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 1<i>H</i>-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 <i>J</i> and <i>K</i>. 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).