Millimeter-Wave and High-Resolution Infrared Spectroscopy of the Ground and 14 Vibrationally Excited States Lying Below 1300 cm–1 of Pyrazole

The gas-phase rotational spectrum from 85 to 750 GHz and high-resolution infrared (IR) spectrum (Canadian Light Source) of 1H-pyrazole have been analyzed for the ground and vibrationally excited states lying below 1300 cm–1. The analysis benefits from the simultaneous analysis of rotational and high-resolution IR transitions that cover the same approximate ranges of J and K. In total, over 4400 transitions for the ground state have been measured, assigned, and least-squares fit to complete sextic centrifugally distorted-rotor Hamiltonian models. The presented ground-state rotational spectrum provides the foundation for astronomical searches across most of the frequency range covered by modern radiotelescopes. Additionally, the rotational and high-resolution infrared transitions of the 11 lowest-energy fundamental and three lowest-energy combination states have been measured, assigned, and least-squares fit. The four lowest-energy fundamental states (ν21, ν20, ν19, and ν18) are sufficiently separated in energy that they can all be well-treated by single-state Hamiltonians across the entire measured spectrum. The next four lowest-energy fundamental states (ν17, ν16, ν15, and ν14) form a Coriolis-coupled tetrad of states that are fit to a four-state model with six Coriolis interactions. The remaining vibrationally excited states investigated in this work (ν13, ν12, ν11, ν21 + ν20, ν21 + ν19, and ν21 + ν18) are treated by effective Hamiltonians, owing to their complex anharmonic- and Coriolis-coupling interactions. The experimental spectroscopic constants and vibrational energies are compared to their computed values (CCSD(T)/cc-pCVTZ).