C.M. Evans

Is the gas-phase complex of ammonia and chlorine monofluoride H3N…ClF or [H3NCl]+…F−? Evidence from rotational spectroscopy

Abstract Ground-state rotational spectra of the symmetric-topic isotopomers H 3 14 N… 35 ClF, H 3 14 N… 37 ClF, H 3 15 N… 35 ClF and H 3 15 N… 37 ClF of the ammonia-chlorine monoffluoride complex were observed with a fast-mixing nozzle/F-T microwave spectrometer combination. The determied spectroscopic constants B 0 , D J , D JK , χ aa (Cl), M aa (Cl) and Tr M (Cl) allow the conclusion that the complex has a C 3v geometry with nuclei in the order H 3 N…ClF and a relatively strong intermolecular bond ( k σ = 34.3(6) N m −1 ). Comparison of both χ aa (Cl) and k σ for the series B…Cl 2 and B…ClF (B = CO, HCN and NH 3 ) suggests a small contribution of the ionic structure [H 3 NCl] + …F − in the valence-bond description of H 3 N…ClF.

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 .

The rotational spectrum of the benzene hydrogen bromide complex

Abstract Ground-state rotational spectra of six symmetric-top isotopomers, C 6 H 6 ⋯ H 79 Br, C 6 H 6 ⋯ H 81 Br, C 6 D 6 ⋯ H 79 Br, C 6 D 6 ⋯ H 81 Br, C 6 H 6 ⋯ D 79 Br and C 6 H 6 ⋯ D 81 Br, of the benzene-hydrogen bromide complex were observed and analysed to give the rotational constant B 0 , the centrifugal distortion constants D J and D JK , and the Br nuclear quadrupole and spin-rotation coupling constants X aa and M bb in each case. It is concluded that in the zero-point state the complex has effective C 6v symmetry, with HBr oriented so that H lies closest to the benzene ring and undergoes a circular motion which allows it to sample the π-electron density of the ring.

Are B…ClF bonds linear? The angular geometry of a pre-reactive complex of oxirane and chlorine monofluoride from rotational spectroscopy

Abstract A pre-reactive complex formed by oxirane and ClF was characterised through the ground-state rotational spectra of the isotopomers (CH 2 ) 2 O… 35 ClF and (CH 2 ) 2 O… 37 ClF. The complex has C s symmetry, with the O…Clue5f8F nuclei confined to the symmetry ( ac ) plane. Determination of the complete Cl nuclear quadrupole coupling tensor χ aa , χ bb - χ cc and χ ac led to the equilibrium angle α az between the ClF axis ( z ) and the a -axis directions. By fitting the observed rotational constants A 0 , B 0 and C 0 under the assumption of unchanged monomer geometries and with α az fixe the geometrical parameters r( O…Cl ) = 2.437(2) A , f = 112.7(1)° and the deviation θ = 2.91(3)° from collinearity of the O…Clue5f8F nuclei were established.

Angular geometries of complexes containing the O⋯Cl–F linkage: Rotational spectrum of formaldehyde⋯chlorine monofluoride

Ground-state rotational spectra of the three isotopomers H2CO⋯35ClF, H2CO⋯37ClF and D2CO⋯35ClF of a complex formed by formaldehyde and chlorine monofluoride were observed with a Balle–Flygare, Fourier-transform microwave spectrometer. A fast-mixing nozzle, specially modified to generate a continuous supply of H2CO from paraformaldehyde in situ close to the nozzle exit, was used to preclude the chemical reaction of H2CO and ClF. The rotational constants A0, B0, and C0, centrifugal distortion constants ΔJ, ΔJK, and δJ, components χaa, χbb−χcc, χab of the Cl-nuclear quadrupole tensor, and the spin–rotation coupling constant 1/2(Mbb+Mcc) were determined. Interpretation of the spectroscopic constants led to the conclusion that H2CO⋯ClF is a planar complex of Cs symmetry with r(O⋯Cl)=2.523(7)u2009A, with an angle 180−φ=69.1(7)° between the C2 axis of H2CO and the O⋯Cl internuclear line, but with a deviation θ of the O⋯Cl–F nuclei from collinearity of only 3.2(7)°. A family relationship between the angular geometrie...

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.

Nature and angular geometry of the pre-reactive complex thiirane-chlorine monofluoride from its rotational spectrum

Abstract The rotational spectrum of the pre-reactive complex thiirane-ClF was detected with a fast-mixing nozzle in an FT microwave spectrometer. Rotational constants, centrifugal distortion constants, Cl-nuclear quadrupole and spin-rotation coupling constants were determined for the isotopomers (CH 2 ) 2 S… 35 ClF and (CH 2 ) 2 S… 37 ClF. The complex has C s symmetry, with a nearly collinear arrangement of the S…Clue5f8F nuclei ( σ ≈3.5°) and the Clue5f8F axis making an angle φ =95° with the C 2 axis of thiirane. The Cl-nuclear quadrupole coupling constant χ zz along the ClF internuclear axis suggests a significant contribution of the ionic structure [(CH 2 ) 2 SCl] + …F − to a valence-bond description of the complex.

Rotational spectrum and angular geometry of a pre-reactive complex of oxirane and F2

Abstract Rotational spectra of two isotopomers, (CH 2 ) 2 O … F 2 and (CD 2 ) 2 O … F 2 , of a pre-reactive complex of oxirane and F 2 were observed with a Balle-Flygare microwave spectrometer. Chemical reaction between the components was avoided by use of a fast-mixing nozzle. Rotational ( A 0 , B 0 , C 0 ) and centrifugal distortion ( Δ J , Δ JK , δ K ) constants were determined for each isotopomer. The complex has an angular geometry isomorphous with those of oxirane … HCl and oxirane … ClF, with φ = 98(6)°, the O … Fue5f8F noncollinear by at most 10° and r( O … F ) = 2.69(6) A . A comparison of oxirane … F 2 and oxirane … Ar reveals similarities understandable in terms of the F 2 electric charge distribution.

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.

Configuration at oxygen and deviation of the O…ClF system from linearity in 2,5-dihydrofuran…ClF from rotational spectroscopy

Abstract Rotational spectra of two isotopomers of the 2,5-dihydrofuran/ClF complex were observed by using the fast-mixing nozzle/Balle-Flygare spectrometer combination. The complex has C s symmetry and a pyramidal configuration at oxygen. The angle between the 35 ClF axis ( z ) and the a -axis, α az = 17.95(3)°, was determined from the Cl nuclear quadrupole coupling tensor. The geometry r( O … Cl ) = 2.422(5) A , θ = 127.0(3)° and θ = 1.99(15)° is established when rotational constants are fitted under the constraints of unperturbed monomers and α az = 17.95(3)°. the configurations θ at O and the nonlinearities θ of the B…ClF/B…HCl systems are compared for B = 2,5-dihydrofuran and oxirane.