We performed infrared predissociation spectroscopy of size-selected pentane-water cluster cations, [pentane-(H₂O)_n]⁺, n=1-3, generated through the vacuum-ultraviolet photoionization. In the infrared spectra of the di- and tri-hydrated clusters, there appear broad features which spread to the lower frequency region from 2800 cm⁻¹. These broad features are assigned to vibrations of a proton, which is transferred from CH of the pentane cation to the water molecules. These results indicate that the pentane cation has high proton donor ability. We will discuss these results based on theoretical conputations.

Isomer-specific resonant ion-dip infrared spectra are presented for benzene-(water)_n, 1-2-diphenoxyethane-(water)_n, and tricyclophane-(water)_n clusters. The IR spectra are modeled with a local mode Hamiltonian that was originally formulated for the analysis of benzene-(water)_n clusters with up to seven waters. The model accounts for stretch-bend Fermi coupling, which can complicate the IR spectra in the 3150-3300 cm⁻¹ region. When the water clusters interact with each of the solutes, the hydrogen bond lengths between the water molecules change in a characteristic way, reflecting the strength of the solute-water interaction. These structural effects are also reflected spectroscopically in the shifts of the local mode OH stretch frequencies. When diphenoxyethane is the solute, the water clusters distort more significantly than when bound to benzene. Tricyclophane's structure provides an aromatic-rich binding pocket for the water clusters. The local mode model is used to extract Hamiltonians for individual water molecules. These monomer Hamiltonians divide into groups based on their local H-bonding architecture, allowing for further classification of the wide variety of water environments encountered in this study.

Experimental studies have shown that features in the vibrational spectra of H₃O⁺ can be modulated not only by the type messengers, but also by the number of messengers. Recently, we compared the experimental H₃O⁺Ar_m, m=1-3 spectra with accurate theoretical simulations and obtain the peak position and absorption intensity by solving the quantum vibrational Schrodinger equation using the potential and dipole moment obtained ab initio methods.J-W Li, M. Morita, T. Takahashi and J-L Kuo, J. Phys. Chem. A, 119, 10887 (2015)n this work, we studied isotopolgues of this ionic cluster to glean into the details of the vibrational couplings manifested in the spectra region of 1500-3800 cmcm⁻¹.

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J-W Li, M. Morita, T. Takahashi and J-L Kuo, J. Phys. Chem. A, 119, 10887 (2015)I

Several monoterpenes and terpenoids are biogenic volatile organic compounds which are emitted in the atmosphere, where they react with OH, O₃ and NO_x etc. to give rise to several oxidation and degradation products.A. Calogirou, B.R. Larsen, and D. Kotzias, Atmospheric Environment, 33, 1423-1439, (1999).heir decomposition products are a major source of secondray organic aerosol (SOA).P. Paasonen et al., Nat. Geosci., 6, 438-442 (2013)pectroscopic information on these atmospheric species is still very scarce. The rotational spectrum of nopinone (C₉H₁₄O) one of the major oxidation products of β-pinene,D. Zhang and R. Zhang The Journal of Chemical Physics, 122, 114308, (2005).R. Winterhalter et al. Journal of Atmospheric Chemistry, 35, 165-197, (2000). and of its water complexes were recorded in a supersonic jet expansion with a Fourier transform microwave spectrometer over the range 2-20 GHz. The structure of the unique stable conformer of the nopinone was optimized using density functional theory and ab initio calculations. Signals from the parent species and from the ¹³C and ¹⁸O isotopomers were observed in natural abundance. A magnetic hyperfine structure associated with the pairs of hydrogen nuclei in the methylene groups was observed and modeled.
The structures of several conformers of the nopinone-water complexes with up to three molecules of water were optimized using density functional theory and ab initio calculations. The energetically most stable of calculated conformers were observed and anlyzed. The rotational and centrifugal distortion parameters were fitted to a Watson’s Hamiltonian in the A-reduction. The present work provides the first spectroscopic characterization of nopinone and its water complexes in the gas phase.

