Vibrationally excited states of 1H- and 2H-1,2,3-triazole isotopologues analyzed by millimeter-wave and high-resolution infrared spectroscopy with approximate state-specific quartic distortion constants

In this work, we present the spectral analysis of 1H- and 2H-1,2,3-triazole vibrationally excited states alongside provisional and practical computational predictions of the excited-state quartic centrifugal distortion constants. The low-energy fundamental vibrational states of 1H-1,2,3-triazole and five of its deuteriated isotopologues ([1-H-2]-, [4-H-2]-, [5-H-2]-, [4,5-H-2]-, and [1,4,5-H-2]-1H-1,2,3-triazole), as well as those of 2H-1,2,3-triazole and five of its deuteriated isotopologues ([2-H-2]-, [4-H-2]-, [2,4-H-2]-, [4,5-H-2]-, and [2,4,5-H-2]-2H-1,2,3-triazole), are studied using millimeter-wave spectroscopy in the 130-375 GHz frequency region. The normal and [2-H-2]-isotopologues of 2H-1,2,3-triazole are also analyzed using high-resolution infrared spectroscopy, determining the precise energies of three of their low-energy fundamental states. The resulting spectroscopic constants for each of the vibrationally excited states are reported for the first time. Coupled-cluster vibration-rotation interaction constants are compared with each of their experimentally determined values, often showing agreement within 500 kHz. Newly available coupled-cluster predictions of the excited-state quartic centrifugal distortion constants based on fourth-order vibrational perturbation theory are benchmarked using a large number of the 1,2,3-triazole tautomer isotopologues and vibrationally excited states studied.

Automated summary

In this work, the spectral analysis of 1H- and 2H-1,2,3-triazole vibrationally excited states is presented, along with computational predictions of the excited-state quartic centrifugal distortion constants. The fundamental vibrational states of 1H- and 2H-1,2,3-triazole and their isotopologues are studied using millimeter-wave and high-resolution infrared spectroscopy. The spectroscopic constants for each of the vibrationally excited states are reported for the first time, and the coupled-cluster predictions of the excited-state quartic centrifugal distortion constants are benchmarked.