High-resolution Raman spectra of acetylene, acetylene-d1, and acetylene-d2

The Raman-active fundamental bands of C2H2, C2HD, and C2D2, excited by Hg 4047 and Hg 4358 in a multiple-reflection Raman tube, were photographed with a spectral resolution of ∼0.3 cm−1. Extensive rotational structure was recorded for the ν1, ν2, and ν41 bands of C2H2 and C2D2 and the ν1 and ν2 bands of C2HD; Q branches only were obtained for the ν31 band of C2HD and the 2ν40 band of C2D2. The rotational structures were computer-analyzed to yield values of ν0, B1, D1, and q, the infrared value of B0 being assumed. From the Q branches of hot bands certain anharmonicity constants xij could be obtained. A combination of infrared and Raman data, which best satisfied a consistency test, was used to obtain the equilibrium bond lengths, re(CH) = re(CD) = 1.0605 ± 3 Å and re(CC) = 1.2033 ± 2 Å.