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A. Calogirou, B.R. Larsen, and D. Kotzias, Atmospheric Environment, 33, 1423-1439, (1999).T P. Paasonen et al., Nat. Geosci., 6, 438-442 (2013)S D. Zhang and R. Zhang The Journal of Chemical Physics, 122, 114308, (2005).

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Since they were first synthetized, crown ethers have been extensively used in organometallic chemistry due to their unparalleled binding selectivity with alkali metal cations. From a structural point of view, crown ethers are heterocycles containing oxygen and/or other heteroatoms, although the most common ones are formed from ethylene oxide unit. Crown ethers are conventionally seen as being hydrophilic inside and hydrophobic outside when the structures found for the metal cation complexes are considered. However, crown ethers are extremely flexible and in isolation may present a variety of stable conformationsF. Gámez, B. Martínez-Haya, S. Blanco,J. C. Lòpez and J. L. Alonso, Phys. Chem. Chem. Phys. 2014, 14 12912-12918o that their structure may be easily adapted in presence of a strong ligand as an alkali metal cation minimize the energy of the resulting complex. Water can be considered a soft ligand which interacts with crown ethers through moderate hydrogen bonds. It is thus interesting to investigate which conformers are selected by water to form complexes, the preferred interaction sites and the possible conformational changes due to the presence of one or more water molecules. Previous studies identified microsolvated crown ethers but in all cases with a chromophore group attached to the structure.V. A. Shubert, C.W. Müller and T. Zwier, J. Phys. Chem. A 2009, 113 8067-8079ere we present a broadband rotational spectroscopy study of microsolvated crown ethers produced in a pulsed molecular jet expansion. Several 1:1 and 1:2 crown ether:water aggregates are presented for 12-crown-4, 15-crown-5 and 18-crown-6. Unambiguous identification of the structures has been achieved using isotopic substitution within the water unit. The subtle changes induced in the structures of the crown ether monomer upon complexation and the hydrogen-bonding network that hold them together will be also discussed.

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F. Gámez, B. Martínez-Haya, S. Blanco,J. C. Lòpez and J. L. Alonso, Phys. Chem. Chem. Phys. 2014, 14 12912-12918s V. A. Shubert, C.W. Müller and T. Zwier, J. Phys. Chem. A 2009, 113 8067-8079H

Over the past few years, we have used H₂¹⁸O water substitution to determine the structures of water clusters by molecular rotational spectroscopy. In the case of the water hexamer, the energy difference between the cage and prism structures is calculated to be about 0.1 kcal/mol and this energy difference is of the order of the zero-point energy variation between the isomers. Using rotational spectroscopy we provided experimental evidence for three isomers, i.e, cage, prism and book and established their relative energy ordering.C. Pérez, et al, Science. 2012, 336 897-901n the special case of the prism hexamer, cluster dynamics causes measurable splitting in rotational transitions resulting from tunneling between discernible equivalent minima. Multiple isotopic substitution measurements involving all 64 possible isotopologues of the water hexamer prism (H₂¹⁸O)_n(H₂¹⁶O)_6−n were performed in order to identify the water molecules involved in the tunneling motion. The analysis of these tunneling-rotation spectra suggests that there are two distinct tunneling paths that involve concerted motion of two water molecules, implying a prototype scenario involving the breaking of two hydrogen bonds.J. O. Richardson et al, Science. 2016, in presshtml:<hr /><h3>Footnotes: C. Pérez, et al, Science. 2012, 336 897-901I J. O. Richardson et al, Science. 2016, in press

Using broadband rotational spectroscopy, we will present our results on the microsolvation of camphor (C₁₀H₁₆O) complexed with up to three water molecules.C. Pérez, A. Krin, A. L. Steber, J. C. López, Z. Kisiel, M. Schnell, J. Phys. Chem. Lett. 2016, 7 154-160.nambiguous assignment was achieved by performing multi H₂¹⁸O isotopic substitution of clustered water molecules. The observation of all possible mono- and multi-H₂¹⁸O insertions in the cluster structure yielded accurate structural information that is not otherwise achievable with single-substitution experiments. The observed clusters exhibit water chains starting with a strong hydrogen bond to the carbonyl group and terminated by a mainly van der Waals (dispersive) contact to one of the available sites at the monomer moiety. The effect of hydrogen bond cooperativity is noticeable, and will be also discussed.

