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We used high-resolution rotational spectroscopy coupled to a laser ablation source to study the conformational panorama of perillartine, a solid synthetic sweetener. Four conformers were identified under the isolation conditions of the supersonic expansion, showing that all of them present an E configuration of the C=N group with respect to the double bond of the ring. The observed structures were verified against Shallenberger–Acree–Kier’s sweetness theory to shed light on the structure–sweetness relationship for this particular oxime, highlighting a deluge of possibilities to bind the receptor.

Producción Científica, The metallic cyanoacetylides LiC3N, NaC3N, MgC3N, and CaC3N have been investigated by combined spectroscopy measurements and theoretical calculations. The theoretical calculations predict for the four species that the linear isomer with the formula MCCCN (M = Li, Na, Mg, and Ca) is the most stable one. We used laser ablation molecular beam Fourier transform microwave (FTMW) spectroscopy to synthesize these species by the reaction of metal vapors, produced by laser ablation, and 3-bromo-2-propynenitrile (BrCCCN). Pure rotational spectra were observed by FTMW spectroscopy in the 2–18 GHz frequency region only for LiCCCN and NaCCCN, while no spectral signatures for MgCCCN and CaCCCN could be detected. Finally, we have searched for LiCCCN and NaCCCN species toward the carbon-rich evolved star IRC +10 216, but only upper limits to their abundances have been obtained., Consejo Europeo de Investigación a través del VII Programa Marco de Investigación y Desarrollo (grant 610256 NANOCOSMOS), Ministerio de Economía, Industria y Competitividad (grants CTQ 2013-40717-P / CTQ 2013-76393-P / AYA2017-87515-P / Consolider-Ingenio 2010 CSD2009-00038), Junta de Castilla y León (grants VA175U13 / VA010G18 / VA077U13)

Solid samples of phenylglycinol were vaporized by laser ablation and investigated through rotational spectroscopy in a supersonic expansion using two different techniques: chirped pulse Fourier transform microwave spectroscopy and narrow band molecular beam Fourier transform microwave spectroscopy. One conformer, bearing an O–H···N and an N–H···π intramolecular hydrogen bonds, could be successfully identified by comparison of the experimental rotational and 14 N nuclear quadruple coupling constants with those predicted theoretically.

In this paper we report the first rotational spectrum of isolated paracetamol. Solid samples of paracetamol were vaporized by laser ablation, expanded in a supersonic jet and characterized by Fourier transform microwave spectroscopy in the 4-10 GHz frequency range. The spectra of a total of four conformers, two with a trans peptidic -CO-NH- functional group arrangement and two with a cis peptidic group arrangement have been observed for the first time. The identification of all the conformers was based on the comparison of the experimental rotational and (14)N quadrupole coupling constants with those predicted by ab initio calculations, and relative values of their electrical dipole moment components.

The rotational spectrum of neutral dopamine has been investigated for the first time using a combination of Fourier transform microwave spectroscopy with laser ablation. The parameters extracted from the analysis of the spectrum unequivocally identify the existence of seven conformers of dopamine. (14)N nuclear quadrupole coupling interactions have been used to determine the orientation of the amino group probing the existence of stabilizing N-H···π interactions for all observed conformers.

The conformational behaviour of naturally occurring ketohexoses has been revealed in a supersonic expansion by Fourier transform microwave spectroscopy coupled with a laser ablation source. Three, two and one conformers of d-tagatose, d-psicose and l-sorbose, respectively, have been identified by their rotational constants extracted from the analysis of the spectra. Singular structural signatures involving the hydroxyl groups OH(1) and OH(2) have been disentangled from the intricate intramolecular hydrogen bond networks stabilising the most abundant conformers. The present results place the old Shallenberger and Kier sweetness theories on a firmer footing.

Structural signatures for exo-anomeric effect have been extracted from the archetypal methyl-β-D-xyloside using broadband Fourier transform microwave spectroscopy combined with laser ablation. Spectrum analysis allows the determination of a set of rotational constants, which has been unequivocally attributed to conformer cc-β-(4)C1 g-, corresponding to the global minimum of the potential energy surface, where the aglycon residue (CH3) orientation contributes to maximization of the exo-anomeric effect. Further analysis allowed the determination of the rs structure, based on the detection of 11 isotopologues--derived from the presence of six (13)C and five (18)O atoms--observed in their natural abundances. The observed glycosidic C1-O1 bond length decrease (1.38 Å) can be interpreted in terms of the exo-anomeric effect. As such, the exo-anomeric effect presents itself as one of the main driving forces controlling the shape of many biologically important oligosaccharides.

