Abstract Formamidinium formate occurs in the gas phase as a doubly hydrogen-bonded dimer. New high-level calculations on formamidinium formate using various methods and basis sets are described. The calculated rotational constants and quadrupole coupling constants given here are reasonably consistent between the different methods and in reasonably good agreement with values obtained from the new analysis of the microwave data. In the revised fit 38 measured transitions are fit with a standard deviation of 30 kHz. The revised rotational, centrifugal distortion and quadrupole coupling constants determined from the spectra have values: A = 5890.39(8), B = 2148.731(1), C = 1575.0958(8), 1.5 χaa (N1) = 2.254(24), 0.25(χbb - χcc)(N1) = 1.747(12), 1.5χaa (N2) = -3.134(29), 0.25(χbb - χcc)(N2) = 0.553(10) MHz. The calculated rotational constants which agree best with experiment are from an M11 /def2-QZVPP calculation: A = 5785.29, B = 2143.25and C = 1563.88 MHz. The calculated quadrupole coupling constants which agree best with experiment are from a PBE0 aug-cc-pVQZ (uncontracted) calculation: 1.5 χaa (N1) = 1.78, 0.25(χbb - χcc)(N1) = 1.49, 1.5χaa (N2) = -3.41), 0.25(χbb - χcc)(N2) = 0.51 MHz. The calculated rotational constants agree within 2%, and quadrupole coupling constants within 11% or better with the experimental values.

中文翻译：

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甲脒的计算分子性质和微波光谱分析

摘要 甲脒以双氢键二聚体形式存在于气相中。描述了使用各种方法和基组对甲酸甲脒进行新的高级计算。这里给出的计算旋转常数和四极耦合常数在不同方法之间相当一致，并且与从微波数据的新分析中获得的值相当吻合。在修订后的拟合中，38 个测量的转换以 30 kHz 的标准偏差拟合。由光谱确定的修正旋转、离心畸变和四极耦合常数具有以下值：A = 5890.39(8), B = 2148.731(1), C = 1575.0958(8), 1.5 χaa (N1) = 2.254(24), 0.25 (χbb - χcc)(N1) = 1.747(12), 1.5χaa (N2) = -3.134(29), 0.25(χbb - χcc)(N2) = 0.553(10) MHz。与实验最相符的计算旋转常数来自 M11 /def2-QZVPP 计算：A = 5785.29，B = 2143.25 和 C = 1563.88 MHz。与实验最相符的计算出的四极耦合常数来自 PBE0 aug-cc-pVQZ（未收缩）计算：1.5 χaa (N1) = 1.78, 0.25(χbb - χcc)(N1) = 1.49, 1.5χaa (N2) = -3.41), 0.25(χbb - χcc)(N2) = 0.51 MHz。计算的旋转常数与实验值一致在 2% 以内，四极耦合常数在 11% 以内或更好。25(χbb - χcc)(N2) = 0.51 MHz。计算的旋转常数与实验值一致在 2% 以内，四极耦合常数在 11% 以内或更好。25(χbb - χcc)(N2) = 0.51 MHz。计算的旋转常数与实验值一致在 2% 以内，四极耦合常数在 11% 以内或更好。