Cavity-enhanced frequency comb spectroscopy for molecule detection in themid-infrared powerfully combines high resolution, high sensitivity, and broadspectral coverage. However, this technique, and essentially all spectroscopicmethods, is limited in application to relatively small, simple molecules. Herewe integrate comb spectroscopy with continuous, cold samples of moleculesproduced via buffer gas cooling, thus enabling the study of significantly morecomplex molecules. We report simultaneous gains in resolution, sensitivity, andbandwidth and demonstrate this combined capability with the first rotationallyresolved direct absorption spectra in the CH stretch region of several complexmolecules. These include nitromethane (CH$_3$NO$_2$), a model system thatpresents challenging questions to the understanding of large amplitudevibrational motion, as well as several large organic molecules with fundamentalspectroscopic and astrochemical relevance, including naphthalene(C$_{10}$H$_8$), adamantane (C$_{10}$H$_{16}$), and hexamethylenetetramine(C$_{6}$N$_4$H$_{12}$). This general spectroscopic tool has the potential tosignificantly impact the field of molecular spectroscopy, simultaneouslyimproving efficiency, spectral resolution, and specificity by orders ofmagnitude. This realization could open up new molecular species and newkinetics for precise investigations, including the study of complex molecules,weakly bound clusters, and cold chemistry.
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机译：用于中红外分子检测的腔增强频率梳光谱技术将高分辨率，高灵敏度和宽光谱覆盖范围强大地结合在一起。然而，该技术以及基本上所有的光谱方法都限于相对较小的简单分子的应用。在这里，我们将梳状光谱与通过缓冲气体冷却产生的连续冷样品分子结合在一起，从而使研究复杂得多的分子成为可能。我们报告了分辨率，灵敏度和带宽的同时增长，并证明了这种结合的能力与几种复杂分子的CH拉伸区中的第一个旋转分辨直接吸收光谱。其中包括硝基甲烷（CH $ _3 $ NO $ _2 $），这是一个模型系统，它对理解大振幅振动运动提出了具有挑战性的问题，以及几种具有基本光谱和天化学相关性的大有机分子，包括萘（C $ _ {10} $ H $ _8 $），金刚烷（C $ _ {10} $ H $ _ {16} $）和六亚甲基四胺（C $ _ {6} $ N $ _4 $ H $ _ {12} $）。这种通用的光谱工具有可能极大地影响分子光谱学领域，同时以数量级提高效率，光谱分辨率和特异性。这一认识可以为精确的研究开辟新的分子种类和新动力学，包括研究复杂分子，弱结合簇和冷化学。
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