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C. Pérez, A. Krin, A. L. Steber, J. C. López, Z. Kisiel, M. Schnell, J. Phys. Chem. Lett. 2016, 7 154-160.U

Mixtures of formic acid with methyl alcohol, with isopropyl alcohol, with tert-butyl alcohol, with dimethylether and with isopropylformiate have been supersonically expanded as pulsed jets. The obtained cool plumes have been analyzed by Fourier transform microwave spectroscopy. It has been possible to assign the rotational spectra of the 1:1 adducts of formic acid with tert-butyl alcohol, with dimethyl ether and with isopropylformiate. The conformational shapes and geometries of these adducts, as well as the topologies of their itermolecular hydrogen bonds will be presented. An explanation is given of the failure of the assignments of the rotational spectra of the adducts of formic acid with methyl alcohol and isopropyl alcohol.

The hydrogen bond donor/acceptor competition in mixed alcohol clusters remains a fundamental question in physical chemistry. Previous theoretical work on the prototype ethanol-methanol dimer has been inconclusive in predicting the energetically preferred structure. Here, we report the microwave spectrum of the ethanol-methanol dimer between 8-18 GHz, using a chirped pulse Fourier transform microwave spectrometer. With the aid of ab initio calculations, 36 transitions have been fit and assigned to a t-ethanol-acceptor, methanol-donor structure in an argon-backed expansion. In a helium-backed expansion, a second excited conformer has been observed, and tentatively assigned to a g-ethanol-acceptor, methanol-donor structure. No ethanol-donor, methanol-acceptor structures have been found, suggesting such structures are energetically disfavored.

Hydroperoxides are formed in the atmosphere following autooxidation of a wide variety of volatile organics emitted from both natural and anthropogenic sources. This raises the question of whether they can form hydrogen bonds that facilitate aerosol formation and growth. Using a combination of Fourier transform infrared spectroscopy, FT-IR, and ab initio calculations, we have compared the gas phase hydrogen bonding ability of tert-butylhydroperoxide (tBuOOH) to that of tert-butanol (tBuOH) for a series of bimolecular complexes with different acceptors. The hydrogen bond acceptor atoms studied are nitrogen, oxygen, phosphorus and sulphur. Both in terms of calculated redshifts and binding energies (BE), our results suggest that hydroperoxides are better hydrogen bond donors than the corresponding alcohols. In terms of hydrogen bond acceptor ability, we find that nitrogen is a significantly better acceptor than the other three atoms, which are of similar strength. We observe a similar trend in hydrogen bond acceptor ability with other hydrogen bond donors including methanol and dimethylamine.

