Gina Cotti

Pre-reactive complexes in mixtures of water vapour with halogens: characterisation of H2O...ClF and H2O...F2 by a combination of rotational spectroscopy and ab initio calculations.

Complexes H2O...ClF and H2O...F2 were detected by means of their ground-state rotational spectra in mixtures of water vapour with chlorine monofluoride and difluorine, respectively. A fast-mixing nozzle was used in conjunction with a pulsed-jet, Fourier-transform microwave spectrometer to preclude the vigorous chemical reaction that these dihalogen species undergo with water. The ground-state spectra of seven isotopomers (H2 16O...35ClF, H2 16O...ClF, H2 18O...35ClF, D2 16O... 35ClF, D2 16O...37ClF, HDO...35ClF and HDO...37ClF) of the ClF complex and five isotopomers (H2O...F2, H2 18O...F2, D2O...F2, D2 18O...Fi and HDO...F2) of the F2 complex were analysed to yield rotational constants, quartic centrifugal distortion constants and nuclear hyperfine coupling constants. These spectroscopic constants were interpreted with the aid of simple models of the complexes to give effective geometries and intermolecular stretching force constants. Isotopic substitution showed that in each complex the H2O molecule acts as the electron donor and either CIF or F2 acts as the electron acceptor, with nuclei in the order H2O...ClF or H2O...F2. For H2O...ClF, the angle phi between the bisector of the HOH angle and the O...Cl internuclear line has the value 58.9(16)degrees, while the distance r(O...Cl)= 2.6081(23) A. The corresponding quantities for H2O...F2 are phi = 48.5(21)degrees and r(O...Fi) = 2.7480(27) A, where Fi indicates the inner F atom. The potential energy V(phi) as a function of the angle phi was obtained from ab initio calculations at the aug-cc-pVDZ/MP2 level of theory for each complex by carrying out geometry optimisations at fixed values of phi in the range +/-80degrees. The global minimum corresponded to a complex of Cs symmetry with a pyramidal configuration at O in each. The function V(phi) was of the double-minimum type in each case with equilibrium values phie = +/-55.8degrees and +/-40.5degrees for H2O...ClF and H2O...F2, respectively. The barrier at the planar C2v conformation was V0= 174cm(-1) for H2O...ClF and 7cm(-1) for H2O...F2. For the latter complex, the zero-point energy level lies above the top of the barrier.

Rotational spectroscopy of a pre-reactive mixture of H2S and F2: detection and characterisation of the weakly bound complex H2S…F2

Abstract The rotational spectrum of a complex H 2 S…F 2 was observed in a pre-reactive mixture of hydrogen sulphide and molecular fluorine by using a fast-mixing nozzle in a Balle-Flygare microwave spectrometer. Rotational constants 1 2 (B + C) and centrifugal distortion constants Δ J were determined for the ground state and a low-lying vibrationally excited state with ν = 1 of the isotopomers H 2 S…F 2 , HDS…F 2 and D 2 S…F 2 . The vibrational satellite is probably associated with internal rotation of H 2 S about its local C 2 axis. The complex is weakly bound (intermolecular stretching force constant k σ = 2.36 N m −1 ) and has a pyramidal configuration at S, with φ = 113(5)° and r(S…F) = 3.20(1) A .

Rotational spectrum and properties of a gas-phase complex of molecular fluorine and hydrogen cyanide

Abstract Ground-state rotational spectra of three isotopomers HC14N … F2, HC15N … F2 and DC14N … F2 of a complex formed by hydrogen cyanide and molecular fluorine were observed by using a fast-mixing nozzle in a Fourier transform microwave spectrometer. Effects of F-F spin-spin and F-spin rotation coupling were observed in the spectra of HC15N … F2 and HC14N … F2 and allowed for in the analysis. Spectroscopic constants B0, DJ and ξaa(14N) appropriate to a linear molecule HCN … F2 were determined and interpreted in terms of the geometry and binding strength of the complex. Properties of several axially symmetric complexe involving the N … X2 weak bond (X = F or Cl) are compared.

Rotational spectrum and molecular properties of the dinitrogen–chlorine monofluoride complex

The ground-state rotational spectra of the three isotopomers 14N2⋯35ClF, 15N2⋯35ClF and 15N2⋯37ClF of a complex formed by dinitrogen and chlorine monofluoride have been observed with a pulsed-nozzle, Fourier-transform microwave spectrometer. The spectroscopic constants B0, DJ, χaa(A)(A =14Ni, 14No or Cl) and Mbb(Cl) are reported. The complex is shown to have a linear (or nearly linear) arrangement NoNi⋯ClF of the nuclei in the equilibrium conformation with r(Ni⋯Cl)= 2.920(2)A. The intermolecular stretching force constant, kσ= 5.00(5) N m–1, is implied by the centrifugal distortion constant DJ. Interpretation of the nuclear quadrupole coupling constants χaa(A) leads to the oscillation angles θav= cos–1〈cos2θ〉1/2= 17.8(5)° and ϕav= cos–1〈cos2θ〉1/2= 10(3)° for the N2 and ClF subunits, respectively. Additionally, the diffence χaa(Ni)–χaa(No) leads, on the basis of a simple model, to the conclusion that the polarisation of N2 attending complex formation is equivalent to the transfer of a fraction δ≈ 0.02 of an electronic charge from No to Ni. A comparison of the properties of four related complexes N2⋯YF and OC⋯YF, where Y = Cl or H, is presented.

A complex of molecular fluorine with an organic compound detected in the gas phase: the rotational spectrum of CH3CN … F2

Abstract A complex of methyl cyanide and molecular fluorine was detected by using a fast-mixing nozzle in a Fourier-transform microwave spectrometer. Ground-state rotational spectra of three symmetric-top isotopomers CH3C14N … F2, CD3C14N … F2 and CH3C15N … F2 were analysed to give the spectroscopic constants B0, DJ, DJK, HJK and χ aa ( 14 N ) . Interpretation of the spectroscopic constants revealed that the order of the nuclei on the molecular symmetry axis is C-C≡N … F-F, that r( N … F i ) = 2.748(3) A and that the complex is weakly bound as judged by the value of the intermolecular stretching force constant kσ = 2.5 N m−1 and the bending force constant kθ = 4 × 10−21 J rad−2.

Molecular geometry of SO2…ClF from its rotational spectrum: a cis, planar complex with a linear O…ClF bond

Abstract The ground-state rotational spectra of SO2…35ClF and O2…37ClF were observed by using a fast-mixing nozzle/pulsed Fourier transform microwave spectrometer combination. Rotational constants, centrifugal distortion constants and the complete Cl-nuclear quadrupole coupling tensor were determined in each case. Interpretation of the spectroscopic constants shows that the complex has a planar geometry with ClF forming a weak bond to one of the O atoms of SO2 [ r( O … Cl ) = 2.733(11) A ] in a cis arrangement with respect to the SO double bond [φ = 228.4(6)°]. The O…ClF nuclei deviate from collinearity by only θ = −0.7(2)°.