(n,m) = (1,2).   CO₂-Ar₂ has previously been studied in the microwaveY. Xu, W. Jäger, and M.C.L. Gerry, J. Mol. Spectrosc. 157, 132 (1993).nd infrared.J.M. Sperhac, M.J. Weida, and D.J. Nesbitt, J. Chem. Phys. 104 2202 (1996).ts structure has two Ar atoms occupying equivalent positions around the 'equator' of the CO₂, giving C_2v symmetry. Here we report observation of analogous infrared spectra of CO₂-Ne₂ and CO₂-Xe₂. Meanwhile, for CO₂-Ar₂ we observe a new a-type combination band giving an intermolecular bending frequency of 32.2 cm⁻¹. Unlike the fundamental band, the combination band is free of interference from stronger CO₂-Ar transitions. Also, we observe CO₂-Ar₂ in the CO₂ (01¹1) - (01¹0) hot band region, as well as weak fundamental band spectra of the mixed trimers CO₂-Rg-He, with Rg = Ne, Ar, Xe. (n,m) = (1,3).   An interesting band near 2345.2 cm⁻¹ is assigned to CO₂-Xe₃, whose structure appears to have C_s symmetry containing a xenon trimer (near equilateral triangle) and a CO₂ positioned so that two of the Xe atoms are in equivalent near equatorial positions. (n,m) = (2,1).   We have assigned spectra of new trimers, (CO₂)₂-Rg. The Xe-containing species was noticed first, and this led us to identify weaker spectra with Ar and (even weaker) Ne. Their structures resemble having a CO₂ dimer (planar slipped parallel) with the Rg atom located 'above' the dimer plane on (or close to) the dimer symmetry axis, analogous to (CO₂)₂-CO.A.J. Barclay, A.R.W. McKellar, and N. Moazzen-Ahmadi, Chem. Phys. Lett. 677, 127 (2017).n the future, it should be possible to assign the various Kr clusters and to optimize each cluster by varying the expansion gas mixtures. Y. Xu, W. Jäger, and M.C.L. Gerry, J. Mol. Spectrosc. 157, 132 (1993).a J.M. Sperhac, M.J. Weida, and D.J. Nesbitt, J. Chem. Phys. 104 2202 (1996).I A.J. Barclay, A.R.W. McKellar, and N. Moazzen-Ahmadi, Chem. Phys. Lett. 677, 127 (2017).I

Spatial overlap of two non-bonding orbitals of ionized and neutral molecules can result in formation of a hemibond (two-center three-electron (2c3e) bond). Though hemibond formation between water and rare gas atom has been theoretically predicted, no definite experimental evidence has been reported. In the present study, we perform infrared spectroscopy of [H₂O-(Kr)_n]⁺ (n=1-3) clusters in the gas phase. Comparison of the observed spectral features in the OH stretch region with the ab initio anharmonic vibrational simulations demonstrates the hemibond formation between water and Kr in all the observed cluster sizes.

Iron is the most abundant metal on Earth and is involved in many critically important processes. Iron is commonly found in nature in its mineral forms, and in aqueous solutions as a complex with other soluble salts where hydration also plays a key role in its subsequent speciation. Aqueous interfaces are the gateway to many natural and biological reactions, including those that involve soluble Fe(III). Yet, interfacial iron complexation and surface prevalence are not well understood, especially under the inherently acidic conditions of \chem{FeCl_3} solutions. In this study, we investigate interfacial Fe(III) species using second harmonic generation (SHG) combined with surface tension and UV/visible absorption. Surface selective techniques such as SHG have been widely applied to unveil the unique properties of substances within the air-aqueous interface. Here, we observe two different interfacial regions with increasing concentration marked by two distinctly different SHG electric-field (E-field) trends. Below 2.0 mol/kg water aqueous \chem{FeCl_3}, nonresonant SHG behavior is observed, similar to the E-field generated from the aqueous sodium iodide surface, but much larger in magnitude than aqueous NaCl and NaBr solution surfaces. Above 2.0 mol/kg water, a significant increase in the SHG slope is observed, much larger than that of the aqueous sodium halide electrolyte surfaces. Through further evaluation of symmetry and resonant behavior, we determine the existence of the neutral \chem{[FeCl_3](H_2O)_3]} complex.

