The meta-anisic acid and its complexes with formic acid have been studied in the 2-15 GHz frequency region using chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW). For meta-anisic acid, four conformations have been identified. The four conformations resulting from the possible arrangements of the caboxylic and methoxy groups have been identified. In addition, the spectra of mixtures of meta-anisic acid and formic acid were investigated. Four species were found where formic acid is attached to the acid group through two O-H···O=C complementary hydrogen bonds. These complexes correspond to the four meta-anisic acid stable structures that seem to be not essentially modified after the complexation process.

2-Cyanoacetic acid (m.p. 67-73 ^°C), a molecule with astrochemical significance and structural similarities to glycineI. D. Reva, S. G. Stepanian, L. Adamowicz and R. Fausto, J. Phys. Chem A 2003 107, 6351-6359as been transferred into the gas phase by heating and supersonic expansion. Possible conformational relaxation paths were explored by using different buffer gases such as neon, argon, and helium. Rotational constants were found using chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW). 2-Cyanoacetic acid possesses one 14N nucleus with a nuclear quadrupole moment, giving rise to a complex hyperfine structure. To assist with spectral fitting, AutofitN. A. Seifert, I. A. Finneran, C. Perez, D. P. Zaleski, J. L. Neill, A. L. Steber, R. D. Suenram, A. Lesarri, S. T. Shipman, and B. H. Pate J. Mol. Spec. 2015 312, 12-21as used. One stable conformer of the monomer and its complex with a water molecule have been identified on the basis of the experimental rotational constants in conjunction with DFT and ab initio predictions.

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I. D. Reva, S. G. Stepanian, L. Adamowicz and R. Fausto, J. Phys. Chem A 2003 107, 6351-6359h N. A. Seifert, I. A. Finneran, C. Perez, D. P. Zaleski, J. L. Neill, A. L. Steber, R. D. Suenram, A. Lesarri, S. T. Shipman, and B. H. Pate J. Mol. Spec. 2015 312, 12-21w

The rotational spectrum of the weakly bound complex between xenon and carbonyl sulfide has been measured using a coaxially oriented beam resonator arrangement (COBRA) Fourier transform microwave spectrometer in Hannover. There are nine naturally occurring isotopes of xenon in addition to the many possible isotopologues of carbonyl sulfide, which allows for a detailed analysis of the structure of the van der Waals complex and subsequent comparisons to other rare gas van der Waals complexes with carbonyl sulfide that have already been reported. Of the nine isotopes of xenon, two have non-zero nuclear spins, ¹³¹Xe (I=3/2) and ¹²⁹Xe (I=1/2). In the case of the ¹³¹Xe, a hyperfine structure was observed in all transitions, revealing a non-zero field gradient at the xenon nucleus in the complex. High-level ab initio calculations were carried out to identify an accurate method for the prediction of the structure of the complex and the nuclear quadrupole coupling constants of ¹³¹Xe. The van der Waals interaction energies of xenon and carbonyl sulfide will be discussed.

The Ar-CH₃I complex has been observed by pulsed-nozzle Fourier transform microwave spectroscopy. The rotational spectrum is complicated by both the low internal rotation barrier of the methyl group and the large nuclear quadrupole coupling from the iodine. The identification of closed loops was essential to the successful analysis of 140 observed transitions which have been assigned to the A internal rotor state of the complex. An additional 102 observed transitions are likely due to the E internal rotor state. Associated computational work, as well as ongoing attempts to assign the E state spectrum, will be discussed.

2-Phenylpyridine (2pp) is well known as an organic ligand in metal complexes, systems which present a relevant importance in fields such as inorganic photochemistry, biological electron-transfer dynamics or, for example, as chromophores in semiconductor assemblies in solar energy panels. The analysis of the rotational spectra of the parent and all the ¹³C and ¹⁵N isotopologues for the 2pp, split by the torsional vibration, have allowed us to determine the structure of 2pp. Furthermore, it has been possible to detect the spectra of the 1:1 and 1:2 water complexes. For the 1:1 adduct, the spectra of the parent and the same isotopologues as observed for the monomer have been measured. This has enabled direct structural comparison between the bare molecule and its water complex, determining how the water affects the structure of 2pp.

Formanilide (C₇H₇NO) is a molecule that mimics the -NH-CO- peptide bond. It adopts two different conformations, planar or non-planar, depending respectively on the trans or cis arrangement of the peptidic group. Formanilide offers a variety of hydrogen bond binding sites so its microsolvated clusters can be taken as good models to investigate the interaction of the peptide functional group with water. In this work, the rotational spectra of formanilide-(H₂O)_n (n=1, 2) complexes have been studied in the 2-12.5 GHz frequency range using both a pulsed-chirp and a molecular beam Fourier transform microwave spectrometers. Three heterodimers, cis-1:1a trans-1:1b and trans-1:1c forms and one heterotrimer, cis-1:2a, have been observed. The rotational spectra of the parent, several D/H and ¹⁸O/¹⁶O isotopically substituted species have been measured for the adducts in order to investigate their structures. All species are characterized by the quadrupole coupling hyperfine structure due to the presence of a ¹⁴N atom in formanilide. The rotational spectra of some species show small doublets attributable to either intramolecular motions within the formanilide subunit, as occur in cis-1:1a, or to intermolecular motions as the internal rotation of water in form trans-1:1c.

