Noncovalent interactions of aromatic complexes are highly significant in biological systems such as DNA, in materials science and in supramolecular chemistry. Gas phase studies of small aromatic complexes allow the determination of their preferred structural arrangements and of the relative contributions of various intermolecular forces to the interaction energy, laying the foundation for understanding the properties and interactions of larger systems. Azulene is one of the smallest aromatic hydrocarbons with a dipole moment. Here we present the investigation of azulene aggregation and its interactions with water using chirped-pulse Fourier transform microwave spectroscopy. We have observed one and two water molecules complexed with azulene, where water binds to azulene through an O-H…π hydrogen bond. Azulene dimer shows a stacked configuration where dispersion forces between the π electronic densities are predominant. Experimental observations are compared with predictions by various theoretical methods to evaluate their performance.

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.

Linear ternary carbon-rich clusters have attracted some attention as possible astronomical species as well as benchmark systems for quantum-chemistry. As such they have been studied to some extent also using high-resolution spectroscopic techniques (e.g., SiC_nS chains)P. Botschwina, M. E. Sanz, M. C. McCarthy, and P. Thaddeus, J. Chem. Phys. 116, 10719 (2002). In the present study, recent results from a 5μm high-resolution infrared study of laser ablation products from carbon-selenium-sulfur targets will be presented. Complementary results from high-level quantum chemical calculations will also be discussed.

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Footnotes:

P. Botschwina, M. E. Sanz, M. C. McCarthy, and P. Thaddeus, J. Chem. Phys. 116, 10719 (2002)..

A series of strong bands in the 900-2200 cm⁻¹ 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. A 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.C. Light, I.P. Hamilton, and J. V. Lill, J. Chem. Phys. 82, 1400 (1985).A

2,2,3,3,3-pentafluoropropanol (PFP) is an important solvent for organic syntheses. It is also considered to be a greenhouse gas pollutant because it is radiatively active in the mid-infrared region. Understanding properties of PFP and its hydrogen bonding interactions with water in the gas phase may help to develop more realistic estimate of its effects because of the abundance of water in the atmosphere. In the current study, we apply both rotational spectroscopy and ab initio calculations to characterize large amplitude motions in PFP and its water complex and also hydrogen bonding interactions between PFP with water. Their rotational spectra were recorded using a cavity-based and a chirped pulse Fourier transform microwave spectrometers. Two most stable PFP conformers, Pg+g+ and Ptg+ were identified. The rotational transitions of the latter exhibit tunneling splittings. Two PFP···H2O conformers were identified and both of them show tunneling splittings. Deuterated species of the water complex were also investigated to assist the identification of the tunneling paths, in addition to the theoretical calculations. The large amplitude motions responsible for these splittings will be discussed.

The microwave spectrum of the NH₃−Ne van der Waals complex has been observed in a supersonic molecular jet expansion via broadband (2-8 GHz) chirped-pulse Fourier-transform microwave spectroscopy. Together with the well-known lines related to the (ortho)-NH₃−Ne spectrumJ. van Wijngaarden and W. Jäger, J. Chem. Phys. 115, 6504 (2001). new transitions were detected and attributed to the missing (para)-NH₃−Ne nuclear spin isomer. The assignments were guided by the rovibrational bound state (J = 0 ... 10) calculations based on the recent ab initio NH₃−Ne intermolecular potential surfaceJ. Loreau and A. van der Avoird, J. Chem. Phys. 143, 184303 (2015). The hyperfine structure arising from quadrupole ¹⁴N nucleus of NH₃−Ne was resolved, and the quadrupole coupling constant associated with the (para)-NH₃ subunit was precisely determined. This constant provided the dynamical information about the angular orientation of ammonia indicating that the average angle between the C₃ axis of NH₃ and intermolecular axis is about 68^°. Similar results for the deuterated isotopologue, ND₃−Ne, were also obtained thus confirming and extending the analysis for the parent NH₃−Ne complex.

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Footnotes:

J. van Wijngaarden and W. Jäger, J. Chem. Phys. 115, 6504 (2001)., J. Loreau and A. van der Avoird, J. Chem. Phys. 143, 184303 (2015)..

1,4-Naphthoquinone (NTQ) is an important product of naphthalene oxidation and it also appears as a motif in many biologically active compounds. NTQ is introduced into the atmosphere by direct emissions from combustion of organic matter, and as a result of reactions of polycyclic aromatic hydrocarbons in the troposphere. Here we present a study of NTQ and its interactions with water using broadband rotational spectroscopy. Bare NTQ and its complexes with one, two and three water molecules have been detected. Their structures and relative arrangements have been determined by using ¹⁸O isotopic data aided by theoretical calculations. Water molecules have been found to adapt their arrangement with respect to NTQ to maximise primary and secondary interactions, with more efficient competition between in-plane and above-plane complex configurations as the number of water molecules increase.

The dissociative electron dynamics of transition metal oxide clusters provide information about the stability and reactivity of their bulk material counterparts. Ti, Fe, and Ni oxides are widely used catalytic materials which may be improved with the detailed atomic precision of their stable conformations and low energy electron properties. In our experiments, neutral Ti_nO_m, Fe_nO_m, and Ni_nO_m oxide clusters are produced with small amounts of oxygen and their mass spectra show a primary stable stoichiometry of m = n for Fe clusters, m = n - 1 for Ni clusters, and m = 2n - 1 for Ti clusters. I will present our ultrafast pump-probe spectroscopy measurements on the direct ionization, dissociation, formation, and excitation-relaxation properties for these metal cluster systems extending up to n = 10. The femtosecond dynamics observed for these clusters depend strongly on their metal composition, size, and oxidation state. Understanding the energy and time-resolved fragmentation patterns of large molecules may prove to produce more targeted catalysts of increased reactivity, leading to decreased cost and waste.

Solvation of H₃O⁺ is an interesting and important problem in Chemical Physics. To gain a better understanding of the vibrational coupling in solvated H₃O⁺, many studies using gas-phase Infra-Red Pre-Dissociation (IRPD) spectroscopy have been attempted. In experimental spectra of H₃O^+...Ar₃, a prounced splitting of O-H stretching near 3300 cm⁻¹is attributed to Fermi Resonance with overtone of bending. But a peculiar band at similar frequency observed in H₃O^+...(N₂)₃ has been assigned to be a combination band with hydrogen-bonded stretching modes. To gain further insight into the mechanism of these two types of anharmonic coupling, we have measured IRPD spectra of H₃O^+...Kr₃, and H₃O^+...(CO)₃. Ab Initio Anharmonic Algorithms have been applied to H₃O^+...X₃, (X=Ne, Ar, Kr, N₂, CO and H₂O) to examine the interplay between Fermi resonance and combination band.