Using a combination of laser ablation and jet cooled FT-MW spectroscopy the pure rotational spectrum of AlCCH and AgCCH in the (X1Σ+) electronic ground state has been recorded and assigned in the 6–20 GHz region. A newly constructed ablation-discharge source has been coupled to our LA-MB-FTMW spectrometer and tested as a generator of metal acetylides. Laser ablation of the pure metal has been demonstrated as a very efficient method to create unstable compounds in the gas phase. The high spectral resolution of our instrument provided an accurate set of rotational, quadrupole (only for AlCCH) and centrifugal distortion constants which are reported for the first time.

The rotational spectrum of neutral phenylalanine has been recorded for the first time using laser-ablation molecular-beam Fourier transform microwave spectroscopy (LA-MB-FTMW). Two conformers stabilized by conjugative O-H···N and N-H···π hydrogen bond interactions have been conclusively identified on the basis of experimental values of rotational and (14)N nuclear quadrupole coupling constants. The nonobservation of the rotational spectra of the other low-energy conformers has been attributed to the photofragmentation that takes place in the laser ablation process. Nuclear quadrupole coupling interactions have been used directly to determine the orientation of the amino group and to identify and experimentally characterize the N-H···π interactions.

Rotational spectroscopy in combination with molecular beams and laser ablation (laser-ablation molecular-beam Fourier transform microwave (LA-MB-FTMW) spectroscopy) has proved to be successful in characterizing the conformers of natural amino acids. The procedure usually followed to assign and identify the different conformers of an amino acid from the rotational spectrum is described through the study of the natural amino acid L-threonine. The solid sample of L-threonine was vaporized by laser pulses, diluted in Ne and supersonically expanded between the mirrors of a Fabry-Pérot resonator where it was spectroscopically probed by microwave radiation. The rotational and nuclear quadrupole coupling constants extracted from the analysis of the rotational spectrum are directly compared with those predicted by ab initio methods to achieve the conclusive identification of seven different conformers. A complex hydrogen bonding network arises as a consequence of the polar side chain of threonine.

Seven conformations of the neurotransmitter p-methoxyphenylethylamine have been observed in a supersonic jet using molecular beam Fourier transform microwave spectroscopy (MB-FTMW). The 14 N nuclear quadrupole coupling hyperfine structure has been resolved for all conformers. The comparison between the experimental and ab initio data, especially the quadrupole coupling constants, has provided a conclusive test for the identification of all observed conformers.

We report on the tentative detection of $trans$ Ethyl Methyl Ether (tEME), $t-CH_3CH_2OCH_3$, through the identification of a large number of rotational lines from each one of the spin states of the molecule towards Orion KL. We also search for $gauche$-$trans$-n-propanol, $Gt-n-CH_3CH_2CH_2OH$, an isomer of tEME in the same source. We have identified lines of both species in the IRAM 30m line survey and in the ALMA Science Verification data. We have obtained ALMA maps to establish the spatial distribution of these species. Whereas tEME mainly arises from the compact ridge component of Orion, Gt-n-propanol appears at the emission peak of ethanol (south hot core). The derived column densities of these species at the location of their emission peaks are $\leq(4.0\pm0.8)\times10^{15} cm^{-2}$ and $\leq(1.0\pm0.2)\times10^{15} cm^{-2}$ for tEME and Gt-n-propanol, respectively. The rotational temperature is $\sim100 K$ for both molecules. We also provide maps of $CH_3OCOH$, $CH_3CH_2OCOH$, $CH_3OCH_3$, $CH_3OH$, and $CH_3CH_2OH$ to compare the distribution of these organic saturated O-bearing species containing methyl and ethyl groups in this region. Abundance ratios of related species and upper limits to the abundances of non-detected ethers are provided. We derive an abundance ratio $N(CH_3OCH_3)/N(tEME)\geq150$ in the compact ridge of Orion., Accepted in A&A Letters

The characterization of tellurium selenide in its electronic ground state (X0 + ∑ − ) was possible by using LASER-ablation to isolate the diatomic in a pulsed molecular beam and by applying Fourier transform microwave spectroscopy to obtain the pure rotational spectrum. Employing a global multi-isotopologue analysis to transitions of 43 isotopologues of TeSe in seven vibrational states spectroscopic Dunham parameters Y l , m , Born–Oppenheimer breakdown coefficients δ l , m , the equilibrium bond lengths r e , as well as the vibration parameters ω e and ω e x e were obtained for all analysed isotopologues. For low vibrational states, the Morse-potential function describes the TeSe-potential very well and provides an estimate of the maximum dissociation energy for this semi-metal compound. In addition, the isotopologue independent molecular constants U l , m and the corresponding Born–Oppenheimer breakdown coefficients Δ l , m were determined. Quite large coefficients Δ 0 , 1 Te and Δ 0 , 1 Se were necessary for Watson's reference isotopologue independent analysis. This is rationalized by the interaction between the two sublevels of the electronic 3 Σ-state. Also the magnetic spin–rotation coupling constants that were achieved for some of the isotopologues reflect this electronic ground state. Field shift effects are found to be negligible.