Anisole has two prominent hydrogen bonding sites, namely oxygen and the π-electrons of the phenyl ring. Earlier studies on anisole-water^1,2 and anisole-methanol³ complexes show that in both cases the interaction with the oxygen atom is preferred and complex formation takes place via OH-O hydrogen bonding, where water/methanol acts as hydrogen bond donor. We have studied anisole-methanol complexes in superfluid helium droplets, using high-resolution infrared spectroscopy.⁴ Several bands corresponding to (anisole)_m-(methanol)_n complexes (where m=1,2 and n=1) were observed. The size of the clusters corresponding to the observed bands was determined by recording the band intensity as a function of the partial pressures of the constituent molecules, resulting in so-called pickup curves.⁵ A comparison of the observed spectra with the calculated spectra, at MP2/6-311++G (d,p) level of theory, suggests the formation of four different conformers of the anisole-methanol dimer in helium droplets. Among them, the two structures with the largest binding energies are predominantly stabilized via OH-O hydrogen bonds and the other two via OH-π hydrogen bonds. References: 1. B. Reimann, K. Buchhold, H.-D. Barth, B. Brutschy, P. T arakeshwar, and Kwang S. Kim, J. Chem. Phys., 2002, 117, 8805. 2. M. Becucci, G. Pietraperzia, M. Pasquini, G. Piani, A. Zoppi, R. Chelli, E. Castellucci and W. Demtroeder, J. Chem. Phys., 2004, 120, 5601. 3. M. Heger, J. Altno, A. Poblotzki and M. A. Suhm, Phys. Chem. Chem. Phys., 2015, 17, 13045. 4. Tarun Kumar Roy, Devendra Mani, Gerhard Schwaab, Martina Havenith, Phys. Chem. Chem. Phys., 2020, 22, 22408. 5. M. Lewerenz, B. Schilling and J. P. Toennies, J. Chem. Phys., 1995, 102, 8191.

To date, carbon-rich clusters harboring heavy elements have received little attention from both experiment and quantum chemistry. Recent high-resolution infrared survey scans of laser ablation products from carbon-tellurium targets in the 5μm wavelength regime show two vibration-rotation bands not observed previously. On the basis of comparison with results from density-functional theory and high-level quantum-chemical calculations performed at the CCSD(T) level of theory these bands are attributed to two new linear chains, C₃Te and TeC₃Te.

One of the largest unknowns in the understanding of aerosol particles is the structure and growth process that drives new particle formation, particularly from a molecular point of view. These processes are dictated by the underlying interplay of hydrogen-bonding interactions of the organic molecules with water and water with itself. The presence of amine groups may further accelerate new particle formation; thus we model the vibrational spectra of clusters of several heterocyclic molecules complexed with water and ammonia. We model the OH and NH stretching regions of the clusters’ IR spectra through a suite of approaches that have favorable computational scaling and cost compared to standard anharmonic approaches. This acceleration allows us to consider the numerous cluster candidates and provide assignments. Finally, the wealth of spectral data (both theoretical and experimental) allows us to test the performance of data-driven spectroscopic models.

