The microwave spectrum of the HCCH-2,6-difluoropyrine complex has been observed using a chirped pulse and conventional cavity-type Fourier transform microwave spectroscopy. The acetylene moiety forms a hydrogen bond to the nitrogen of the 2,6-difluoropyridine, and this structure is contrasted with several systems involving HCCH or CO₂ bound to pyridine or 2,6-difluoropyridine. The results of DFT calculations support the experimental observations and are reported as well. The chirped pulse spectrometer is new in our laboratory and is built in tandem with our cavity-type spectrometer with a design that allows for switching between the two modes of operation without having to break vacuum. Pertinent details of the spectrometer will also be given.

Nine isotopologues of Xe-SO₃ have been observed by pulsed-nozzle Fourier transform microwave spectroscopy. The complex is a symmetric top with a Xe-S van der Waals distance of 3.577(2) Å. The increase in rare gas distance relative to that in Kr-SO₃ is equal to the difference in van der Waals radii between Xe and Kr. The ¹³¹Xe nuclear quadrupole coupling constant indicates that the electric field gradient at the xenon nucleus is 78% larger than that at the Kr nucleus in Kr-SO₃.

The ground-state rotational spectra of the dimethyl sulfide-dimethyl ether (DMS-DME) and the ethylene oxide and ethylene sulfide (EO-ES) complexes were observed by Fourier transform microwave spectroscopy, and a-type and c-type transitions were assigned for the normal, ³⁴S, and three ¹³C species of the DMS-DME and a-type and b-type rotational transitions for the normal, ³⁴S, and two ¹³C species of the EO-ES. The observed transitions were analyzed by using an S-reduced asymmetric-top rotational Hamiltonian. The rotational parameters thus derived for the DMS-DME were found consistent with a structure of C_s symmetry with the DMS bound to the DME by two C-H(DMS)-O and one S-H-C(DME) hydrogen bonds. The barrier height V₃ to internal rotation of the "free" methyl group in the DME was determined to be 915.4 (23) cm⁻¹, which is smaller than that of the DME monomer, 951.72 (70) cm⁻¹, Y. Niide and M. Hayashi, J. Mol. Spectrosc. 220, 65-79 (2003).nd larger than that of the DME dimer, 785.4 (52) cm⁻¹. Y. Tatamitani, B. Liu, J. Shimada, T. Ogata, P. Ottaviani, A. Maris, W. Caminati, and J. L. Alonso, J. Am. Chem. Soc. 124, 2739-2743 (2002).or the EO-ES complex the observed data were interpreted in the terms of an antiparallel C_s geometry with the EO bound to the ES by two C-H(ES)-O and two S-H-C(EO) hydrogen bonds. We have applied a natural bond orbital (NBO) analysis to the DMS-DME and EO-ES to calculate the stabilization energy CT (= ∆Eσσ*), which were closely correlated with the binding energy E_B, as found for other related complexes.

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Y. Niide and M. Hayashi, J. Mol. Spectrosc. 220, 65-79 (2003).a Y. Tatamitani, B. Liu, J. Shimada, T. Ogata, P. Ottaviani, A. Maris, W. Caminati, and J. L. Alonso, J. Am. Chem. Soc. 124, 2739-2743 (2002).F

The rotational spectra of SF₆···NH₃ isotopologues have been observed in a pulsed nozzle chirped pulse Fourier-transform microwave spectrometer in the frequency range 6.5-18.5 GHz. The spectrum of SF₆···¹⁴NH₃ has been fitted to a Hamiltonian describing a symmetric top complex in which two symmetric top subunits undergo free internal rotation about a common symmetry axis. The distance between the centers of mass of the two monomers was found to be 4.15776(7) Å. Challenges associated with fitting mtransitions (correlating with K of free NH₃) for SF₆···¹⁴ND₃ imply complicated internal dynamics occurs within the complex.

Evidence for a complex between tetrahydrofuran (THF) and acetic acid from broadband rotational spectroscopy will be presented. Transitions believed to belong to the complex were first identified in a gas mixture containing small amounts of THF, triethyl borane, and acetic acid balanced in argon. Ab initio calculations suggest a complex between THF and acetic acid is more likely to form compared to the analogous acetic acid complex with triethyl borane, the initial target. The observed rotational constants are also more similar to those predicted for a complex formed between THF and acetic acid, than for those of a complex formed between triethyl borane and acetic acid. Subsequently, multiple isotopologues of acetic acid have been measured, confirming its presence in the structure. No information has yet been obtained through isotopic substitution within the THF sub-unit. Ab initio calculations predict the most likely structure is one where the acetic acid subunit coordinates over the ring creating a "bridge" between the THF oxygen, the carboxylic O-H, and the carbonyl oxygen to a hydrogen atom on the back of the ring.

The rotational spectrum of three 1:1 complexes of pyridine with formic acid has been observed and assigned using pulsed jet Fourier transform microwave technique. The two subunits are held together through one O-H···N hydrogen bond and one C-H···O weak hydrogen bond, forming a seven-membering cyclic structure. The rotational spectrum of the pyridine-HCOOD isotopologue is considerably shifted towards lower frequencies, with respect to the "rigid" model, suggesting a considerable Ubbelohde effect, similar in nature to that observed in the bi-molecules of carboxylic acids.

