物理
原子物理学
转动惯量
旋转振动光谱学
偶极子
分光计
四极
分子物理学
光学
激发态
量子力学
标识
DOI:10.1016/0032-0633(85)90042-x
摘要
The rotation-torsion spectrum of carbodiimide, HNCNH, a constituent of the vapor of cyanamide, H2NCN, was measured in the region from 15 GHz to 330 cm−1 using a high-resolution Fourier transform spectrometer, a laser single-sideband spectrometer, a millimeter-wave and a submillimeter-wave spectrometer. Aside from a small doublet splitting (<0.016 cm−1) detected for most of the transitions, the spectral pattern of a perpendicular band, expected for skew-chain molecules, was observed. The principal axis b of the inertia tensor is parallel to the C2 symmetry axis of HNCNH. The molecular constants obtained by fitting the positions of the doublet centers with Watson's Hamiltonian in S-reduction are A = 379 244.493(27)MHz, B = 10 366.9389(18)MHz, and C = 10 366.0837(25)MHz, which yield κ = −0.999995368(18). The small splittings were found to be due to a torsional motion. The analysis of the unusual dependence of the torsional splitting on Ka allows the calculation of the torsional energy separations ΔEtrans and ΔEcis in the vibrational ground state. On the basis of these separations we can conclude that the cis and the trans barriers must have approximately the same height. The strong dependence of the torsional splittings on Ka indicates a large rotation-HNC bending interaction affecting the effective barriers Vcis and Vtrans hindering internal rotation. The permanent electric dipole moment was determined to be 1.90(5) D. From the relative intensities of the a-type rotational transitions of cyanamide and the b-type rotational-torsional transitions of carbodiimide it was found that the abundance ratio of carbodiimide to cyanamide at 380 K is 1115(14). This work provides an extensive high precision data base for HNCNH, making a radioastronomical search for this molecule possible.
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