Infrared spectra of CHD 2Cl and CHD 2CCH and the geometries of methyl chloride and propyne

Abstract

Five type B or type C bands in the gas phase infrared spectrum of CHD 2Cl and two type C bands of CHD 2CCH have been analyzed with a resolution of 0.2 cm −1. All other fundamental vibrations have been located. Accurate determinations of ( A 0- B 0 ) for each molecule are obtained from ground state combination differences, from which A 0 values are derived using microwave estimates of B 0 and C 0. The combination of one A 0 rotational constant with B 0 and C 0 constants for all other isotopic species enables the ground state molecular geometry to be fixed within narrow limits, assuming that zero-point energy effects cause a shortening of the CH bond length by 0.002 Å on deuteration. The CH bond lengths are in almost precise agreement with the values predicted from the position of the sole CH stretching vibration frequency for each molecule.