A progression of strong bands in the 900-2200 cm⁻¹  region are observed in the infrared laser photodissociation spectrum of Ar₃H⁺.D.C. McDonald II, D.T. Mauney, D. Leicht, J.H. Marks, J.A. Tan, J.-L. Kuo, and M.A. Duncan, J. Chem. Phys. 145, 231101 (2016).n this talk, computational studies were conducted to examine the structures, binding energies, and infrared spectra for Ar_nH⁺ (n=2-3). We found that the minimum structure for Ar₂H⁺ is linear and centrosymmetric, while Ar₃H⁺ can be either T-shaped or linear.J.A. Tan and J.-L. Kuo, J. Phys. Chem. A 124, 7726–7734 (2020). series of potential energy surfaces at the CCSD(T)/aug-cc-pVTZ level of theory and basis set was constructed and used for the calculation of anharmonic spectrum using discrete variable representation (DVR).J.C. Light, I.P. Hamilton, and J. V. Lill, J. Chem. Phys. 82, 1400 (1985).nharmonic theory can reproduce the observed strong bands, which were associated with the core Ar₂H⁺ ion. These bands are assigned as combination bands of the asymmetric Ar-H⁺ stretch with multiple quanta of the symmetric Ar-H⁺ stretch. D.C. McDonald II, D.T. Mauney, D. Leicht, J.H. Marks, J.A. Tan, J.-L. Kuo, and M.A. Duncan, J. Chem. Phys. 145, 231101 (2016).I J.A. Tan and J.-L. Kuo, J. Phys. Chem. A 124, 7726–7734 (2020).A J.C. Light, I.P. Hamilton, and J. V. Lill, J. Chem. Phys. 82, 1400 (1985).A

The infrared spectrum of CO₂-Xe is studied in the region of the carbon dioxide ν₃ fundamental vibration (near 2350 cm⁻¹), using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. We generally think of Xe or Kr isotope effects to be mostly unresolved for infrared spectra of weakly-bound van der Waals complexes. But here we model the Xe isotope dependence of the spectrum by scaling the vibrational and rotational parameters with the help of previous microwave data,M. Iida, Y. Ohshima, and Y. Endo, J. Phys. Chem. 97, 357 (1993).sing features built into PGOPHER.PGOPHER, A Program for Simulating Rotational, Vibrational and Electronic Spectra, C.M. Western, University of Bristol, http://pgopher.chm.bris.ac.ukhis model provides a very good simulation of the observed broadening and (partial) splitting of transitions in the fundamental band. More importantly, it is essential for understanding the intermolecular bending combination band, where many transitions are completely split by isotope effects. The combination band is influenced by a significant bend-stretch Coriolis interaction and by the relatively large Xe isotope dependence of the intermolecular stretch frequency. It turns out that K_a = 1 levels of the stretch lie above K_a = 2 levels of the bend for CO₂-¹²⁹Xe, but below them for CO₂-¹³⁶Xe. This greatly enhances the Xe isotope dependence of the Coriolis interaction. The weak CO₂-Xe spectrum corresponding to the (01¹1) - (01¹0) hot band of CO₂ is also detected and analyzed, providing a measurement of the symmetry breaking of the CO₂ ν₂ bending mode induced by the nearby Xe atom. This in-plane / out-of-plane splitting is determined to be 2.14 cm⁻¹, with the out-of-plane mode lying higher in energy.

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Footnotes:

M. Iida, Y. Ohshima, and Y. Endo, J. Phys. Chem. 97, 357 (1993).u PGOPHER, A Program for Simulating Rotational, Vibrational and Electronic Spectra, C.M. Western, University of Bristol, http://pgopher.chm.bris.ac.ukT

Interstellar dust contains to a large extent μm-sized silicate particles. The origin and evolutionary processes of these are still poorly understood. Only one possible precursor, molecular SiO in a circumstellar disk, has been observed so far.^[1] We present experimental data and quantum chemical calculations on the absorption and dissociation properties of small Si_nO_m⁺ clusters (n=10−12, m=1−2) that are potential intermediates between the circumstellar SiO diatomic molecule and silicate grains observed in the interstellar medium. The spectra are the first optical absorption spectra of Si_nO_m⁺ cations and obtained by photodissociation of mass-selected ions generated in a laser desorption source.^[2] We compare our experimental results to TD-DFT calculations and discuss them in an astrophysical context.
Literature: [1] R. Wilson et al., Astrophys. J., 1971, 167, L97. [2] M. Förstel et al., Rev. Sci. Instrum., 2017, 88, 123110.

