The 130–500 GHz rotational spectroscopy of cyanopyrazine (C4H3N2-CN)

Abstract

The rotational spectrum of cyanopyrazine (2-pyrazinecarbonitrile, p-C4H3N2-CN) has been obtained from 130 to 500 GHz. Rotational transitions of cyanopyrazine have been measured, assigned, and least-squares fit for the first time. Over 7000 transitions of the ground vibrational state have been least-squares fit to partial octic, A- and S-reduced Hamiltonians with low statistical uncertainty (σfit = 34 kHz). Similar to other cyanoarenes, the first two fundamental modes are the out-of-plane (ν27, A′′) and in-plane (ν19, A′) nitrile bending modes, which form an a- and b-axis Coriolis-coupled dyad. Greater than 5800 transitions from each of these vibrational modes were fit to a partial octic, A-reduced Hamiltonian (σfit = 38 kHz), and the analysis reveals the precise energy separation, ΔE27,19, between the coupled vibrational states, as well as values for eight a- and b-type Coriolis-coupling coefficients, Ga, GaJ, GaK, GaJJ, FbcK, Gb, GbJ, and Fac. Cyanopyrazine is a strongly polar derivative of pyrazine, thus cyanopyrazine can serve as a potential tracer molecule for its nonpolar parent compound in extraterrestrial environments. The transition frequencies and spectroscopic constants provided in this work, combined with theoretical or experimental nuclear quadrupole coupling constants, provide the foundation for future radioastronomical searches for cyanopyrazine.