Cations and anions, in solution, tend to pair up forming ion pairs. They play a crucial role in many fundamental processes in ion-concentrated solutions and living organisms. Despite their importance and vast applications in physics, chemistry and biochemistry, they remain difficult to characterize namely because of the coexistence of several types of pairing in solution. However, an interesting alternative consists in applying highly selective gas phase spectroscopy which can offer new insights on these neutral ion pairs. Our study consists in characterizing contact ion pairs (CIPs) in isolated model systems (M⁺, Ph-(CH₂)_n-COO⁻ with M=Li, Na, K, Rb, Cs, and n=1-3), to determine their spectral signatures and compare them to ion pairs in solution. We have used laser desorption to vaporize a solid tablet containing the desired salt. Structural information for each system was obtained by mass-selective, UV and IR laser spectroscopy combined with high level quantum chemistry calculations¹. Evidence of the presence of neutral CIPs was found by scanning the π-π* transition of the phenyl ring using resonant two-photon ionization (R2PI). Then, conformational selective IR/UV double resonance spectra were recorded in the CO₂⁻ stretch region for each conformation detected. The good agreement between theoretical data obtained at the BSSE-corrected-fullCCSD(T)/dhf-TZVPP//B97-D3/dhf-TZVPP level and experimental IR spectra led us to assign the 3D structure for each ion pair formed. Spectral signatures of (M⁺, Ph-CH₂-COO⁻) pairs, were assigned to a bidentate CIPs between the alkali cation and the carboxylate group. In the case of (Li⁺, Ph-(CH₂)₃-COO⁻) pairs, the presence of a flexible side chain promotes a cation-π interaction leading to a tridentate O-O-π structure with its unique IR and UV signatures. IR spectra obtained on isolated CIPs were found very much alike the ones published on lithium and sodium acetate in solution². However, in the case of sodium acetate, solution spectra were assigned to solvent shared pairs. Yet, the striking resemblance with our spectral data raises questions about the type assigned, pointing out that CIPs could be more present in these electrolyte solutions than previously thought. The novelty of the gas phase approach to investigate neutral ion pairs, opens the door for various new spectroscopic studies, paving the way to greater knowledge regarding the properties of ion pairs in many scientific fields. 1. Gloaguen, E.; Mons, M.; Topics in Current Chemistry, 2015, Vol 364, 225-270 2. Rudolph, W.W.; Fischer, D.; Irmer, G.; Dalton Transactions 2014, 43, (8), 3174-3185

In this study, ground states of antimony (Sb^v) with organic ligands complexes were studied by using density functional theory hybrid methods in order to obtain structural, electronic and vibrational spectral parameters. The mapping molecular electrostatic potential surface of the molecules computed to information about the charge density distribution of the molecules and its chemical reactivity. Frontier molecule orbital properties, HOMO and LUMO energies, global descriptors, and the total density of state diagram analysis were performed by using the time-dependent density functional theory. For the learning nonlinear optical properties, polarizability and hyperpolarizability tensors of the molecule were calculated.

r0pt Figure Accurate determination of the atmospheric abundance of hydrogen bound bimolecular complexes is necessary, as hydrogen bonds are partly responsible for the formation and growth of aerosol particles. The abundance of a complex is related to the Gibbs free energy of complex formation (∆G), which is often obtained from quantum chemical calculations that rely on calculated values of the enthalpy (∆H) and entropy (∆S) of complex formation. However, calculations of ∆H and in particular ∆S are associated with large uncertainties, and accurate experimental values are therefore crucial for theoretical benchmarking studies. Infrared measurements of gas phase hydrogen bound complexes were performed in the 300 to 373 K range, and lead to a purely experimental determination of ∆H using the van't Hoff equation. Equilibrium constants were determined by combining an experimental and calculated OH-stretching intensity, from which values of ∆G and hence ∆S could be determined. Thus we can determine ∆G, ∆H and ∆S for a bimolecular complex. We find that in the 300 to 373 K temperature range the determined ∆H and ∆S values are independent of temperature.

Boronyl (BO) is isoelectronic with CN, but its chemistry is much less known. One cause for the difficulty of the synthesis of boronyl complexes is that BO does not participate in π-backbonding with the d orbitals of transition metals due to an increased energy of the π^* orbital relative to CN or CO. Here we report a velocity map imaging study on TaBO⁻, the first observation of a BO ligand with an early transition metal. We observe transitions from the anion ground state (⁴∆) to two neutral states (⁵∆ and ³∆). We analyzed the chemical bonding in TaBO and compared it with TaCO. We found that there is a comparable amount of overlap between the d_xz and d_yz orbitals with the π^* orbitals of BO and CO. Our result suggests Ta may be better suited to bond with BO ligands to allow new transition metal boronyl complexes.