Acid dissociation reactions are at the heart of chemistry. These reactions are well understood at the macroscopic level. However, a microscopic level understanding is still in the early stages of development. Questions such as ‘how many H₂O molecules are needed to dissociate one HCl molecule?’ have been posed and explored both theoretically and experimentally.¹⁻⁵ Most of the theoretical calculations predict that four H₂O molecules are sufficient to dissociate one HCl molecule, resulting in the formation of a solvent separated H₃O⁺(H₂O)₃Cl⁻ cluster.¹⁻³ IR spectroscopy in helium nanodroplets has earlier been used to study this dissociation process.³⁻⁵ However, these studies were carried out in the region of O-H and H-Cl stretch, which is dominated by the spectral features of undissociated (HCl)_m-(H₂O)_n clusters. This contributed to the ambiguity in assigning the spectral features arising from the dissociated cluster.^4,5 Recent predictions from Bowman’s group, suggest the presence of a broad spectral feature (1300-1360 cm⁻¹) for the H₃O⁺(H₂O)₃Cl⁻ cluster, corresponding to the umbrella motion of H₃O⁺ moiety.⁶ This region is expected to be free from the spectral features due to the undissociated clusters. In conjunction with the FELIX laboratory, we have performed experiments on the (HCl)_m(H₂O)_n (m=1-2, n ≥ 4) clusters, aggregated in helium nanodroplets, in the 900-1700 cm⁻¹region. Mass selective measurements on these clusters revealed the presence of a weak-broad feature which spans between 1000-1450 cm⁻¹and depends on both HCl as well as H₂O concentration. Measurements are in progress for the different deuterated species. The details will be presented in the talk.
References: 1) C.T. Lee et al., J. Chem. Phys., 104, 7081 (1996). 2) H. Forbert et al., J. Am. Chem. Soc., 133, 4062 (2011). 3) A. Gutberlet et al., Science, 324, 1545 (2009). 4) S. D. Flynn et al., J. Phys. Chem. Lett., 1, 2233 (2010). 5) M. Letzner et al., J. Chem. Phys., 139, 154304 (2013). 6) J. M. Bowman et al., Phys. Chem. Chem. Phys., 17, 6222 (2015).

Anethole [(E)-1-methoxy-4-(1-propenyl)benzene] is a natural product molecule that is commonly recognized as the flavor component of anise, fennel, and licorice. Previously, we reported the jet-cooled, laser-induced fluorescence (LIF) and single vibronic level fluorescence (SVLF) spectra of anethole.J. Phys. Chem. A, 2013, 117 (48), 12831–12841n this work, several weak bands were observed and were tentatively assigned as van der Waals clusters of anethole with water. We have since confirmed this assignment and have conducted a more detailed study to determine the geometry of these clusters. Results from LIF, SVLF, and matrix isolation FTIRNewly built system at Hobart and William Smith Collegespectroscopy, as well as computational results will be presented in this talk. J. Phys. Chem. A, 2013, 117 (48), 12831–12841I Newly built system at Hobart and William Smith Collegess

The reductive conversion of CO₂ into industrial products (e.g., oxalic acid, formic acid, and methanol) can occur via aqueous CO₂⁻ as a transient intermediate. While the formation, structure and reaction pathways of this radical anion have been modelled for decades using various spectroscopic and theoretical approaches, we present here, for the first time, a vibrational spectroscopic investigation in liquid water, using pulse radiolysis time-resolved resonance Raman spectroscopy for its preparation and observation. Excitation of the radical in resonance with its 235 nm absorption displays a transient Raman band at 1298 cm⁻¹, attributed to the symmetric CO stretch, which is at   45 cm⁻¹higher frequency than in inert matrices. Isotopic substitution at C (¹³CO₂⁻) shifts the frequency downwards by 22 cm⁻¹which confirms its origin and the assignment. A Raman band of moderate intensity compared to the stronger 1298 cm⁻¹band also appears at 742 cm⁻¹, and is assignable to the OCO bending mode. A reasonable resonance enhancement of this mode is possible only in a bent CO₂⁻(C_2v/C_s) geometry. These resonance Raman features suggest a strong solute-solvent interaction, the water molecules acting as constituents of the radical structure, rather than exerting a minor solvent perturbation. However, there is no evidence of the non-equivalence (C_s) of the two CO bonds. A surprising resonance Raman feature is the lack of overtones of the symmetric CO stretch, which we interpret due to the detachment of the electron from the CO₂⁻ moiety towards the solvation shell. Electron detachment occurs at the energies of 0.28⁺/₋0.03 eV or higher with respect to the zero point energy of the ground electronic state. The issue of acid-base equilibrium of the radical which has been in contention for decades, as reflected in a wide variation in the reported pK_a (-0.2 to 3.9), has been resolved. A value of 3.4⁺/₋0.2 measured in this work is consistent with the vibrational properties, bond structure and charge distribution in aqueous CO₂⁻.

