Esselman Brian J, Zdanovskaia Maria A, Amberger Brent K, Shutter Joshua D, Owen Andrew N, Billinghurst Brant E, Zhao Jianbao, Kisiel Zbigniew, Woods R Claude, McMahon Robert J
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Canadian Light Source. Inc., University of Saskatchewan, Saskatoon, Saskatchewan S7N 2V3, Canada.
J Chem Phys. 2024 May 21;160(19). doi: 10.1063/5.0205488.
The gas-phase rotational spectrum from 8 to 750 GHz and the high-resolution infrared (IR) spectrum of pyridazine (o-C4H4N2) have been analyzed for the ground and four lowest-energy vibrationally excited states. A combined global fit of the rotational and IR data has been obtained using a sextic, centrifugally distorted-rotor Hamiltonian with Coriolis coupling between appropriate states. Coriolis coupling has been addressed in the two lowest-energy coupled dyads (ν16, ν13 and ν24, ν9). Utilizing the Coriolis coupling between the vibrational states of each dyad and the analysis of the IR spectrum for ν16 and ν9, we have determined precise band origins for each of these fundamental states: ν16 (B1) = 361.213 292 7 (17) cm-1, ν13 (A2) = 361.284 082 4 (17) cm-1, ν24 (B2) = 618.969 096 (26) cm-1, and ν9 (A1) = 664.723 378 4 (27) cm-1. Notably, the energy separation in the ν16-ν13 Coriolis-coupled dyad is one of the smallest spectroscopically measured energy separations between vibrational states: 2122.222 (72) MHz or 0.070 789 7 (24) cm-1. Despite ν13 being IR inactive and ν24 having an impractically low-intensity IR intensity, the band origins of all four vibrational states were measured, showcasing the power of combining the data provided by millimeter-wave and high-resolution IR spectra. Additionally, the spectra of pyridazine-dx isotopologues generated for a previous semi-experimental equilibrium structure (reSE) determination allowed us to analyze the two lowest-energy vibrational states of pyridazine for all nine pyridazine-dx isotopologues. Coriolis-coupling terms have been measured for analogous vibrational states across seven isotopologues, both enabling their comparison and providing a new benchmark for computational chemistry.
已对哒嗪（邻 - C₄H₄N₂）在8至750 GHz的气相转动光谱以及基态和四个最低能量振动激发态的高分辨率红外（IR）光谱进行了分析。使用具有适当状态之间科里奥利耦合的六次离心畸变转子哈密顿量，对转动和红外数据进行了联合全局拟合。在两个最低能量的耦合二元组（ν₁₆，ν₁₃和ν₂₄，ν₉）中考虑了科里奥利耦合。利用每个二元组振动状态之间的科里奥利耦合以及对ν₁₆和ν₉的红外光谱分析，我们确定了这些基态中每个基态的精确谱带起源：ν₁₆（B₁） = 361.213 292 7（17）cm⁻¹，ν₁₃（A₂） = 361.284 082 4（17）cm⁻¹，ν₂₄（B₂） = 618.969 096（26）cm⁻¹，以及ν₉（A₁） = 664.723 378 4（27）cm⁻¹。值得注意的是，ν₁₆ - ν₁₃科里奥利耦合二元组中的能量间隔是光谱测量的振动状态之间最小的能量间隔之一：2122.222（72）MHz或0.070 789 7（24）cm⁻¹。尽管ν₁₃是红外非活性的，且ν₂₄的红外强度低到不实用，但仍测量了所有四个振动状态的谱带起源，展示了结合毫米波和高分辨率红外光谱提供的数据的强大作用。此外，为先前的半实验平衡结构（reSE）测定生成的哒嗪 - dx同位素异构体的光谱，使我们能够分析所有九个哒嗪 - dx同位素异构体的哒嗪的两个最低能量振动状态。已测量了七个同位素异构体中类似振动状态的科里奥利耦合项，这既便于它们之间的比较，也为计算化学提供了一个新的基准。
