High-resolution FTIR measurement and analysis of the ν3 band of C2H3D

The Fourier transform infrared (FTIR) spectrum of the ν3 band of C2H3D was measured at an unapodized resolution of 0.0063 cm−1 in the 1240-1340 cm−1 region. Rovibrational constants for the upper state (ν3 = 1) up to five quartic and two sextic centrifugal distortion terms had been obtained by assigning and fitting a total of 1037 infrared transitions using a Watson's A-reduced Hamiltonian in the Ir representation. The root-mean-square deviation of the fit was 0.00051 cm−1. The ground state rovibrational constants were also determined by a fit of 674 combination differences together with 21 microwave frequencies from the present infrared measurements with a root-mean-square deviation of 0.00040 cm−1. The upper state (ν3 = 1) and ground state rovibrational constants of C2H3D represent the most accurate values obtained so far. The A-type ν3 band, centred at 1288.788826 ± 0.000044 cm−1 was found to be relatively free from local frequency perturbations. From the ν3 = 1 rovibrational constants obtained, the inertial defect Δ3 was 0.1619724 ± 0.0000001 μÅ2.