Hydrogen bonded complexes of phenylacetylene (PhAc) and HCl were studied using matrix isolation infrared spectroscopy and ab initio computations. An H…π complex was observed in our experiments, which was indicated to be the global minimum by our computations. In this complex, HCl serves as the proton donor to the acetylenic π cloud of PhAc. Computations also located two other minima on the PhAc-HCl potential surface. One was an H…π complex where the proton of HCl interacts with the π cloud of the phenyl ring, which was nearly isoenergetic with the global minimum. The other was an n-σ complex, where the acetylenic hydrogen in PhAc interacted with the chlorine of HCl. The phenylacetylene-HCl system was theoretically investigated, employing MP2 and M06-2X methods, with 6-311++G(d,p) and aug/cc-pVDZ basis sets. AIM, EDA and NBO analysis were also performed to explore the nature, physical origin and the strength of the noncovalent interactions. Experiments with phenylacetylene deuterated at the acetylenic hydrogen (PhAcD) were also performed, to confirm the above observation, through the isotopic effect. This work is part of a study of the hydrogen bonded interactions of phenylacetylene with various precursors, which provide an interesting interaction landscape ranging from a strong n-σ to a strong H-π interaction. As it turns out, HCl is at one end of this range, displaying a strong H-π interaction. While this presentation will give the details of the phenylacetylene-HCl complex, it will also summarize the landscape mentioned above, putting the present study in perspective.

References: 1. M. Majumder, B. K. Mishra, N. Sathyamurthy Chem. Phys. Lett. 2013,557,59-65
2. K. Sundararajan, K.S. Viswanathan, A.D. Kulkarni and S.R. Gadre. J. Mol. Str. 2002,613,209-222.

We identify new noble-gas compounds in solid matrices using IR spectroscopy. The compounds under study belong to two types: HNgY and YNgY’ where Ng is a noble-gas atom and Y and Y’ are electronegative fragments. The experimental assignments are supported by ab initio calculations at the MP2(full) and CCSD(T) levels of theory with the def2-TZVPPD basis set. We have prepared and characterized two new HNgY compounds (noble-gas hydrides): HKrCCCl in a Kr matrix and HXeCCCl in a Xe matrix.I The synthesis of these compounds includes two steps: UV photolysis of HCCCl in a noble-gas matrix to form the H + CCCl fragments and annealing of the matrix to mobilize H atoms and to promote the H + Ng + CCCl = HNgCCCl reaction. An interesting observation in the experiments on HXeCCCl in a Xe matrix is the temperature-induced transformation of the three H–Xe stretching bands. This observation is explained by temperature-induced changes of local matrix morphology around the embedded HXeCCCl molecule. In these experiments, we have also obtained the IR spectrum of the CCCl radical, which is produced by photodecomposition of HCCCl. We have identified three new YNgY’ compounds (fluorinated noble-gas cyanides): FKrCN in a Kr matrix and FXeCN and FXeNC in a Xe matrix.II These molecule are formed by photolysis of FCN in a noble-gas matrix due to locality of this process. The amount of these molecules increases upon thermal mobilization of the F atoms in the photolyzed matrix featuring the F + Ng + CN reaction.

