Bunn Hayley A, Zdanovskaia Maria A, Billinghurst Brant E, Zhao Jianbao, Widicus Weaver Susanna L, Woods R Claude, McMahon Robert J, Esselman Brian J
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
Canadian Light Source. Inc., University of Saskatchewan, Saskatoon, Saskatchewan S7N 2 V3, Canada.
J Phys Chem A. 2024 Aug 22;128(33):6927-6942. doi: 10.1021/acs.jpca.4c03890. Epub 2024 Aug 9.
A combined analysis of millimeter-wave (70-700 GHz) and rotationally resolved infrared (400-1200 cm) spectra of the ground state and seven fundamental vibrational modes of 1-1,2,4-triazole is reported. While the lowest-energy vibrationally excited state (ν) is well-treated using a single-state distorted-rotor Hamiltonian, the second (ν) and third (ν) vibrationally excited states are involved in strong -type Coriolis coupling and require an appropriate two-state Hamiltonian. The oblate nature of 1-1,2,4-triazole is sufficiently close to the oblate symmetric-top limit that the analysis requires the use of A-reduced, sextic centrifugally distorted-rotor Hamiltonian models in the I representation in order to achieve low σ values. The coupling between ν (A″) and ν (A″) resulted in many transitions with slightly perturbed frequencies, many highly displaced resonant intrastate transitions, and 165 nominal interstate transitions. Modeling the spectra of ν and ν required three -axis Coriolis-coupling terms (, , and ) to treat the interaction. Many of the nominal interstate transitions form clearly discernible Q-branch bands, comprising degenerate sets of - and -type transitions. The rotational spectra of four higher-energy vibrationally excited states (ν, ν, ν, and ν), which form a complex polyad involving Coriolis and anharmonic coupling interactions, were analyzed by single-state models, thus producing only effective spectroscopic constants. Inclusion of rotationally resolved infrared transitions enabled the accurate and precise determination of vibrational band origins for the four lowest-energy fundamental states: ν = 542.601 824 3 (28) cm, ν = 665.183 128 5 (43) cm, ν = 682.256 910 5 (43) cm, and ν = 847.557 400 (11) cm.
报道了对1,2,4 - 三唑基态及七种基本振动模式的毫米波（70 - 700吉赫兹）和转动分辨红外（400 - 1200厘米）光谱的联合分析。虽然使用单态扭曲转子哈密顿量能很好地处理最低能量的振动激发态（ν），但第二（ν）和第三（ν）振动激发态涉及强型科里奥利耦合，需要合适的双态哈密顿量。1,2,4 - 三唑的扁球形足够接近扁球对称陀螺极限，以至于分析需要在I表象中使用A约化的六次离心扭曲转子哈密顿量模型以获得低σ值。ν（A″）和ν（A″）之间的耦合导致许多频率略有扰动的跃迁、许多高度位移的共振态内跃迁以及165个标称的态间跃迁。对ν和ν光谱进行建模需要三轴科里奥利耦合项（、和）来处理相互作用。许多标称的态间跃迁形成清晰可辨的Q支带，由简并的 - 型和 - 型跃迁组组成。通过单态模型分析了四个高能振动激发态（ν、ν、ν和ν）的转动光谱，它们形成了一个涉及科里奥利和非谐耦合相互作用的复杂多重组，从而仅产生有效的光谱常数。包含转动分辨红外跃迁使得能够准确精确地确定四个最低能量基本态的振动带起源：ν = 542.601 824 3（28）厘米，ν = 665.183 128 5（43）厘米，ν = 682.256 910 5（43）厘米，以及ν = 847.557 400（11）厘米。