We previously observed the spectrum of (CO₂)₂-CO in the region of the CO fundamental band (2150 cm⁻¹).A.J. Barclay, A.R.W. McKellar, and N. Moazzen-Ahmadi, Chemical Physics Letters 677, 127 (2017).ts structure resembles that of a CO₂ dimer (planar slipped-parallel) with a CO monomer aligned along the dimer C₂ symmetry axis in a C-bonded configuration, giving a trimer with C₂ symmetry. We have now observed three bands of the same species in the CO₂ ν₃ region. Two of these bands are fundamentals, one a/c-type and the other b-type. The presence of this b-type band establishes that the CO₂ dimer subunit within the trimer is actually not planar. The third band is a b-type combination band near 2376 cm⁻¹. A new c-type fundamental near 2349.5 cm⁻¹and an a-type combination band near 2365.2 cm⁻¹are assigned to CO₂-(CO)₂. The structure has two C-bonded CO monomers in equivalent positions around the CO₂ 'equator', giving a C_2v geometry analogous to that of CO₂-Ar₂. A similar fundamental is observed for CO₂-(N₂)₂ near 2350.0 cm⁻¹. The weak parallel band of a symmetric or near-symmetric rotor near 2349.2 cm⁻¹is assigned to CO₂-(CO)₃, together with an analogous band of CO₂-(N₂)₃ near 2349.8 cm⁻¹. We think that these tetramers are accidental symmetric rotors having C_s symmetry. They are obtained by taking the C_2v trimers from the previous paragraph and adding a third CO or N₂ to the 'side' of the first two, in the plane bisecting them.

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Footnotes:

A.J. Barclay, A.R.W. McKellar, and N. Moazzen-Ahmadi, Chemical Physics Letters 677, 127 (2017).I

The infrared spectrum of CO₂-Kr in the region of the carbon dioxide ν₃ fundamental vibration (near 2350 cm⁻¹) was first studied by Randall et al.R.W. Randall. M.A. Walsh, and B.J. Howard, Faraday Discuss. Chem. Soc. 85, 13 (1988).ere we reexamine this spectrum, using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion of a dilute mixture of CO₂ and Kr in helium. The bending combination band, which is observed near 2378 cm⁻¹, yields an intermolecular bending frequency of 29.43 cm⁻¹, in fairly good agreement with a theoretical prediction of 30.02 cm⁻¹ by Chen et al.R. Chen, H. Zhu, and D. Xie, Chem. Phys. Lett. 511, 229 (2011).he spectrum of CO₂-Kr in the region of the CO₂ (01¹1) - (01¹0) hot band is also observed, following on our recent study of this transition in CO₂-Ar.T.A. Gartner, A.J. Barclay, A.R.W. McKellar, and N. Moazzen-Ahmadi, Phys. Chem. Chem. Phys. 22, 21488 (2020).his gives a measurement of the symmetry breaking of the CO₂ ν₂ bending mode caused by the Kr atom. The out-of-plane mode turns out to be about 1.42 cm⁻¹ higher than the in-plane mode for CO₂-Kr, as compared to splittings of 0.06 cm⁻¹ for CO₂-Ne, 0.88 cm⁻¹ for CO₂-Ar, and 2.14 cm⁻¹ for CO₂-Xe. R.W. Randall. M.A. Walsh, and B.J. Howard, Faraday Discuss. Chem. Soc. 85, 13 (1988).H R. Chen, H. Zhu, and D. Xie, Chem. Phys. Lett. 511, 229 (2011).T T.A. Gartner, A.J. Barclay, A.R.W. McKellar, and N. Moazzen-Ahmadi, Phys. Chem. Chem. Phys. 22, 21488 (2020).T

The rovibrational spectra of N₂−D₂O and N₂−DOH were measured around the OD stretching region. A combination band involving the in-plane N₂ bend intermolecular vibration was also observed in the same frequency range. These bands were measured at the University of Calgary 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 fit to a series of independent asymmetric rotors. The rotational constants of the four tunneling components of N₂−D₂O were retrieved for the excited vibrational states. Small vibrational blue shifts of 0.6 cm⁻¹ and 1.8 cm⁻¹ compared to the D₂O monomer band origins were determined for the symmetric and asymmetric stretches, respectively. A two order of magnitude larger tunneling splittings is observed for the asymmetric OD stretching excitation compared to the symmetric one. This last finding indicate a significant change of the intermolecular dynamics due to the intramolecular asymmetric OD vibration.