Fourier-Transform microwave (FTMW) spectroscopy has been applied to observe the J = 1 - 0 rotational transitions of the H₂-HCN/DCN complexes containing both the para-H₂ (I_H2=0) and ortho-H₂ (I_H2=1) moleculeM. Ishiguro et al., Chem. Phys. Lett. 554, 33 (2012). Rotational spectra of H₂-HCN/DCN up to J = 5 - 4 were also observed in the millimeter-wave (MMW) region below 180 GHzM. Ishiguro et al., J. Chem. Phys. 115, 5155 (2001). Observed FTMW lines for H₂-HCN/DCN split into hyperfine components due to the nuclear quadrupole interaction of N and D nuclei. For the ortho-H₂ species, the hyperfine splitting due to the magnetic interaction between the hydrogen nuclear spin of ortho-H₂ part (j_H2=1, I_H2=1) was also observed, but not for the para-H₂ species (j_H2=0, I_H2=0). From the observed nuclear spin-spin coupling constants of ortho-H₂ species, d = 21.90(47) and 24.66(68) kHz for HCN and DCN complexes, respectively, the average values of < P₂ (cos θ) > = 0.380(8) and 0.439(10) were derived indicating the nearly free rotation of H₂ in the complex with j_H2= 1 and k_H2= 0. The nuclear quadrupole interaction constants due to N and D nuclei show that the HCN/DCN part executes a floppy motion with a large mean square amplitude of about 29/25 and 33/30 degree in the para and ortho species, respectively. From the observed rotational constants, the center-of-mass distances of H₂ and HCN/DCN were derived to be 3.9617(5)/4.00356 (43) Å   for the ortho species and 4.1589(13)/4.1596 (36) Å  for the para species. The isotope effect on rotational constants confirmed the totally different configurations in the ortho and para species: H₂ is attached to the H/D end of HCN/DCN for the para species, while to the N end for the ortho species, as suggested by IR spectroscopy and theoretical study.

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M. Ishiguro et al., Chem. Phys. Lett. 554, 33 (2012).. M. Ishiguro et al., J. Chem. Phys. 115, 5155 (2001)..

Observations of gas-phase dimers are one of the simplest methods for studying bimolecular interactions. These dimers are excellent model systems for molecular interactions, providing a benchmark for theoretical studies, and a basis for understanding and modeling more complex interactions. Of particular interest are studies of strong (O-H…O-H) and weak (C-H…O-H) long-range interactions of water. We have recently recorded the pure rotational spectrum of the cyclopentanol-water dimer with chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW). We will present the spectrum of this dimer and discuss its structure in the context of C-H…O-H and O-H…O-H bonding.

The conformational energy landscape of the ethanol-water dimer is determined by the relative hydrogen-bond donor and acceptor strengths of the two molecules, as well as weaker hydrophobic interactions between the water and the ethyl group. Using a combination of ab initio calculations and chirped-pulse Fourier transform microwave spectroscopy, we have recorded the first rotationally-resolved, jet-cooled spectrum of the ethanol-water dimer between 8-18.5 GHz and identified two water-donor ethanol-acceptor conformers. The lowest energy conformer is chiral, has ethanol in the gauche configuration, and is consistent with previous raman and infrared results.Nedić, Marija, et al. PCCP 13.31 (2011): 14050-14063.he second conformer corresponds to the trans-ethanol configuration, and exhibits a significant splitting.

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Nedić, Marija, et al. PCCP 13.31 (2011): 14050-14063.T

Acetonitrile, CH₃CN, and trifluoroacetonitrile, CF₃CN, are symmetric tops. In a recent study of the rotational spectrum of the acetonitrile and water complex, it was observed that the structure was also an effective symmetric topLovas, F.J.; Sobhanadri, J. Microwave rotational spectral study of CH₃CN−H₂O and Ar−CH₃CN. J. Mol. Spetrosc. 2015, 307, 59-64. with the external hydrogen freely rotating about the O−H bond aligned towards the nitrogen of the cyanide of CH₃CN. Unlike the CH₃CN−H₂O complex, the CH₃CN−Ar and CF₃CN−Ar complexes were observed to be asymmetric tops. Having a series of symmetric and asymmetric top complexes of acetonitrile and trifluoracetonitrile for comparison, we report the rotational spectrum of the weakly bound complex between trifluoroacetonitrile and water. Rotational constants and quadrupole coupling constants will be presented, and the structure of CF₃CN−H₂O will be revealed. SPOILER ALERT: It's an asymmetric top. Lovas, F.J.; Sobhanadri, J. Microwave rotational spectral study of CH₃CN−H₂O and Ar−CH₃CN. J. Mol. Spetrosc. 2015, 307, 59-64.,