EPR lineshape simulations of CH₃/SiO₂ clathrates reveal the motional conditions of the CH₃ radical up to the unusual regime of its stability, the high temperature diffusional regime. This was obvious by the isotropic magnetic interaction at the highest experimental temperatures over 140 K. Special motional and thermodynamics conditions for methyl radical may however prevail for the CH₃/SiO₂ clathrates system due to the limited space of the host voids, compared to solid gas isolation. The lowest temperature in the experiment was 4.1 K, while the highest one was 300 K. The EPR parameters of the radical revealed non-monotonic temperature dependence. The extremely wide temperature range of the radical stability may be attributed to the solidity of the clathrate voids and the small diameter of their channels that do not allow molecular collisions between the radical species. At the lowest sample temperatures, a portion of the radicals stopped to rotate thus indicating their attachment to specific matrix sites with large radical-host interaction. The unusual increase of the width of the CH₃/SiO₂ clathrate spectra with the temperature at high sample temperatures indicates resemblance to the spin-rotation interaction relaxation mechanism known only in the case of small species in non-viscous fluids, and is contrasted to the normal difussional decrease of the width in the CH₃ hosted in a series of solid. The effect was explained by adopting extremely frequent radical collisions with the clathrate void walls leading to repeated angular momentum alterations, a kind of “reorientation”.Yu. A. D. acknowledges support by the Russian Foundation for Basic Research (RFBR), research project 16-02-00127a.html:<hr /><h3>Footnotes: Yu. A. D. acknowledges support by the Russian Foundation for Basic Research (RFBR), research project 16-02-00127a.

Ethanol can exist in two conformers, one in which the OH group is trans to the methyl group (trans-ethanol) and the other in which the OH group is gauche to the methyl group (gauche-ethanol). Matrix isolation infrared spectra of ethanol deposited in 20 K argon matrices display distinct infrared peaks that can be assigned to the trans-ethanol and gauche-ethanol conformers, particularly with the O-H stretching vibrations.Barnes, A. J.; Hallam, H. E. Trans. Faraday Soc., 1970, 66, 1932-1940.iven this, matrix isolation experiments were performed in which ethanol (C₂H₅OH) and benzene (C₆H₆) were co-deposited in argon matrices at 20 K in order to determine if conformer specific ethanol complexes with benzene could be observed in the infrared spectra. New infrared peaks that can be attributed to the trans-ethanol and gauche-ethanol complexes with benzene have been observed near the O-H stretching vibrations of ethanol. The initial identification of the new infrared peaks as being due to the ethanol-benzene complexes was established by performing a concentration study (1:200 to 1:1600 S/M ratios), by comparing the co-deposition spectra with the spectra of the individual monomers, by matrix annealing experiments (35 K), and by performing experiments using isotopically labeled ethanol (C₂D₅OD) and benzene (C₆D₆). Quantum chemical calculations were also performed for the C₂H₅OH-C₆H₆ complexes using density functional theory (B3LYP) and ab initio (MP2) methods. Stable minima were found for the both the trans-ethanol and gauche-ethanol complexes with benzene at both levels of theory and were predicted to have similar interaction energies. Both complexes can be characterized as H-π complexes, in which the ethanol is above the benzene ring with the hydroxyl hydrogen interacting with the π cloud of the ring. The theoretical O-H stretching frequencies for the complexes were predicted to be shifted from the monomer frequencies and from each other and these results were used to make the conformer specific infrared peak assignments.

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Barnes, A. J.; Hallam, H. E. Trans. Faraday Soc., 1970, 66, 1932-1940.G

The separated CO₂ dimer anion, (CO₂)(CO₂⁻), is observed by FTIR spectroscopy in matrix isolation experiments at 1652 cm⁻¹ upon deposition of high energy argon ions into an argon matrix doped with 0.5% CO₂. It has previously been reported by Andrews that upon annealing the matrix to 25K, the separated species converts to an oxalate-like C₂O₄⁻ species which appears at 1856 cm⁻¹.^a We have observed that subsequently holding the matrix at 10K caused the C₂O₄⁻ species to fully convert back to (CO₂)(CO₂⁻). Upon further investigation, we determined that the two species reversibly interconvert between 19K and 23K, suggesting the species are in thermodynamic equilibrium. The associated van’t Hoff plot has a linear trend and indicates an endothermic reaction driven by a large increase in entropy. An analogous experiment in a krypton matrix was performed, and the equilibrium was found to occur between 26K and 31K. Interestingly, analysis revealed the reaction in krypton is more endothermic, but has nearly the same entropy value as was observed in the argon experiment. ^aZhou, M.; Andrews, L.; J. Chem. Phys. 110, 2414 (1999).

