Rotation and Rotation–Vibration Spectroscopy of the 0+–0– Inversion Doublet in Deuterated Cyanamide

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 117; no. 39; pp. 9889 - 9898
• Main Authors: Kisiel, Zbigniew, Kraśnicki, Adam, Jabs, Wolfgang, Herbst, Eric, Winnewisser, Brenda P, Winnewisser, Manfred
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 03.10.2013
• Subjects: Atomic and molecular physics; Exact sciences and technology; Molecular properties and interactions with photons; Molecular spectra; Physics; Properties of molecules and molecular ions; Rotation, vibration and vibration-rotation constants; Energy levels; Rotational transition; Rotational constant; Theoretical study; Interstellar molecules; Isotopic species; Infrared spectra; Deuterium compounds; Rovibrational transition; Hamiltonians; Molecular constant; Microwave spectra; Organic compounds
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp3128687

The pure rotation spectrum of deuterated cyanamide was recorded at frequencies from 118 to 649 GHz, which was complemented by measurement of its high-resolution rotation-vibration spectrum at 8–350 cm–1. For D2NCN the analysis revealed considerable perturbations between the lowest K a rotational energy levels in the 0+ and 0– substates of the lowest inversion doublet. The final data set for D2NCN exceeded 3000 measured transitions and was successfully fitted with a Hamiltonian accounting for the 0+ ↔ 0– coupling. A smaller data set, consisting only of pure rotation and rotation-vibration lines observed with microwave techniques was obtained for HDNCN, and additional transitions of this type were also measured for H2NCN. The spectroscopic data for all three isotopic species were fitted with a unified, robust Hamiltonian allowing confident prediction of spectra well into the terahertz frequency region, which is of interest to contemporary radioastronomy. The isotopic dependence of the determined inversion splitting, ΔE = 16.4964789(8), 32.089173(3), and 49.567770(6) cm–1, for D2NCN, HDNCN, and H2NCN, respectively, is found to be in good agreement with estimates from a simple reduced quartic-quadratic double minimum potential.