The high sensitivity of our experimental setup (SPIRALES) [1] which couples an external cavity quantum cascade laser tunable from 1620 to 1690 cm⁻¹to a pulsed jet enabled the recording of a series of rovibrational transitions of Kr-H₂O van der Waals (vdW) complex. As for the Ar-H₂O complex [2], the barriers to internal rotation in the Kr-H₂O complex states are comparable to the H₂O rotational constants and so the H₂O subunit behaves like a nearly free internal rotor [3]. The quantum number K is used for describing the projection of J onto the vdW axis, with K = 0 for Σ, K = 1 for Π, etc. A previous jet-cooled microwave study [4] evidenced that the ground vibrational state involves 2 internal rotor states corresponding to different spin modifications, namely a para state Σ(0₀₀) and an ortho state Σ(1₀₁). The present work reports the observation of two new bands around 1634.5 cm⁻¹and 1659.7 cm⁻¹which can be interpreted according to a pseudo-atomic model. By analogy with Ar-H₂O bands observed in the same regions [2], the Kr-H₂O ones are tentatively assigned to para Π(1₁₁) ← Σ(0₀₀) and ortho Π(2₁₂) ← Σ(1₀₁) transitions, respectively, confirmed by the presence of Q branches. The ortho band displays strongly unequal spacings characteristic of a Coriolis coupling between Σ and Π states in vibrational excited states. c0pt Figure Moreover the high resolution achieved with the SPIRALES set-up allowed the observation of several isotopes of Kr. The analysis of these two bands and further investigations in the 1580-1620 cm⁻¹region are undergoing. References : [1] P. Asselin , A. Potapov, A. C. Turner, V. Boudon, L. Bruel, M.-A. Gaveau, M. Mons. PCCP 19, 17224-17232 (2017). [2] X. Liu , Y. Xu. J. Mol. Spectr. 301, 1-8 (2014). [3] R.C. Cohen , K . L . Busarow , Y. T. Lee, R. J. Saykally. JCP, 92, 169-177 (1990). [4] J. Van Wijngaarden, W. Jäger. Mol. Phys. 98, 19,1575-1588 (2000).

Weakly-bound H₂O-CO has a planar structure with approximately co-linear heavy atoms (O, C, O) and a hydrogen bond between the water and the carbon of the CO. Proton tunneling (H atom interchange) gives rise to two states corresponding to distinct nuclear spin modifications. The magnitude of the splitting in the ground rotational state is about 0.8 cm⁻¹for H₂O-CO and 0.04 cm⁻¹for D₂O-CO. Due to the almost linear heavy atom configuration, H₂O-CO has a large A rotational constant, equal to about 19 cm⁻¹(12 cm⁻¹for D₂O-CO), so the K quantum number is highly significant. Water-CO was first studied in the microwave and millimeter regions. Infrared spectra have been observed in the regions of the C-O stretch, the O-H stretch, the D₂O bend, and the H₂O bend. Here we study the O-D stretch region (3.6 μm) for the first time, observing D₂O-CO, HOD-CO, and DOH-CO. We also extend the C-O stretch region results to include the K = 1 ← 0 subbands, thus determining A rotational constants for the v(CO) = 1 excited state. But more significantly, we also observe additional K = 1 ← 0 combination bands in both regions which involve the lowest intermolecular vibration of water-CO. This mode, which lies at 43 – 49 cm⁻¹depending on isotopologue, can be identified as the in-plane CO bend. It is observed for H₂O-CO, D₂O-CO, and HOD-CO, and exhibits anomalous isotope shifts: even though their A-values are quite different, the D₂O-CO mode is only slightly lower in energy than that of H₂O-CO. Detailed rotational energy level calculations, based on a recent high-level ab initio potential energy surface Y. N. Kalugina, A. Faure, A. van der Avoird, K. Walker, and F. Lique, Phys. Chem. Chem. Phys. 20, 5469 (2018). are in good agreement with experiment, including the newly observed intermolecular mode. As well, the calculations show that the unobserved K = 0 level of this mode lies above the observed K = 1 level, thus explaining the anomalous isotope shifts.