Cyclohexene oxide and its hydrogen bonded complex cyclohexene oxide⋯HCl have been investigated using a molecular beam Fourier Transform microwave spectrometer. The spectra of the parent species of cyclohexene oxide and its 13 C and 18 O isotopomers have been measured in their natural abundances. This has allowed obtaining the substitution and effective structures of the monomer heavy atom skeleton. A fast mixing nozzle has been designed to generate the complex preventing the reaction between the components. Only the equatorial conformer of the complex has been detected and its 35 Cl and 37 Cl isotopic species have been measured in their natural abundances. From the spectroscopic data the hydrogen bond structural parameters were obtained assuming that the structures of the monomers do not change upon complexation. HCl lies in the COC bisecting plane forming a non-linear hydrogen bond to the equatorial non-bonding electron pair at oxygen. The geometries of the axial and equatorial conformers have been optimized at MP2/6-311++G(d,p) level of theory predicting the equatorial conformer as the most stable one. The non-observation of the axial form is discussed.

The Fourier transform rotational spectra of the normal and the 13 C species of the 1:1 complex between difluoromethane and water have been measured. The rotational transitions are split into two component lines, due to the internal rotation of the water moiety. The barrier to this motion has been estimated to be 340(20) cm −1 . An improved structure of the complex has been obtained.

The rotational spectrum of the hydrogen-bonded dimer formed between 3,3-dimethyloxetane and hydrogen chloride has been investigated in the region 6–18 GHz using a molecular-beam Fourier transform microwave spectrometer with a dual-flow injection system. A single axial conformer has been observed for the complex in the supersonic jet. A Cs-symmetry effective structure has been derived from the rotational parameters of the parent, 37Cl- and 13C-monosubstituted species in their natural abundance, with HCl forming an axial hydrogen bond to the oxygen atom of the ring of 3,3-dimethyloxetane. The non-observation of a plausible equatorial conformer is discussed.

A spectrometer that combines laser ablation of a solid sample with molecular-beam Fourier-transform microwave spectroscopy (MB-FTMW) has been constructed to obtain the rotational spectrum of solid organic molecules. Laser ablation is produced by visible radiation, using the second harmonic of a Nd:YAG laser. The laser hits a solid rod placed on a specially designed pulsed nozzle, coaxially oriented with the axis of the microwave spectrometer Fabry–Perot cavity. The vaporized molecules are seeded in the supersonic jet formed by the expansion of a carrier gas (Ar,Ne) and probed by FTMW spectroscopy. The high sensitivity of the spectrometer is exemplified with the observation of minor isotopomers in natural abundance of different organic molecules and natural amino acids. This instrument opens perspectives in the investigation of the gas phase structure of solid organic compounds.

The methylfluoroacetylenes CH3–(CC)2–F and CH3–(CC)3–F have been generated for the first time in a pulsed-discharge nozzle and characterized by molecular beam Fourier transform microwave spectroscopy in the 5–26 GHz frequency range. The spectroscopic constants B=1086.44824(13) MHz, DJ=0.02044(70) kHz, and DJK=7.083(91) kHz of CH3–(CC)2–F and B=478.908444(34) MHz, DJ=0.003060(98) kHz, and DJK=1.899(22) kHz of CH3–(CC)3–F have been determined. In addition, the 13C isotopic species of CH3–CC–F in their natural abundances have been measured, and a partial substitution structure of CH3–CC–F has been derived and compared with those of related fluorine derivatives.

The fluorobenzene–hydrogen chloride π-hydrogen-bonded complex has been studied by high resolution microwave spectroscopy and ab initio calculations. Rotational spectra of the C6H5F–H35Cl, C6H5F–H37Cl, and C6D5F–H35Cl isotopomers were assigned using pulsed molecular beam techniques in a Fourier-transform microwave spectrometer. The spectra are consistent with a structure of the complex in which the HCl is above the fluorobenzene ring near the ring center, similar to the benzene–HCl prototype dimer. An analysis of the inertial data and the chlorine quadrupole coupling tensor results in two mathematically possible locations for the HCl subunit with respect to the fluorobenzene arising from sign ambiguities in interpreting the spectral constants. One structure has the HCl nearly perpendicular to the aromatic ring; the other has the HCl pointing toward the fluorine end of the ring. Spectral intensities for the μa and μb transitions favor the former configuration. Ab initio calculations (MP2/6-311++G(2df,2pd)+B...