A focus of the research in our group has been to develop improved methods for ion delivery in matrix isolation experiments. We have previously reported a method to co-deposit low energy, mass selected metal anions and a rare gas counter cation.^a A modification allowing for mass selection of both the anion and cation will be discussed. Results from preliminary experiments of mass selected, low energy Cu⁻ and SF₅⁺ will also be highlighted. To our knowledge, these experiments are the first time two mass selected beams of ions have been simultaneously deposited into a cryogenic matrix. Co-deposition of the ions into an argon matrix doped with 0.02% CO at 20K resulted in the observation of bands assigned to SF₅⁺ and anionic copper carbonyl complexes, Cu(CO)_n⁻ (n=1-3). Upon irradiation of the matrix with a narrow band, blue LED, the copper carbonyl complexes are converted to the neutral analogues, while the fate of the photodetached electrons can be directly tracked, as a decrease of the SF₅⁺ band and a growth of the neutral SF₅ band are observed. ^aLudwig, R. M.; Moore, D. T.; J. Chem. Phys. 139, 244202 (2013).

The absorption spectrum of the ν₃ (C-F stretching) mode of CH₃F in solid para-H₂ by FTIR showed a series of equal interval peaksK. Yoshioka and D. T. Anderson, J. Chem. Phys. 119 (2003) 4731-4742 Their interpretation was that the n-th peak of this series was due to CH₃F-(ortho-H₂)_n clusters which were formed CH₃F and n’s ortho-H₂ in first nearest neighbor sites of the para-H₂ crystal with hcp structure. In order to understand this system in more detail, we have studied these peaks, especially n = 0 – 3 corresponding to 1037 - 1041 cm⁻¹, by using high-resolution and high-sensitive infrared quantum cascade laser (QCL) spectroscopy. Before now, we have observed photochromic phenomena of these peaks by taking an advantage of the high brightness of the laserA. R. W. McKellar, A. Mizoguchi, and H. Kanamori, Phys. Chem. Chem. Phys. 13 (2011) 11587-11589 However, it has not been revealed what kind of mechanism is undergoing in these processes. In order to solve this problem we introduced two cw-IR QCLs for pump and prove experiment. While the pumping laser is breaching a certain peak with high power, the probing laser is monitoring the increase of other peaks by rapid scan method. The time resolution of this spectroscopy is 5 msec. The new precise kinetic information will help us to understand the molecular interaction in solid para-H₂.

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K. Yoshioka and D. T. Anderson, J. Chem. Phys. 119 (2003) 4731-4742. A. R. W. McKellar, A. Mizoguchi, and H. Kanamori, Phys. Chem. Chem. Phys. 13 (2011) 11587-11589.

In this study, we present Fourier transform infrared spectroscopic studies of the 193 nm photochemistry of nitric oxide (NO) isolated in a parahydrogen (pH₂) matrix over the 1.7 to 4.3 K temperature range. Back in 2003 Fushitani and MomoseM. Fushitani, T. Momose, Low Temp. Phys. 29, 985-988 (2003).howed that hydrogen atoms (H atoms) are produced as by-products of the 193 nm photo-initiated reactions of NO trapped in solid pH₂. We recently publishedM. Ruzi, D.T. Anderson, J. Phys. Chem. A 119, 12270-12283 (2015). further study on the same NO/pH₂ system where we showed that H atom reactions with NO produce both HNO and NOH even though the reaction that forms HNO is barrierless and the reaction that forms NOH has a sizeable barrier. Further, we measured the reaction kinetics at 1.8 K and 4.3 K and showed the rate constants follow an Arrhenius-behavior with a small activation energy (E_a=2.39(1) cm⁻¹). In the present studies we are continuing this work using a ¹⁵NO enriched sample and are focusing on how we can adjust the experimental conditions to increase the yield of both the HNO/NOH reaction products. We are also performing kinetic experiments at more than just two temperatures to better characterize the temperature dependence of the extracted rate constants. We are conducting these additional experiments to benchmark the reaction kinetics for the H + NO reaction in solid pH₂ to better understand what factors influence the rates of these low temperature chemical reactions. M. Fushitani, T. Momose, Low Temp. Phys. 29, 985-988 (2003).s M. Ruzi, D.T. Anderson, J. Phys. Chem. A 119, 12270-12283 (2015).a

