ROVIBRATIONAL SPECTROSCOPIC CONSTANTS AND FUNDAMENTAL VIBRATIONAL FREQUENCIES FOR ISOTOPOLOGUES OF CYCLIC AND BENT SINGLET HC2N ISOMERS.

Through established, highly accurate ab initio quartic force fields, a complete set of fundamental vibrational frequencies, rotational constants, and rovibrational coupling and centrifugal distortion constants have been determined for both the cyclic 1 ¹A′ and bent 2 ¹A′ DCCN, H¹³CCN, HC¹³CN, and HCC¹⁵N isotopologues of HCCN. Spectroscopic constants are computed for all isotopologues using second-order vibrational perturbation theory (VPT2), and the fundamental vibrational frequencies are computed with VPT2 and vibrational configuration interaction (VCI) theory. Agreement between VPT2 and VCI results is quite good, with the fundamental vibrational frequencies of the bent isomer isotopologues in accord to within a 0.1-3.2 cm^–1 range. Similar accuracies are present for the cyclic isomer isotopologues. The data generated here serve as a reference for astronomical observations of these closed-shell, highly dipolar molecules using new, high-resolution telescopes and as reference for laboratory studies where isotopic labeling may lead to elucidation of the formation mechanism for the known interstellar molecule: X³A′ HCCN. [ABSTRACT FROM AUTHOR]