JILA, National Institute of Standards and Technology, University of Colorado, and Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309, USA.
J Chem Phys. 2018 Jan 7;148(1):014304. doi: 10.1063/1.5003230.
Sub-Doppler infrared rovibrational transitions in the symmetric (v) and antisymmetric (v) NH stretch modes of the isotopomerically substituted NDH ammonium cation are reported for the first time in a slit jet discharge supersonic expansion spectrometer. The partially H/D substituted cation is generated by selective isotopic exchange of ND with HO to form NHD, followed by protonation with H formed in the NHD/H/Ne slit-jet discharge expansion environment. Rotational assignment for NDH is confirmed rigorously by four line ground state combination differences, which agree to be within the sub-Doppler precision in the slit jet (∼9 MHz). Observation of both b-type (ν) and c-type (ν) bands enables high precision determination of the ground and vibrationally excited state rotational constants. From an asymmetric top Watson Hamiltonian analysis, the ground state constants are found to be A″ = 4.856 75(4) cm, B″ = 3.968 29(4) cm, and C″ = 3.446 67(6) cm, with band origins at 3297.5440(1) and 3337.9050(1) cm for the v and v modes, respectively. This work permits prediction of precision microwave/mm-wave transitions, which should be invaluable in facilitating ongoing spectroscopic searches for partially deuterated ammonium cations in interstellar clouds and star-forming regions of the interstellar medium.
首次在缝式射流超声速膨胀光谱仪中报道了对称（ν）和反对称（ν）NH 伸缩模式中同位素取代的 NDH 铵阳离子的亚多普勒红外转动跃迁。部分 H/D 取代的阳离子是通过 ND 与 HO 的选择性同位素交换形成 NHD，然后在 NHD/H/Ne 缝射流放电膨胀环境中质子化形成的。通过严格的四条基态组合差的转动分配，确认了 NDH 的转动分配，这些组合差在缝射流（约 9 MHz）中的亚多普勒精度内一致。b 型（ν）和 c 型（ν）带的观测使基态和振动激发态转动常数的高精度测定成为可能。从非对称顶 Watson 哈密顿分析中，发现基态常数为 A″=4.85675（4）cm、B″=3.96829（4）cm 和 C″=3.44667（6）cm，ν和 ν 模式的带起源分别为 3297.5440（1）和 3337.9050（1）cm。这项工作允许对精密微波/毫米波跃迁进行预测，这对于促进在星际云中和星际介质的恒星形成区域中对部分氘化铵阳离子的光谱搜索将是非常有价值的。
