First high-resolution low-temperature spectrum of the $2{\nu }_{\text{OH}}$ overtone of trans-formic acid have been measured using direct-absorption laser spectroscopy. The supersonic cooling in the jet expansion to 37 K has dramatically simplified the complex ro-vibrational structure of the band due to the thermal depopulation of higher-lying rotational states. Altogether, 597 lines have been measured with a line-position accuracy better than 0.001 cm${}^{-1}$, and 441 of them have been reliably assigned using a custom-build program for a line-by-line assignment using the ground state combination differences. In total, 39 low-lying upper rotational states of the overtone vibration have been calculated from these line assignments. Moreover, some additional states have been also identified and tentatively assigned to a bath of dark states present in this spectral region. A global fit using A-reduced Watson’s type Hamiltonian in $I^r$ representation has been performed to obtain several ro-vibrational constants for the $2{\nu }_{\text{OH}}$ vibration. In addition, the fit demonstrates the effect of numerous perturbations in the rotational structure.

首个高分辨率低温光谱$2{\nu }_{\text{哦}}$使用直接吸收激光光谱法测量了反式甲酸的泛音。射流膨胀到 37 K 时的超音速冷却极大地简化了带的复杂旋转振动结构，这是由于较高旋转状态的热减少。总共测量了 597 条线，线位置精度优于 0.001 厘米${}^{-1}$，其中 441 个已使用自定义构建程序可靠地分配，使用基态组合差异进行逐行分配。总共从这些线分配中计算了 39 个低位的泛音振动的上旋转状态。此外，还确定了一些其他状态，并暂时将其分配给该光谱区域中存在的暗状态浴。使用 A-reduced Watson 类型 Hamiltonian 的全局拟合${我}^r$已经进行了表示以获得几个旋转振动常数$2{\nu }_{\text{哦}}$振动。此外，拟合证明了旋转结构中许多扰动的影响。