit involved 43 bands and used the same full Hamiltonian matrix. Some perturbations which affect the higher excited levels are discussed. © 1991.