In situ photolysis of precursor molecules trapped in a solid parahydrogen matrix has been successfully used in our group to study H atom reactions with other species at temperatures in the range of 1.6 to 4.3 K. At these temperatures, H atoms are known to continuously move through the solid by the H + H₂ → H₂ + H tunneling exchange reaction. We recently studied the reaction of H atoms with ¹⁵N₂O and in the preliminary communication of this work,F. M. Mutunga, S. E. Follett, D. T. Anderson, J. Chem. Phys. 139, 151104 (2013).e reported a very strange non-Arrhenius temperature dependence to the reaction; the reaction only occurs below 2.4 K and not at higher temperatures. This talk will present our subsequent work on the high-resolution infrared spectroscopy of ¹⁵N₂O molecules trapped in solid parahydrogen with a focus on the ν₁ + ν₃ and 2ν₁ vibrational bands. For both these vibrational bands we observe multiple peaks and the relative intensities of the observed peaks change with temperature over the measured range similar to the temperature dependence of the ν₃ fundamental reported earlier by Lorenz and Anderson.B. D. Lorenz and D. T. Anderson, J. Chem. Phys. 126, 184506 (2007).he temperature dependent changes in intensity imply that there are at least two trapping sites which could potentially explain the observed temperature dependence to the H + ¹⁵N₂O reaction.

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F. M. Mutunga, S. E. Follett, D. T. Anderson, J. Chem. Phys. 139, 151104 (2013).w B. D. Lorenz and D. T. Anderson, J. Chem. Phys. 126, 184506 (2007).T

The linear tetratomic organic molecule acetylene, HCCH, has been studied extensively throughout the past century via numerous spectroscopic experiments, exploiting wavelengths across the electromagnetic spectrum. Both the mono- and di-deutero acetylene isotopologues have also been widely studied, namely HCCD and DCCD. In this presentation, I will present the Fourier transform infrared (FTIR) spectroscopy of DCCD in solid parahydrogen (pH₂) in the low-temperature regime (1.5-5.0 K). We intend to perform UV photochemical studies on DCCD doped solid pH₂ and, therefore, the infrared spectroscopy must be characterized prior. The FTIR spectrum of DCCD isolated in solid pH₂ exhibits rich fine structure in the ν₃ asymmetric C-D stretch region. Some of the observed peaks may arise from the formation of weakly bound acetylene dimers, or potentially even larger clusters. We can test this hypothesis by varying the DCCD concentration in separate experiments and temperature cycling the matrix to look for irreversible cluster growth. In preliminary experiments we observe trace amounts of the lighter isotopologues (HCCD and HCCH) and so these species can also cluster with DCCD, adding to the complexity of the spectra. We remark that ortho-hydrogen clustering to DCCD may also be occurring and we have ways to check that as well. In order to make better sense of the FTIR spectrum of DCCD doped pH₂, a comparison with the simulated low temperature gas-phase spectrum will also be presented. This will allow us to address issues related to the extent of the rotational motion of DCCD in solid pH₂. A liquid helium bath cryostat is used to grow and maintain the DCCD doped pH₂ crystals for spectroscopic characterization. Helium is a non-renewable resource and in recent years the Anderson group has been building a helium recovery system. This Helium Recovery Initiative (HRI) will be discussed in an effort to describe how we implemented this new experimental system in our laboratory and to point out the major challenges we faced. One of the main goals of the HRI is to promote sustainable helium use, permitting smaller cryogenics laboratories to continue conducting research with liquid helium.