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Y. N. Kalugina, A. Faure, A. van der Avoird, K. Walker, and F. Lique, Phys. Chem. Chem. Phys. 20, 5469 (2018).,

The internal rotations about the single bonds connecting OH or NH₂ groups to cyclopropyl or cyclopropene rings were investigated. The experimental fits to the infrared data of the one-dimensional torsional potential energy functions were compared to theoretical calculations. MP2/cc-pVTZ and CCSD/cc-pVTZ computations were found to be in good agreement with the experimental results for cyclopropanol and cyclopropylamine. Calculations were also carried out on the internal rotations of 1-cyclopropen-1-ol and 2-cyclopropen-1-amine. Each of these molecules has a calculated energy minimum corresponding to a conformation with an intramolecular π-type hydrogen bond. The π-bonding stabilization is 2.3 kcal/mol for the alcohol and 2.5 kcal/mol for the amine. The calculated O-H, N-H, and C=C stretching frequencies are lower for the hydrogen bonded conformers than for the conformations without the π-type hydrogen bonds. The C=C bond stretching frequencies show the largest decreases resulting from the hydrogen bonding.

We report observation of new infrared bands of (CS₂)₂ and (CS₂)₃ in the region of the CS₂ ν₁ + ν₃ combination band (at 4.5 μm) using a quantum cascade laser. The complexes are formed in a pulsed supersonic slit-jet expansion of a gas mixture of carbon disulfide in helium. We have previously shown that the most stable isomer of (CS₂)₂ is a cross-shaped structure with D_2d symmetry and that for (CS₂)₃ is a barrel-shaped structure with D₃ symmetry. The dimer has one doubly degenerate infrared-active band in the ν₁ + ν₃ region of the CS₂ monomer. This band is observed to have a rather small vibrational shift of -0.846 cm⁻¹. We expect one parallel and one perpendicular infrared-active band for the trimer but observe two parallel and one perpendicular bands. Much larger vibrational shifts of -8.953 cm⁻¹for the perpendicular band and -8.845 cm⁻¹and +16.681 cm⁻¹for the parallel bands are observed. Vibrational shifts and possible vibrational assignments, in the case of the parallel bands of the trimer, are discussed using group theoretical arguments.

Electrochemical reactions play important roles in chemical energy conversion. However, the surface reactions that govern these processes are not well understood because of the difficulties associated with accessing the electrode/electrolyte interface and making chemically specific measurements with interface sensitivity. Vibrational spectroscopy offers the required chemical specificity and can be used to elucidate reaction pathways based on the formation of key functional groups along a reaction coordinate. However, the challenge is to implement infrared spectroscopy as a surface sensitive probe at the electrode/electrolyte interface. Vibrational sum frequency generation spectroscopy is an inherently interface specific technique, but most people who study electrode/electrolyte interfaces employ a thin film of electrolyte which leads to wavelength-dependent attenuation of the infrared field and also presents mass transport limitations when seeking to probe electrocatalytic reaction kinetics. We present a method to overcome these limitations with high signal quality and under conditions that are compatible with electrocatalysis at high current densities. Under these conditions we study CO2 reduction on polycrystalline gold thin films and gold nanoparticles which show faradaic efficiencies for carbon monoxide of  20% and  60% respectively. We identify possible reasons for the observed difference in selectivity.

We report the infrared spectrum of C₄H₂-(OCS)₂ trimer in the region of the ν₁ fundamental vibration of the OCS monomer. The van der Waals complexes are generated in a supersonic slit-jet apparatus and probed using a rapid-scan tunable diode laser. Both C₄H₂-(OCS)₂ and C₄D₂-(OCS)₂ are studied. Analysis of their spectra establishes that the trimer has C₂ symmetry. Theoretical calculations performed to find stationary points on the potential energy surface confirm that the experimental structure is the most stable form of the trimer. The rotational parameters computed using double hybrid functionals are in very good agreement with those obtained from the observed spectra.

