The Potential Function of the Acetylene Molecule. I

A perturbation calculation is made of the anharmonicity coefficients in the vibrational energy expression of C2H2 in terms of the constants in the most general first-order and second-order perturbing potentials consistent with the geometrical symmetry of the molecule. From an analysis of the absorption spectrum, a tentative classification is made and the anharmonicity coefficients and the zeroth-order frequencies are calculated. The zeroth-order potential constants so obtained are: kCH=6.24, kCC=17.2, kCCH=—0.67 in 105 dynes/cm, compared with the values kCH=5.85, kCC=15.6, kCCH=0.028 obtained by using the observed frequencies. In the appendix the relation between bond constants and molecular structure is discussed.