Hannelore I. Bloemink

Isolation of H2S…ClF in a pre-reactive mixture of H2S and ClF expanded in a coaxial jet and characterisation by rotational spectroscopy

Abstract The reaction between H 2 S and ClF was precluded and H 2 S…ClF isolated by a coaxial supersonic expansion of the gaseous components into the Fabry-Perot cavity of a pulsed-nozzle, Fourier-transform microwave spectrometer. The ground-state rotational spectra of seven isotopomers of H 2 S…ClF were analysed and gave in each case the spectroscopic constants 1 2 (B 0 + C 0 ), D J , χ aa (Cl) and M bb (Cl). Interpretation of these constants revealed the complex to have a geometry of C s symmetry with the S…ClF nuclei collinear in the order shown, with the angle 180°− φ = 84.2(4)° between the C 2 axis of H 2 S and the S…ClF axis, and with r( S…Cl ) = 2.857(3) A .

Geometry and nature of the binding of the pre-reactive complex C2H4…ClF from its rotational spectrum

Abstract The encounter complex C 2 H 4 …ClF was isolated by using a fast-mixing nozzle before chemical reaction could occur between the components and was characterised by Fourier-transform microwave spectroscopy. Rotational constants, centrifugal distortion constants, Cl nuclear quadrupole constants and Cl spin-rotation constants were determined for the isotopomers C 2 H 4 … 35 ClF and C 2 H 4 … 37 ClF. The complex has C 2v symmetry with the ClF subunit perpendicular to the plane of C 2 H 4 and oriented so that Cl is closer to C 2 H 4 . Both the centrifugal distortion constant Δ J and the Cl nuclear quadrupole coupling constants indicate that the complex is relatively weakly bound and it is concluded that the interaction between the subunits is largely electrostatic in origin.

Properties of the intermediate ethyne…Cl2 from its rotational spectrum and some generalisations for a series B…Cl2

Abstract A T-shaped planar complex of ethyne and Cl 2 has been isolated in a mixture of the substances using a pulsed-nozzle, FT microwave spectrometer and characterised through its rotational spectrum. Rotational constants ( A 0 , B 0 , C 0 ), centrifugal distortion constants (Δ J , Δ JK , δ J ), and Cl-nuclear quadrupole coupling constants χ aa (Cl) and χ bb (Cl)  χ cc (Cl) of both Cl nuclei are reported for the isotopomer (HCCH, 35 Cl 2 ). The angular geometry, electric charge redistribution within the Cl 2 subunit and intermolecular force constant k σ , as derived from the spectroscopic constants, are compared with those of other B…Cl 2 and of the corresponding series B…HCl to give some generalisations.

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.

Characterisation of a pre-reactive intermediate in gas-phase mixtures of fluorine and ammonia: the rotational spectrum of the H3N…F2 complex

Abstract A weakly bound complex of NH 3 and F 2 has been detected as a pre-reactive intermediate in mixtures of the component gases and characterised by means of its ground-state rotational spectrum. Chemical reaction of NH 3 and F 2 was precluded by using a fast-mixing nozzle in a Fourier-transform microwave spectrometer. Spectroscopic constants B 0 , D J and D JK are reported for both symmetric-top isotopomers H 3 14 N…F 2 , and the 14 N-nuclear quadrupole constant is given for the former species. The complex has a geometry H 3 N…FF of C 3v symmetry, with r( N…F ) = 2.708(7) A and the intermolecular force constant k σ = 4.69(3) N m −1 .

THE COMPLEX H3N...BR2 CHARACTERIZED IN THE GAS PHASE BY ROTATIONAL SPECTROSCOPY

The ground‐state rotational spectra of four isotopomers of the complex H3N...Br2 have been observed using pulsed‐nozzle, FT microwave spectroscopy. Reaction of NH3 and Br2 was avoided by using a fast‐mixing nozzle. The isotopomers H315N...79Br2, H315N...81Br79Br, H315N...79Br81Br, and H315N...81Br2 exhibited symmetric‐top type spectra which were analyzed to give rotational constants B0, the centrifugal distortional constants DJ and DJK, the Br‐nuclear quadrupole coupling constants χ(Brx) (x=i, inner or o, outer), and the Br spin‐rotational coupling constants Mbb (Brx). The distances r(N...Bri)=2.72(2) A and r(Br–Br)=2.335(10) A in the complex were estimated from the rotational constants while the intermolecular stretching force constant kσ=18.5(5) N m−1 was determined from DJ. An interpretation of the magnitude of the χ(Brx) values and the difference Δχ(Br)=χ(Bri)−χ(Bro) allows the conclusion that the extent of intermolecular charge transfer is probably small and that a polarization of Br2 equivalent to t...