A recent investigation of the HOD−N₂O complex measuring the OH + OD excited band in the near-IR was completed by Foldes et al.Földes, T; Lauzin, C.; Vanfleteren, T.; Herman, M.; Lièvin, J.; Didriche. K. High-resolution, near-infrared CW-CRDS and ab initio investigations of N₂O−HDO.Mol. Phys. 2015, 113(5),473-482.uring this study, one of us (WAK) was contacted about the position of deuterium in the HOD−N₂O complex, as his group completed the original microwave study of H₂O−N₂O and its deuterated isotopologuesZolandz, D.; Yaron, D.; Peterson, K.I.; Klemperer, W. Water in weak interactions: The structure of the water-nitrous oxide complex. J. Chem. Phys. 1992, 97,2861.n 1992. The results of this microwave study did not give the orientation of HOD in the complex, however, we present here a supplementary study to the original microwave work using a Balle-Flygare cavity instrument, attempting to determine the orientation of HOD relative to the N₂O. In addition to a Kraitchman and a least-squares inertial structure fit of the molecule, we present the nuclear quadrupole coupling tensor of deuterium to determine the position of HOD in the complex.

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Földes, T; Lauzin, C.; Vanfleteren, T.; Herman, M.; Lièvin, J.; Didriche. K. High-resolution, near-infrared CW-CRDS and ab initio investigations of N₂O−HDO.Mol. Phys. 2015, 113(5),473-482.D Zolandz, D.; Yaron, D.; Peterson, K.I.; Klemperer, W. Water in weak interactions: The structure of the water-nitrous oxide complex. J. Chem. Phys. 1992, 97,2861.i

r0ptFigureWhile searching for the chirped pulse spectra of allyl phenyl ether, the authors used current rotational spectroscopic fitting tools to assign multiple sets of spectra of unknown origin. Previous chirped pulse experiments searching for hydrate complexes of perfluoropropionic acid had not been successful but, through theoretical agreement, it was determined that at least one of the sets of unknown spectra observed belonged to the perfluoropropionic acid-water complex. Further determination showed that the dihydrate had also been observed. The determination process and spectral assignment will be discussed. Structural determinations of the complexes will also be discussed.

r0pt Figure Both amine and hydroxyl functional groups are present in 4-aminophenyl ethanol (4-AE), and each functional group can form hydrogen bonds with carboxylic acids, such as formic acid and acetic acid. Predicting the structures of such complexes involving 4-AE is rather complex, given the many possible conformations and their similar (and method and basis-dependent) energies. In particular, the carboxyl group, -COOH, can act as both as a hydrogen bond donor or acceptor, or both at once. In this study we report the formic acid − 4-AE hydrogen bonded complex. An infrared-ultraviolet double resonance spectrometer is used to examine the shifts in IR frequencies of 4-AE from the monomer to the complex. Fourier transform microwave spectroscopy is used to determine structures of the species. Results from both experiments are compared to DFT and ab initio results. Time permitting, results of the water complex with 4-AE will also be presented.

Previous studies have found that gold atom and boronyl bear similarities in bonding in many gas phase clusters.H.-J. Zhai, C.-Q. Miao, S.-D. Li, L.-S. Wang, J. Phys. Chem. A 2010, 114, 12155–1216Q. Chen, H. Bai, H.-J. Zhai, S.-D. Li, L.-S. Wang, J. Chem. Phys. 2013, 139, 044308H. Bai, H.-J. Zhai, S.-D. Li, L.-S. Wang, Phys. Chem. Chem. Phys., 2013, 15, 9646–9653H.-J. Zhai, Q. Chen, H. Bai, S.-D. Li, L.-S. Wang, Acc. Chem. Res. 2014, 47, 2435-2445B₁₀(BO), B₁₂(BO), B₃(BO)_n (n=1, 2) were found to possess similar bonding and structures to B₁₀Au, B₁₂Au, B₃Au_n (n=1, 2), respectively. During the recent photoelectron spectroscopy experiments, the spectra of BiBO⁻ and BiAu⁻ clusters are found to exhibit similar patterns, hinting that they possess similar geometric structures. While BiAu⁻ is a linear molecule, BiBO⁻ is also linear. The similarity in bonding between BiBO⁻ and BiAu⁻ is owing to the fact that Au and BO are monovalent σ ligands. The electron affinities are measured to be 1.79±0.04eV for BiBO⁻ and 1.36±0.02eV for BiAu⁻. The current results provide new examples for the BO/Au isolobal analogy and enrich the chemistry of boronyl and gold.

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H.-J. Zhai, C.-Q. Miao, S.-D. Li, L.-S. Wang, J. Phys. Chem. A 2010, 114, 12155–1216  Q. Chen, H. Bai, H.-J. Zhai, S.-D. Li, L.-S. Wang, J. Chem. Phys. 2013, 139, 044308  H. Bai, H.-J. Zhai, S.-D. Li, L.-S. Wang, Phys. Chem. Chem. Phys., 2013, 15, 9646–9653  H.-J. Zhai, Q. Chen, H. Bai, S.-D. Li, L.-S. Wang, Acc. Chem. Res. 2014, 47, 2435-2445