The O–D stretch rovibrational spectra of N2–D2O and N2–DOH were measured and analyzed. A combination band involving the in-plane N2 bending vibration was also observed. These bands were recorded using a pulsed-slit supersonic jet expansion and a mid-infrared tunable optical parametric oscillator. The spectra were analyzed by considering the feasible tunneling motions, and transitions were fitted to independent asymmetric rotors for each tunneling state. The rotational constants of the four tunneling components of N2–D2O were retrieved for the excited vibrational states. A two order of magnitude increase in the tunneling splittings is observed for the asymmetric O–D stretch (ν3 in D2O) excitation compared to the symmetric stretch (ν1 in D2O) and to the ground vibrational state. This last finding indicates that the ν3 vibrational state is likely perturbed by a combination state that includes ν1. Finally, the observation of a local perturbation in the ν3 vibrational band, affecting the positions of few rovibrational levels, provides an experimental lower limit of the dissociation energy of the complex, D0 > 120 cm−1.
Rovibrational spectra of N 2 -H 2 O van der Waals complexes were measured in the overtone range, around the 2 OH stretching regions. The rotationally resolved (ν 1 , ν 2 , ν 3 ) ← (ν 1 , ν 2 , ν 3 ) = (2, 0, 0) ← (0, 0, 0) and (1, 0, 1) ← (0, 0, 0) vibrational bands were observed; where ν 1 , ν 2 , ν 3 are the vibrational quantum numbers of the isolated water molecule. As well, a combination band involving the (1,0,1) state and the intermolecular in-plane N 2 bending vibration will be presented. The spectra were measured using continuous wave cavity ringdown spectroscopy in a supersonic expansion, as implemented in the FANTASIO+ setup [1,2]. These spectra were analyzed by considering the feasible tunneling motions of this complex, fitted as separate asymmetric rotors for the four observed tunneling states. The tunneling splittings are discussed as a function of the vibrational state and compared with other isotopologues. The assignment of a rovibrational perturbation will also be discussed.
<p>Buffer gas cooling relies on the thermalization of a buffer gas with a surface brought to cryogenic temperatures, which in turn thermalizes the target molecules through collisions. Because this process does not rely on any particular energy pattern, any molecule can be brought to the temperature of the buffer gas. Advantages of buffer gas cooling are numerous: it is a continuous source of slow laboratory frame velocities, allowing for long observation times. Moreover, in contrast to supersonic expansion, it does not require important pumping infrastructure because it relies on small gas throughput and cryogenic pumping (Changala et al., Appl. Phys. B 122 (2016) 292). Finally, buffer gas cooling is applicable to nearly all molecules and is very efficient in terms of sample density (Santamaria et al., ApJ 801 (2015) 50). The technique requires continuous injection of helium atoms and the species under study inside a vacuum chamber. We developed a cavity ringdown spectroscopy setup to seek the first cold molecules obtained with our apparatus.</p><p>One of our first molecular targets is a six-atoms asymmetric top molecule and the smallest molecule to present internal rotation: methanol (CH<sub>3</sub>OH).<br>The size of this molecule and the presence of this large amplitude motion lead to a dense and disordered rotational structure. This structure gets even more complicated when one goes up in energy with vibrational excitations. Due to its complicated spectrum, this molecule remains poorly known, especially in the NIR. This frequency range was recently explored by Svoboda et al. (Phys. Chem. Chem. Phys., 17 (2015) 15710), probing the 2&#957;<sub>1</sub> vibration overtone around 7200 cm<sup>-1</sup>. In this report, the authors were able to assign on the order of a few percent of the observed lines. It thus seemed to be a promising candidate to challenge our ability to record and understand the spectral signature of large molecules in the overtone range using the cooling efficiency of the buffer gas cooling setup and the sensitivity of the cavity ringdown spectrometer.</p><p>The experiment and the spectra of CH<sub>3</sub>OH will be discussed. The floor will be open for discussion to identify new targets of astrophysical or atmospheric interest.</p>
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