The nuclear quadrupole coupling hyperfine structure arising in the rotational spectra of dichlorofluoromethane and pyridazine due to the presence of two equivalent quadrupolar nuclei (Cl and N, respectively) has been investigated using molecular beam Fourier transform microwave spectroscopy in the 6–18 GHz frequency range. For dichlorofluoromethane the species CH 35 Cl 2 F, CH 35 Cl 37 ClF and CH 37 Cl 2 F have been investigated whereas for pyridazine only the parent species with two 14 N has been observed. Thanks to the sub-Doppler resolution and high sensitivity inherent to this technique, the hyperfine structure for the low J transitions has been resolved and the complete nuclear quadrupole coupling tensors have been determined. Diagonalization of the tensor for dichlorofluoromethane molecule has given interesting information which reveals very small deviations between the Cl nuclei quadrupole coupling tensors principal axes z and the ClC bonds. The experimental results have been compared with those from MP4/6-311+G(2d,2p) ab initio calculations.

Difluoromethane dimer has been generated in a supersonic beam expansion and characterised using Fourier transform microwave spectroscopy. The rotational transitions of the parent species together with the spectra corresponding to both 13C isotopomers have been measured. Spectral analysis yielded rotational and centrifugal distortion constants for the observed species. The r0 and rs hydrogen-bond structural parameters of the complex were determined from the inertial data. The derived structure is consistent with a cooperative union in the dimer formed by three hydrogen bonds.

The jet-cooled rotational spectra of the parent and three isotopic species (13CC2H6S3, C3H634SS2 and C3H633SS2) in natural abundance of 1,3,5-trithiane have been observed by laser ablation combined with molecular-beam Fourier transform microwave spectroscopy. The r0 and rs structures of the molecule have been determined from the rotational data. The sensitivity of the experimental set-up proved to be high enough to observe the 33S isotopomer in natural abundance. An analysis of the nuclear quadrupole hyperfine structure due to the 33S nucleus allowed the determination of the quadrupole coupling tensor, giving some insight about the electronic distribution around this atom.

New laboratory data of ethyl mercaptan, CH$_{3}$CH$_{2}$SH, in the millimeter and submillimeter-wave domains (up to 880 GHz) provided very precise values of the spectroscopic constants that allowed the detection of $gauche$-CH$_3$CH$_2$SH towards Orion KL. 77 unblended or slightly blended lines plus no missing transitions in the range 80-280 GHz support this identification. A detection of methyl mercaptan, CH$_{3}$SH, in the spectral survey of Orion KL is reported as well. Our column density results indicate that methyl mercaptan is $\simeq$ 5 times more abundant than ethyl mercaptan in the hot core of Orion KL., Comment: Accepted for publication in ApJL (30 January 2014)/ submitted (8 January 2014)

Producción Científica, The rotational spectra of laser ablated picolinic and isonicotinic acids have been studied using broadband chirped pulse (CP-FTMW) and narrowband molecular beam (MB-FTMW) Fourier transform microwave spectroscopies. Two conformers of picolinic acid, s-cis-I and s-cis-II, and one conformer of isonicotinic acid have been identified through the analysis of their rotational spectra. The values of the inertial defect and the quadrupole coupling constants obtained for the most stable s-cis-I conformer of picolinic acid, evidence the formation of an O–H···N hydrogen bond between the acid group and the endocyclic N atom. The stabilization provided by this hydrogen bond compensates the destabilization energy due to the adoption of a −COOH trans configuration in this conformer. Its rs structure has been derived from the rotational spectra of several 13C, 15N, and 18O species observed in their natural abundances. Mesomeric effects have been revealed by comparing the experimental values of the 14N nuclear quadrupole coupling constants in the isomeric series of picolinic, isonicotinic, and nicotinic acids., Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA175U13)

Microwave spectroscopy, considered as the most definitive gas phase structural probe, is able to distinguish between different conformational structures of a molecule, because they have unique spectroscopic constants and give rise to distinct individual rotational spectra.

