High-resolution far-infrared synchrotron FTIR spectrum of the ν12 band of formamide-d1 (DCONH2)

Abstract

The spectrum of the ν12 band of formamide-d1 (DCONH2) was recorded using a synchrotron Fourier transform infrared (FTIR) spectrometer coupled to the Australian Synchrotron THz/Far-IR beamline, with an unapodized resolution of 0.00096 cm−1 in the 350–210 cm−1 region. For the first time, rovibrational constants up to five quartic and two sextic terms were derived for the v12 = 1 state through the fitting of a total of 2072 far-infrared transitions using Watson's A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.000073 cm−1. The band centre of the ν12 band of DCONH2 was found to be 289.3327553(47) cm−1 although the experimental uncertainty was limited to ±0.0002 cm−1. Ground state rovibrational constants of DCONH2 up to five quartic and two sextic constants were derived from a fit of 847 ground state combination differences (GSCDs) obtained from the infrared transitions of the ν12 band, together with 6 previously reported microwave transitions, with a rms deviation of 0.000108 cm−1. The ground state rotational constants (A, B, and C) of DCONH2 were improved while the ground state centrifugal distortion constants were accurately obtained for the first time. The uncertainty of the measured infrared lines was estimated to be ±0.0002 cm−1. From the ground state rotational constants, the inertial defect of DCONH2 was calculated to be 0.0169412(11) uÅ2.