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High Resolution Image Download MS PowerPoint Slide The gas-phase rotational spectrum from 85 to 750 GHz and high-resolution infrared (IR) spectrum (Canadian Light Source) of 1 H -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 (ν 21, ν 20, ν 19, and ν 18 ) 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 (ν 17, ν 16, ν 15, and ν 14 ) 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 (ν 13, ν 12, ν 11, ν 21 + ν 20, ν 21 + ν 19, and ν 21 + ν 18 ) 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).
Esselman et al. (2025) studied this question.