The rotational spectrum of the hydrogen bond heterodimer 2,5-dihydrofuran⋯HF has been investigated in the frequency region 6–18.5 GHz using molecular beam Fourier transform microwave spectroscopy. The R-branch μa-type spectra of the parent, 2,5-dihydrofuran⋯DF, 13Cα-2,5-dihydrofuran⋯HF and 13Cβ-2,5-dihydrofuran⋯HF species have been measured. All the observed lines are split into two components due to the tunneling of HF between the two equivalent hydrogen bonding sites at the oxygen atom. A value for the barrier to HF inversion of 100 cm−1 has been calculated from the analysis of the rotational constants of both tunneling states on the basis of a simple one-dimensional model. Ab initio calculations at the MP2/6-311+G(d,p) and MP2/6-311+G(2df,p) levels of theory have been carried out to complement the experimental data. The results on the HF inversion barrier and hydrogen bond angular geometry of 2,5-dihydrofuran⋯HF have been compared to those previously obtained for the H2O⋯HF complex.

The hydrogen-bonded complex formed between 7-oxabicyclo[2.2.1]heptane and HF (OBH···HF) has been generated in a supersonic jet and characterised by Fourier transform microwave spectroscopy. The rotational transitions of the parent and C6H10O···DF species, together with the spectra corresponding to 13C monosubstituted species have been analysed. Spectral analysis yielded rotational and centrifugal distortion constants and the parameter Daa accounting for HF subunit spin (H)–spin (F) coupling. These data are consistent with Cs symmetry and a linear hydrogen bond lying in the symmetry plane bisector to the angle COC. The structure of the OBH subunit in the complex has been determined and it can be concluded that no significant structural distortion occurs upon complexation. No detectable inversion doubling attributed to the HF inversion has been observed.

The hydrogen-bonded heterodimer 7-oxabicyclo[2.2.1]heptane···HCl (OBH···HCl) has been investigated using a molecular beam Fourier-transform microwave spectrometer. The ground state rotational spectra of the OBH···H35Cl, OBH···H37Cl and OBH···D35Cl isotopomers have been studied in the frequency range 6–18.5 GHz. Spectral analysis gave rotational, quartic centrifugal distortion constants and the complete Cl-nuclear quadrupole coupling tensor for all isotopomers. A Cs symmetry has been established for the complex where the hydrogen chloride lies on the plane bisector to the COC angle of OBH. The distance r(O···H) and the angle φ between the OBH C2 axis and the O···H bond direction were found to be 1.764(29) A and 129.7(37)°, respectively. A small deviation of the linearity of the atoms O···H–Cl involved in the hydrogen bond, θ = 7(4)°, was observed. Ab initio calculations were also performed to complement the experimental work.

The rotational spectra of 1,1-dichloroethane in the ground state of the CH3CH35Cl2, CH3CH35Cl37Cl and CH3CH37Cl2 isotopomers and in four low frequency excited states of the main species have been investigated in the range 6–250 GHz. Measurements have been carried out using molecular beam and waveguide Fourier transform microwave spectrometers as well as Stark and source modulation spectrometers. Accurate rotational and centrifugal distortion constants have been obtained. The complete Cl-nuclear quadrupole coupling tensors have been determined from the analysis of the resolved hyperfine structure for the three observed isotopomers. From the small A–E splittings observed in the first torsional excited state, the barrier to internal rotation of the methyl group has been determined to be 4.260(9) kcal mol−1.

We report the assignment and analysis of all stable monosubstituted isotopomers of trifluoroacetic acid. The 13C and 18O isotopomers were observed in natural abundance. The rotational constants and quartic centrifugal constants are presented. The rotational constants are used to derive a partial substitution structure and a complete ro structure for future comparison with the corresponding values in hydrogen bridged bimolecules containing trifluoroacetic acid as a subunit. The deuterium nuclear quadrupole coupling constants are derived from the hfs-splittings of low-J rotational transitions of the CF3COOD isotopomer. The results of ab initio quantum chemical calculations are presented, which were carried out to assist in the assignment of the rotational spectra of the isotopomers and for comparison with the experimental molecular parameters.

The ground-state rotational spectrum of the tetrahydrothiophene···water complex (C4H8S···H2O) has been studied by free jet millimeter wave absorption and molecular beam Fourier transform microwave spectroscopy. The spectra of H2O and D2O combined with C4H832S and C4H834S were assigned. The rotational parameters have been interpreted in terms of a geometry in which the water molecule acts as proton donor lying close to the plane bisector to the CSC angle of tetrahydrothiophene. The “free” hydrogen is entgegen to the ring. The parameters characterizing the hydrogen bond are the distance between the sulfur and hydrogen atoms, r(S···H) = 2.37(4) A, and the angle between the line bisecting the CSC angle of tetrahydrothiophene and the S···H bond, φ = 85.(3)°. The deviation from collinearity of the atoms S···H−O is suggested from θ = 162.(12)°.

