Microwave measurements of rotational transitions and nitrogen quadrupole coupling for 2-aminopyridine

The high-resolution microwave rotational spectrum was measured for 2-aminopyridine in the 4.5–13.2 GHz range using a pulsed beam Fourier transform microwave spectrometer. The measured transitions for the parent isotopologue in the 0⁺ vibrational state of the amino group inversion vibration were used to determine accurate rotational constants and quadrupole coupling constants for the two ¹⁴N atoms in the molecule. The molecular parameters determined for the 2-aminopyridine in 0⁺ vibrational state have the following values: A = 5780.374(1) MHz, B = 2733.5017(3) MHz, C = 1857.6768(3) MHz, 1.5χ_aa (¹⁴N₁) = 3.5789(45) MHz, 0.25(χ_bb – χ_cc) (¹⁴N₁) = 1.5033(24)MHz, 1.5χ_aa (¹⁴N₂) = -0.0958(70) MHz, and 0.25(χ_bb – χ_cc) (¹⁴N₂) = −1.1615(21) MHz. The measured quadrupole coupling constants are in excellent agreement with those calculated using different computational methods and basis sets. It is noted that the calculation using the MP2 functional with cc-pvDz basis set closely reproduces the experimental values for quadrupole coupling constants for the two ¹⁴N atoms.