Superfluid helium nanodroplets are particularly useful for synthesizing molecular complexes, and several investigations have focused on investigating the hydration of atmospherically important molecules, such as the hydroxyl radical [1]. While carbonyl sulphide is the most abundant sulphur containing molecule in the atmosphere, little is known experimentally about how it interacts with water. In this study we focus on isolating OCS-(H₂O)_N complexes in helium nanodroplets, and on uncovering their infrared signatures with quantum cascade laser spectroscopy. For the dimer, we identified two isomers, which is consistent with what was observed in solid neon [2]. One of the isomers has C_s symmetry with the water near the oxygen end of OCS, and the other has C_2v symmetry, with the water at the sulphur end. The latter isomer displays well resolved rotational substructure in its C-O stretching band, and Stark spectroscopy has been performed, which should allow for determination of its dipole moment. Larger clusters seem to build off of the dimers, as evidenced by two sets of infrared bands that grow in with increasing water concentrations, near the corresponding OCS-H₂O bands. [1] F. J. Hernandez et al. The Journal of Chemical Physics 143, 164304 (2015). [2] P. Soulard et al. The Journal of Chemical Physics 146, 234303 (2017).

Matrix isolation infrared spectroscopy was used to characterize a 1:1 complex of hydrogen peroxide (H₂O₂) with benzene (C₆H₆). Co-deposition experiments with H₂O₂ and C₆H₆ were performed at 20 K using argon as the matrix gas. New infrared peaks attributable to the H₂O₂-C₆H₆ complex were observed near the O-H stretching vibrations and the OH bending vibrations of the H₂O₂ monomer and near the hydrogen out-of-plane bending vibration of the C₆H₆ monomer. The initial identification of the newly observed infrared peaks to those of a H₂O₂-C₆H₆ complex was established by performing several concentration studies in which the sample-to-matrix ratios of the monomers were varied between 1:100 to 1:1600, by comparing the resulting co-deposition spectra with the spectra of the individual monomers, and by matrix annealing experiments (30 – 35 K). Co-deposition experiments using isotopically labeled hydrogen peroxide (D₂O₂ and HDO₂) and benzene (C₆D₆) in argon were also performed and the analogous peaks for the isotopically labelled complexes were observed. A series of co-deposition experiments with H₂O₂ and C₆H₆ was also performed using nitrogen as the matrix gas. Quantum chemical calculations were performed for the H₂O₂-C₆H₆ complex at the MP2/aug-cc-pVDZ and M06-2X/aug-cc-pVDZ levels of theory in order to obtain optimized complex geometries and predicted vibrational frequencies of the complex, which were compared to the experimental infrared spectra.

Weakly-bound complexes containing aromatic species have been the subject of study for many years. Here, a study of the weakly-bound complexes of thiophene () with water will be presented. In this study, matrix isolation FTIR and computational methods were used to examine stable 1:1 complexes of thiophene : water (Tp:). Multiple density functional theories along with MP2 calculations were used to find four stable geometries. Two geometries can be described by interaction, one by interaction, and one by interaction. These geometries were found to be within 10 kJ/mol of each other by all computational methods. Matrix isolation FTIR experiments identified several peaks that were not associated with isolated water or thiophene, implying the bands are due to weakly-bound complexes of the two. In addition to normal water, and HDO complexes with thiophene were also observed. Possible interpretations of the experimental and computational results will be presented. Comparisons to the structure of furan () : waterLockwood, S. P.; Fuller, T. G.; and Newby, J. J. J. Phys. Chem. A 2018, 122, 36, 7160-7170ill also be discussed.

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Lockwood, S. P.; Fuller, T. G.; and Newby, J. J. J. Phys. Chem. A 2018, 122, 36, 7160-7170w

The clustering of protonated ammonia clusters, a known interstellar ion, are studied with infrared photodissociation spectroscopy in the region of 4700 to 7200 cm⁻¹. H⁺(NH₃)_n clusters up to n=8 are produced using a pulsed electrical discharge in a supersonic expansion. Mass-selected ions are investigated using tunable infrared laser photodissociation in the turning region of a reflectron time of flight mass spectrometer. Clusters of protonated ammonia are probed through the dissociative elimination of an ammonia. The spectra gathered were assigned by comparing to B2PLYP/def2-TZVP computations. Two bands are consistently observed for the studied protonated ammonia clusters. A band at around 5000 cm⁻¹ is attributed to a combination of the N-H stretching and bending modes. Another band at around 6500 cm⁻¹ is assigned to either an overtone or a combination of the N-H stretching modes.