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The intermolecular interactions involving the water molecule play important roles in many fields of physics, chemistry, and biology. High-resolution spectroscopy of Van der Waals complexes formed by a rare gas atom and a water molecule could provide a wealth of information on these intermolecular interactions. The precise experimental data can be used to test the accuracy and efficiency of various theoretical methods for constructing the intermolecular potential energy surfaces and calculating the bound states. In this work, the high-resolution infrared absorption spectrum of the Ar-D₂O complex in the <em>v</em>₂ bending region of D₂O was measured using an external cavity quantum cascade laser. A segmented rapid-scan data acquisition method was employed. The Ar-D₂O compex was generated in a slit supersonic jet expansion by passing Ar gas through a vessel containing liquid D₂O. Four new rovibrational subbands are assigned in the spectral range of 1150-1190 cm^-1, namely <img src="20221728_O_editing.files/image059.png" alt="" />，<img src="20221728_O_editing.files/image094.png" alt="" />，<img src="20221728_O_editing.files/image090.png" alt="" /> and <img src="20221728_O_editing.files/image091.png" alt="" />. The first two subbands belong to the <em>otho</em>- species of Ar-D₂O, while the latter two belong to the <em>para</em>- species. The observed rovibrational transitions together with the previously reported pure rotational spectra having the common lower vibrational sub-states are analyzed by a weighted least-squares fitting using a pseudo-diatomic effective Hamiltonian. An experimental error of 10 kHz for the far-infrared transitions and 0.001 cm^-1 for the infrared transitions was set in the global fitting when using Pickett’s program SPFIT, respectively. Molecular constants including vibrational substate energies, rotational and centrifugal distortion constants, and Coriolis coupling constant, are determined accurately. The previous results for the <img alt="" /> substate are found to be likely wrong. The energies of the <img src="20221728_O_editing.files/image081.png" alt="" />和<img alt="" />substates are determined experimentally for the first time. The band origin of Ar-D₂O in the D₂O <em>v</em>₂ bending mode region is determined to be 1177.92144(13) cm^-1, which is red-shifted from that of D₂O monomer by about 0.458 cm^-1. The experimental vibrational substate energies are compared with their theoretical values based on a four-dimensional intermolecular potential energy surface which includes the normal coordinate of the D₂O <em>v</em>₂ bending mode. The experimental and theoretical results are in good agreement with each other. But the calculated energy levels are generally higher than the experimental values so the theoretical calculations still have the space to be improved.

Sulfur hexafluoride (SF_６) is a greenhouse gas of very long lifetime. Its infrared absorption spectrum is very important for modeling the atmospheric radiation balances. SF_６ is also a prototypical system for studying the principles and techniques of laser isotope separation using powerful infrared lasers. As a very heavy molecule, the infrared spectrum of SF_６ at room temperature is very dense, which poses a great challenge for monitoring the relative abundances of different SF_６ isotopomers by direct absorption spectroscopy. Supersonic jet expansions have been used widely to simplify gas phase molecular spectra. In this work, astigmatic multi-pass absorption cell and distributed feed-back quantum cascade lasers (QCLs) are used to measure jet-cooled rovibrational absorption spectrum of ³²SF_６ and ³³SF_６ at 10.6 μm. The spectrometer works in a segmented rapid-scan mode. The gas mixtures (SF₆:Ar:He = 0.12:1:100) are expanded through a 80 mm×300 μm pulsed slit nozzle. Two QCLs running at room temperature are used and each one covers a spectral range of about 3.0 cm^-1. The <i>v</i>₃ fundamental bands of both ³²SF_６ and ³³SF_６ are observed. The rotational temperature of ³²SF_６ and ³³SF_６ in the ground state in the supersonic jet is estimated to be about 10 K and the linewidth is about 0.0008 cm^-1 by comparing the simulated and observed spectrum with the PGOPHER program. A new weak vibrational band centered around 941.0 cm^-1 is observed and tentatively assigned to the <i>v</i>₁+<i>v</i>₂+<i>v</i>₃-(<i>v</i>₁+<i>v</i>₂)hot band of ³²SF_６. The effective Hamiltonian used to analyze the rovibrational spectrum of SF_６ is briefly introduced. A simplified rotational analysis for this hot band is performed with the XTDS program developed by the Dijon group. The band-origin of this hot band is determined to be 941.1785(21) cm^-1. The rotational temperature of this hot band is estimated to be about 50 K. A new scheme by measuring the jet-cooled absorption spectrum of this hot band of ³²SF₆ and the <i>v</i>₃ fundamental band of ³³SF_６ is proposed for measuring the relative abundance of ³³SF_６／³²SF_６.