The jet-cooled rotational spectrum of the tetrahydrofuran–argon molecular complex has been investigated by millimeter-wave absorption and Fourier transform microwave spectroscopies. The argon atom is located nearly over the oxygen atom, almost perpendicularly to the COC plane. Each rotational transition is split in two component lines due to the residual pseudorotational effects of the ring in the complex. The splitting between the two vibrational sublevels has been calculated to be 111.345(44) MHz.

The ground-state rotational spectra of two isotopomers, C 4 H 8 32 S ⋯HF and C 4 H 8 34 S ⋯HF, of the tetrahydrothiophene⋯HF complex have been analyzed to give rotational constants, centrifugal distortion constants and the H,F nuclear spin–nuclear spin coupling constant D aa . These parameters are consistent with a dimer structure characterized by a distance r (S⋯F)=3.067(22) A, an angle of 88.28(29)° between the S⋯F internuclear line and the line bisecting the CSC angle and an angle of deviation of the S⋯F internuclear line from the CSC angle bisector plane of 1.64(75)°. The deviation from collinearity of the atoms S⋯H–F has been found to be θ =10.5(45)°.

The closed-shell linear chain SiCCO has been generated for the first time in a supersonic expansion by a DC electric discharge of silane, acetylene, and carbon monoxide highly diluted in neon, and it has been probed by Fourier transform microwave spectroscopy in the 5-26 GHz frequency range. The spectroscopic constants B = 2624.2202(12) MHz and DJ = 0.235(47) kHz have been determined. With these constants, the radio spectrum of SiCCO can be predicted with an accuracy better than 1 km s-1 in equivalent radial velocity up to 60 GHz.

WOS: 000317788800014, PubMed ID: 24981533, beta-aminoisobutyric acid (BAIBA) has been studied in isolation conditions: in the gas phase and trapped into a cryogenic N-2 matrix. A solid sample of the compound was vaporized by laser ablation and investigated through their rotational spectra in a supersonic expansion using two different spectroscopic techniques: broadband chirped pulse Fourier transform microwave spectroscopy and conventional molecular beam Fourier transform microwave spectroscopy. Four conformers with structures of two types could be successfully identified by comparison of the experimental rotational and N-14 nuclear quadruple coupling constants with those predicted theoretically: type A, bearing an OH center dot center dot center dot N intramolecular hydrogen bond and its carboxylic group in the trans geometry (H-O-C=O dihedral similar to 180 degrees), and type B, having an NH center dot center dot center dot O bond and the cis arrangement of the carboxylic group. These two types of conformers could also be trapped from the gas phase into a cryogenic N-2 matrix and probed by Fourier transform infrared (IR) spectroscopy. In situ irradiation of BAIBA isolated in N-2 matrix of type B conformers using near-IR radiation tuned at the frequency of the O-H stretching 1st overtone (similar to 6930 cm(-1)) of these forms allowed to selectively convert them into type A conformers and into a new type of conformers of higher energy (type D) bearing an NH center dot center dot O=C bond and a O-H "free" trans carboxylic group, COMPETE-QREN-EU [PTDC/QUI-QUI/111879/2009]; Portugal-Spain Bilateral Project [E-7 CRUP-MCI 2011-E03]; Ministerio de Ciencia y Innovacion [CTQ 2006-05981/BQU, CTQ 2010-19008]; Consolider Ingenio [CSD 2009-00038]; Junta de Castilla y Leon [VA070A08]; Spain-Portugal Bilateral Project [AIB2010PT-00315], These studies were performed under projects PTDC/QUI-QUI/111879/2009 (also funded by COMPETE-QREN-EU) and the Portugal-Spain Bilateral Project E-7 CRUP-MCI 2011-E03. This work has also been supported by the Ministerio de Ciencia y Innovacion (Grant Nos. CTQ 2006-05981/BQU and CTQ 2010-19008), Consolider Ingenio 2010 (Grant No. CSD 2009-00038), Junta de Castilla y Leon (Grant No. VA070A08), and the Spain-Portugal Bilateral Project AIB2010PT-00315.

International audience; We report on the detection of hydromagnesium isocyanide, HMgNC, in the laboratory and in the carbon rich evolved star IRC+10216. The J=1-0 and J=2-1 lines were observed in our microwave laboratory equipment in Valladolid with a spectral accuracy of 3\,KHz. The hyperfine structure produced by the Nitrogen atom was resolved for both transitions. The derived rotational constants from the laboratory data are $B_0$=5481.4333(6)\,MHz, $D_0$=2.90(8)\,KHz, and $eQq(N)$=-2.200(2)\,MHz. The predicted frequencies for the rotational transitions of HMgNC in the millimeter domain have an accuracy of 0.2-0.7\,MHz. Four rotational lines of this species, J=8-7, J=10-9, J=12-11 and J=13-12, have been detected towards IRC+10216. The differences between observed and calculated frequencies are $

