Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Institute for Theoretical Chemistry, Departments of Chemistry and Biochemistry, The University of Texas-Austin, Austin, Texas 78712, USA.
J Chem Phys. 2013 Dec 14;139(22):224304. doi: 10.1063/1.4832899.
The rotational spectrum of pyridazine (o-C4H4N2), the ortho disubstituted nitrogen analog of benzene, has been measured and analyzed in the gas phase. For the ground vibrational state of the normal isotopolog, over 2000 individual rotational transitions have been identified between 238 and 360 GHz and have been fit to 13 parameters of a 6th-order centrifugal distortion Hamiltonian. All transitions in this frequency region can now be predicted from this model to near experimental accuracy, i.e., well enough for the purpose of any future radio-astronomical search for this species. Three isotopologs, [3-(13)C]-C4H4N2, [4-(13)C]-C4H4N2, and [1-(15)N]-C4H4N2, have been detected in natural abundance, and several hundred lines have been measured for each of these species and fit to 6th-order Hamiltonians. Ten additional isotopologs were synthesized with enhanced deuterium substitution and analyzed to allow for a complete structure determination. The equilibrium structure (Re) of pyridazine was obtained by correcting the experimental rotational constants for the effects of vibration-rotation coupling using interaction constants predicted from CCSD(T) calculations with an ANO0 basis set and further correcting for the effect of electron mass. The final Re structural parameters are determined with excellent accuracy, as evidenced by their ability to predict 28 independent moments of inertia (Ia and Ib for 14 isotopologs) very well from 9 structural parameters. The rotational spectra of the six lowest-energy fundamental vibrational satellites of the main isotopolog have been detected. The rotational spectra of the five lowest-energy vibrational satellites have been assigned and fit to yield accurate rotational and distortion constants, while the fit and assignment for the sixth is less complete. The resultant vibration-rotation interaction (α) constants are found to be in excellent agreement with ones predicted from coupled-cluster calculations, which proved to be the key to unambiguous assignment of the satellite spectra to specific vibration modes.
哒嗪（o-C4H4N2）的旋转光谱已在气相中进行了测量和分析，哒嗪是苯的邻位取代氮类似物。对于正常同位素的基频振动态，在 238 至 360GHz 之间已鉴定出超过 2000 个单独的旋转跃迁，并已拟合到六阶离心扭曲哈密顿量的 13 个参数。在该频率范围内的所有跃迁现在都可以通过该模型预测到接近实验精度，即足以满足未来对该物种的任何射电天文搜索目的。已在天然丰度下检测到三个同位素，[3-(13)C]-C4H4N2、[4-(13)C]-C4H4N2 和 [1-(15)N]-C4H4N2，并且已经为每种同位素测量了几百条线，并拟合到六阶哈密顿量。另外十个同位素是通过增强氘取代合成的，并进行了分析，以实现完整的结构测定。通过使用基于 ANO0 的 CCSD(T)计算和进一步校正电子质量的影响来预测相互作用常数，从而校正振动-旋转耦合对实验旋转常数的影响，得到了哒嗪的平衡结构（Re）。最终的 Re 结构参数具有出色的准确性，这可以通过它们从 9 个结构参数很好地预测 28 个独立的转动惯量（14 个同位素的 Ia 和 Ib）来证明。已检测到主要同位素的六个最低能量基本振动卫星的旋转光谱。已分配并拟合了五个最低能量振动卫星的旋转光谱，以得出准确的旋转和扭曲常数，而第六个的拟合和分配则不太完整。发现振动-旋转相互作用（α）常数与耦合簇计算预测的常数非常吻合，这证明了将卫星光谱明确分配给特定振动模式的关键。