The rotational spectra of the styrene-water complex has been investigated by using the pulsed jet Fourier transform microwave spectroscopic technique. Styrene has two π systems which can act as the proton acceptor and link with water through the OH-π hydrogen bond. Ab initio calculations suggested that the vinyl π system is favored to form such a hydrogen bond. In contrast, the experimental evidences of four isotopologues pointed out that the water O-H group prefers to link to the benzene π system. The internal rotation of water around its symmetry axis splits all the rotational transitions into two component line with a relative intensity ration of 1:3.

Fenchol C₁₀H₁₈O was identified as one of the many products emitted by several plants, by pin radiata wood, and by fibers panels N. Yassa et al, Atmos. Env. 34, 2809 (2000) ; A. G. McDonald et al, Holz als Roh und Werkstoff 64, 291 (2004) ; M. G. D. Baumann, Forest products journal 50, 75 (2000). It is a monoterpene of spectroscopic interest in order to determine the more stable conformer. Indeed the fenchol molecule presents two stereoisomers depending on the position of the OH group and of the hydrogen atom, named endo- and exo-fenchol. In the present work, we present the conformational landscape study of fenchol in order to identify in the gas phase the more stable conformer for each stereoisomer. A combination of theoretical calculations and Fourier transform microwave spectroscopy in a supersonic molecular jet was used. Because of a disagreement between the different calculation methods for the endo-fenchol stereoisomer, fenchol-D was used to identify the most stable conformer. The hyperfine structure signature was found very helpful. Moreover the hydration of endo-fenchol was studied. The multi-isotopic substitution of deuterium has led to identify the observed conformer. Surprisingly the substituted structure of the hydrogen atoms shows that the observed complex is formed by hydrogen bonding between the high energy conformer of endo-fenchol - which is not observed in the jet - with the water molecule. The set of molecular parameters was adjusted using a Watson Hamiltonian in the A reduction to the experimental accuracy. The present work was funded by the French ANR Labex CaPPA through the PIA (contract ANR-11-LABX-0005-01), by the Regional Council Hauts de France, by the European Funds for Regional Economic Development (FEDER), and by the French Ministère de l'Enseignement Supérieur et de la Recherche. It is a contribution to the CPER research Project CLIMIBIO.

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Footnotes:

N. Yassa et al, Atmos. Env. 34, 2809 (2000) ; A. G. McDonald et al, Holz als Roh und Werkstoff 64, 291 (2004) ; M. G. D. Baumann, Forest products journal 50, 75 (2000)..

The rotational spectrum of methyl carbamate has been recorded in the 2-8 GHz frequency region using a chirped-pulse Fourier transform microwave spectrometer. The carrier gas was seeded with water and methyl carbamate vapors for the formation of microsolvated complexes. Complexes with one and two molecules of water have been detected. Both spectra show the fine structure arising from the internal rotation of the methyl top together with the hyperfine structure due to the presence of one ¹⁴N nucleus. The spectra were further registered in the 5-18 GHz frequency region by the higher resolution supersonic expansion cavity Fourier transform microwave spectroscopy to analyze more accurately the hyperfine structure. The determined rotational parameters provide the key for the identification of the complexes in the light of ab initio computations. Both the methyl group internal rotation barrier and the quadrupole coupling constants show interesting trends in going from isolation to the microsolvated complexes.

Measuring the structure of molecular dimers is a stepping stone in the study of chemical interactions. These structures are normally highly sensitive to the two-body potential and therefore form a basis for interpreting structure, dynamics, and reactions in more complex systems. Studies of strong and weak hydrogen bonded clusters have provided important insight into the nature of these interactions. The structures of numerous dimers have been determined, however many complexes, especially those involving weakly polar species such as isoprene, have not been measured. Isoprene(C₅H₈), the simplest terpene, is the building block for terpenes and terpenoids, many of which are volatile compounds released by trees and shrubs. Isoprene accounts for 50% of biogenic non-methane hydrocarbon emission, and is therefore a major contributor to aerosol production. Furthermore, the composition of isoprene-derived aerosols varies significantly with relative humidity. The study of the structure of heterogeneous isoprene clusters is therefore of considerable interest for furthering our understanding of the interactions that drive isoprene chemistry. Towards this end, we will present the pure rotational spectrum of the isoprene-water complex recorded with a chirped-pulse Fourier transform microwave spectrometer, and discuss the structure of the complex.