The microwave spectrum of 2-chloro-1,1,1,2-tetrafluoroethane has been analyzed in the frequency region 12–52 GHz using waveguide Fourier transform and Stark modulation microwave spectrometers. The spectra of 35 Cl and 37 Cl isotopomers and of the two lowest excited states of the CF 3 torsional vibration of 35 Cl species have been measured up to J = 58. Chlorine nuclear quadrupole coupling constants have been determined from a first-order analysis of the observed hyperfine components. Rotational constants and quartic centrifugal distortion constants have been determined from the calculated central frequencies. Relative intensity measurements give a value of 4.0 ± 1.8 kcal mole −1 for the barrier to internal rotation of CF 3 group.

The molecular beam Fourier transform microwave spectrum in the ground vibrational state of the symmetric rotor CH 3 –C C–CF 3 has been detected and analyzed in the frequency interval 6–18 GHz. The molecule was generated in a pulsed dc electric discharge of trifluoropropyne and propyne seeded in neon. The observed spectrum exhibits a complex pattern of lines for each rotational transition consistent with free internal rotation of the two tops. The rotational parameters B , D J , D Jm , D JK , D JKm and H Jm have been determined from the fit of the observed lines.

A laser ablation device in combination with a molecular beam Fourier-transform microwave spectrometer has allowed the observation of the rotational spectrum of serotonin for the first time. Three conformers of the neurotransmitter have been detected and characterized in the 4-10 GHz frequency range. The complicated hyperfine structure arising from the presence of two (14)N nuclei has been fully resolved for all conformers and used for their identification. Nuclear quadrupole coupling constants of the nitrogen atom of the side chain have been used to determine the orientation of the amino group probing the existence of N-Hπ interactions involving the amino group and the pyrrole unit in the Gauche-Phenyl conformer (GPh) or the phenyl unit in the Gauche-Pyrrole (GPy) ones.

Supported by accurate quantum-chemical calculations, the rotational spectra of the mono- and bi-deuterated species of fluoroiodomethane, CHDFI and CD(2)FI, as well as of the (13)C-containing species, (13)CH(2)FI, were recorded for the first time. Three different spectrometers were employed, a Fourier-transform microwave spectrometer, a millimeter/submillimter-wave spectrometer, and a THz spectrometer, thus allowing to record a huge portion of the rotational spectrum, from 5 GHz up to 1.05 THz, and to accurately determine the ground-state rotational and centrifugal-distortion constants. Sub-Doppler measurements allowed to resolve the hyperfine structure of the rotational spectrum and to determine the complete iodine quadrupole-coupling tensor as well as the diagonal elements of the iodine spin-rotation tensor. The present investigation of rare isotopic species of CH(2)FI together with the results previously obtained for the main isotopologue [C. Puzzarini, G. Cazzoli, J. C. López, J. L. Alonso, A. Baldacci, A. Baldan, S. Stopkowicz, L. Cheng, and J. Gauss, J. Chem. Phys. 134, 174312 (2011); G. Cazzoli, A. Baldacci, A. Baldan, and C. Puzzarini, Mol. Phys. 109, 2245 (2011)] enabled us to derive a semi-experimental equilibrium structure for fluoroiodomethane by means of a least-squares fit procedure using the available experimental ground-state rotational constants together with computed vibrational corrections. Problems related to the missing isotopic substitution of fluorine and iodine were overcome thanks to the availability of an accurate theoretical equilibrium geometry (computed at the coupled-cluster singles and doubles level augmented by a perturbative treatment of triple excitations).

The rotational spectra of the 35 Cl 35 Cl, 35 Cl 37 Cl, and 37 Cl 37 Cl isotopomers of cis - 1,2-dichloroethylene have been observed in the frequency range 12.4-246 GHz. Accurate rotational constants and all the quartic and sextic centrifugal distortion constants have been obtained from semirigid rotor fits to the central line frequencies corrected for the chlorine nuclear quadrupole coupling. The chlorine nuclear quadrupole coupling constants of the 35 Cl 35 Cl, 35 Cl 37 Cl, and 37 Cl 37 Cl isotopomers have been determined.