'CHARGE-TRANSFER' COMPLEXES OF AMMONIA WITH HALOGENS : NATURE OF THE BINDING IN H3N...BRCL FROM ITS ROTATIONAL SPECTRUM

The ground-state rotational spectra of the four isotopomers H315N⋯79Br35Cl, H315N⋯81Br35Cl, H315N⋯79Br37Cl and H315N⋯81Br37Cl of a complex formed by ammonia and bromine monochloride have been observed by pulsed-nozzle, FT microwave spectroscopy. A fast-mixing nozzle was used to prevent a chemical reaction between the components and allow the encounter complex to be isolated. The nature of the spectra establishes that the observed isotopomers are symmetric-top molecules. Assignment and analysis of the spectrum in each case lead to the rotational constant Bo, the centrifugal distortion constants DJ and DJK, the halogen nuclear quadrupole coupling constants χ(Br) and χ(Cl), and the component Mbb(Br) of the bromine spin–rotation coupling tensor. The rotational constants allowed an ro-type value of the distance N⋯Br of 2.627 A to be established. An rs-type method led to the distances r(N⋯Br)= 2.59(1)A and r(Br—Cl)= 2.186 A, the former requiring a value of Bo for H314N⋯79Br35Cl obtained from unperturbed transition centres estimated without a full hyperfine structure analysis. A consideration of the intermolecular stretching force constant kσ, determined from DJ, provides evidence of a relatively strong interaction between the subunits. However, an analysis of the χ(X)(X = Br, Cl) values reveals that the molecular interaction is mainly electrostatic in origin, with probably only a small extent of intermolecular electric charge redistribution on complex formation.

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…ClF 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…ClF nuclei were established.

H2S⋯Cl2 characterised in a pre-reactive gas mixture of hydrogen sulfide and chlorine through rotational spectroscopy: the nature of the interaction

The ground-state rotational spectra of five isotopomers (H2S⋯35Cl2, H2S⋯35Cl37Cl, H2S⋯37Cl35Cl, HDS⋯35Cl2 and D2S⋯35Cl2) of a complex formed by hydrogen sulfide and chlorine have been observed with a pulsed-nozzle, Fourier-transform microwave spectrometer. The reaction of H2S and Cl2 was precluded by employing a fast-mixing nozzle. The rotational constant ½(B0+C0), the centrifugal distortion constant DJ and the Cl-nuclear quadrupole coupling constants χaa(Cli) and χaa(Cl0)(i = inner Cl atom, o = outer Cl atom) were determined in each case. The rotational constants were interpreted, under the assumption of unperturbed monomer geometries, to establish that H2S⋯Cl2 has a geometry in which the SClCl nuclei are collinear or almost collinear, with the Cl2 subunit nearly perpendicular to the plane of the H2S nuclei. The observed angular geometry is rationalised in terms of a set of rules previously used to discuss hydrogen-bonded complexes B⋯HX. The strength of the interaction, as measured by the force constant kσ(determined from DJ), and the electric charge redistribution within Cl2 on formation of H2S⋯Cl2[determined from the χaa(Clx)] both indicate that the complex is of the weak, outer type described by Mulliken. A comparison of the properties of H2S⋯Cl2 and H2S⋯HCl reveals that the complexes are similar in several respects and explanations for these similarities are given in terms of the electric charge distributions of Cl2 and HCl. In particular, the reason why the angular geometries of both can be predicted by some electrostatically based rules is discussed.

Mulliken inner complexes [(CH3)3 NCl]+...F− in pre-reactive mixtures of trimethylamine and chlorine monofluoride: identification and characterisation by rotational spectroscopy

Abstract Ground-state rotational spectra of four symmetric-top isotopomers of a pre-reactive complex formed by trimethylamine and chlorine monofluoride were observed by using a fast-mixing nozzle in a Balle-Flygare microwave spectrometer. The spectroscopic constants B 0 , D J , D JK , Ξ aa (CL), M aa ( Cl )and Tr M (Cl) were determined. The observed complex has a structure of C 3 or C 3v symmetry, with the ionic form [(CH 3 ) 3 NCl] + ...F − as the main contributor to its valence-bond description, i.e. the ion Cl + is largely transferred from ClF to N to trimethylamine on complex formation. Thus, the observed complex is of the Mulliken inner type.