Nicotine has been investigated in the gas phase and two conformational forms were characterized through their rotational spectra. Two spectroscopic techniques have been used to obtain the spectra: a new design of broadband Fourier transform microwave (FTMW) spectroscopy with an in-phase/quadrature- phase-modulation passage-acquired-coherence technique (IMPACT) and narrowband FTMW spectroscopy with coaxially oriented beam-resonator arrangement (COBRA). The rotational, centrifugal distortion and hyperfine quadrupole coupling constants of two conformers of nicotine have been determined and found to be in N-methyl trans configurations with the pyridine and pyrrolidine rings perpendicular to one another. The quadrupole hyperfine structure originated by two 14N nuclei has been completely resolved for both conformers and used for their unambiguous identification. © 2011 the Owner Societies.

The ground vibrational state microwave spectra of the 35 Cl and 37 Cl isotopomers of 1-cbloro-1-fluoroethylene and cis -l-chloro-2-fluoroethylene have been studied in the frequency range 26-245 GHz. Chlorine nuclear quadrupole coupling constants have been obtained from first-order analyses of the frequencies of 100 hyperfine components for each isotopomer. Rotational constants and quartic and sextic centrifugal distortion constants have been determined from fits to large numbers of central transition frequencies. A brief description of the computer-controlled source modulation millimeter-wave spectrometer used in this work is given.

The rotational spectra of both 35Cl and 37Cl 1,1-difluoro-2-chloroethylene isotopomers have been measured in the frequency range 12-225 GHz. A first order quadrupole coupling analysis has been performed for both isotopic species. The calculated quadrupole coupling constants for the 37Cl species not previously reported are χaa = - 49.2 (2), χbb = 14.2 (1), and χcc = 28.7 (1). Accurate rotational constants, quartic and some sextic centrifugal distortion constants have also been determined for both isotopomers from the fit to the observed central frequencies.

g-Aminobutyric acid (GABA) is arguably the most important inhibitory neurotransmitter in the brain and brainstem/spinal cord. Owing to the high torsional flexibility of its heavyatom backbone, this molecular system has a large number of low-energy conformers (see Figure 1). Identifying the stable conformers of GABA can be relevant to understanding the selectivity of the biological processes in which the neurotransmitter participates. This can be done by placing GABA on a supersonic jet such that conformers are cooled down and trapped in their energy minima. In such an isolated environment the conformers with sufficient population can be detected and studied by spectroscopic methods. In this context, several methods have made great contributions to the elucidation of the structures of biomolecules in the gas phase. In the present work we have observed and characterized nine conformers of GABA using Fourier transform microwave spectroscopy in supersonic jets combined with laser ablation. Microwave spectroscopy, considered the most definitive gas-phase structural probe, can distinguish between different conformational structures since they have unique moments of inertia and give separate rotational spectra. In general, large molecules, in particular those of biological importance, have low vapor pressures and tend to degrade upon heating, making them unsuited for structural studies in the gas phase. Recently, rotational studies of biomolecules have entered in a new stage with the LAMB-FTMW experiment, which combines laser ablation (LA) with molecular beam Fourier transform microwave spectroscopy (MB-FTMW), an approach that overcomes the problems of thermal decomposition associated with conventional heating methods. To date, different aand b-amino acids have been studied using this technique, making it possible to characterize their preferred conformations. Even in conformationally challenging systems these can be identified by rotational spectroscopy, as has been illustrated with the assignment of seven low-energy conformers of serine and threonine, six of cysteine, and four of b-alanine and proline. In the present work, we have examined the conformations of GABA. In this system the separation of the polar amino and carboxylic groups, characteristic of many families of neurotransmitters, opens new conformational possibilities with respect to a-amino acids if one considers the balance of intramolecular forces that contribute to stabilizing the different conformations. The five hindered rotations around the single bonds generate a plethora of conformational species (Figure 1). An overall picture of the conformational landscape obtained from theoretical predictions at the MP2/6-311++G(d,p) level confirms the conformational richness of GABA: the 30 feasible conformers shown in Figure 1 were localized with relative energies below 900 cm . These conformers are labeled by two letters (a, G, or g) followed by a number. The first letter refers to the configuration at Ca and the second one to the configuration at Cg : a means anti conformers, G gauche conformers with positive value of the torsional angle CCOOH-Ca-Cb-Cg or N-Cg-Cb-Ca, and g gauche conformers Figure 1. Predicted low-energy conformers of GABA. The nine observed conformers are circled.

The rotational spectra of both 35 Cl and 37 Cl 1,1-difluoro-2-chloroethylene isotopomers have been measured in the frequency range 12-225 GHz. A first order quadrupole coupling analysis has been performed for both isotopic species. The calculated quadrupole coupling constants for the 37 Cl species not previously reported are χ aq X= − 49.2 (2), χ bb = 14.2 (1), and χ cc = 28.7 (1). Accurate rotational constants, quartic and some sextic centrifugal distortion constants have also been determined for both isotopomers from the fit to the observed central frequencies