Internuclear Line Research Articles

Spontaneous vacuum decay in low-energy collisions of heavy nuclei beyond the monopole approximation

The problem of spontaneous vacuum decay in low-energy collisions of heavy nuclei is considered beyond the scope of the monopole approximation. The time-dependent Dirac equation is solved in a rotating coordinate system with $z$-axis directed along the internuclear line and the origin placed at the center of mass. The probabilities of electron-positron pair creation and the positron energy spectra are calculated in the approximation neglecting the rotational coupling. The two-center potential is expanded over spherical harmonics and the convergence with respect to the number of terms in this expansion is studied. The results show that taking into account the two-center potential instead of its spherically symmetric part preserves all the signatures of the transition to the supercritical regime that have been found in the framework of the monopole approximation and even enhances some of them.

Distortion of ethyne on formation of a π complex with silver chloride: C2H2⋯Ag–Cl characterised by rotational spectroscopy and ab initio calculations

C(2)H(2)⋯Ag-Cl was formed from ethyne and AgCl in the gas phase and its rotational spectrum observed by both the chirped-pulse and Fabry-Perot cavity versions of Fourier-transform microwave spectroscopy. Reaction of laser-ablated silver metal with CCl(4) gave AgCl which then reacted with ethyne to give the complex. Ground-state rotational spectra of the six isotopologues (12)C(2)H(2)⋯(107)Ag(35)Cl, (12)C(2)H(2)⋯(109)Ag(35)Cl, (12)C(2)H(2)⋯(107)Ag(37)Cl, (12)C(2)H(2)⋯(109)Ag(37)Cl, (13)C(2)H(2)⋯(107)Ag(35)Cl, and (13)C(2)H(2)⋯(109)Ag(35)Cl were analysed to yield rotational constants A(0), B(0), and C(0), centrifugal distortion constants Δ(J), Δ(JK), and δ(J), and Cl nuclear quadrupole coupling constants χ(aa)(Cl) and χ(bb)(Cl)-χ(cc)(Cl). A less complete analysis was possible for (12)C(2)D(2)⋯(107)Ag(35)Cl and (12)C(2)D(2)⋯(109)Ag(35)Cl. Observed principal moments of inertia were interpreted in terms of a planar, T-shaped geometry of C(2v) symmetry in which the AgCl molecule lies along a C(2) axis of ethyne and the Ag atom forms a bond to the midpoint (∗) of the ethyne π bond. r(0) and r(m)(1) geometries and an almost complete r(s)-geometry were established. The ethyne molecule distorts on complex formation by lengthening of the C≡C bond and movement of the two H atoms away from the C≡C internuclear line and the Ag atom. The r(m)(1) bond lengths and angles are as follows: r(∗⋯Ag) = 2.1800(3) Å, r(C-C) = 1.2220(20) Å, r(Ag-Cl) = 2.2658(3) Å and the angle H-C≡∗ has the value 187.79(1)°. Ab initio calculations at the coupled-cluster singles and doubles level of theory with a perturbative treatment of triples (F12∗)∕cc-pVTZ yield a r(e) geometry in excellent agreement with the experimental r(m)(1) version, including the ethyne angular distortion.

The rotational spectrum of thiophene⋯HBr and a comparison of the geometries of the complexes B⋯HX, where B is benzene, furan or thiophene and X is F, Cl or Br

The ground-state rotational spectra of three isotopomers C4H4S⋯H79Br, C4H4S⋯H81Br and C4H4S⋯D79Br of a weakly bound complex formed by thiophene and hydrogen bromide have been observed in the gas phase by means of a pulsed-jet, Fourier-transform instrument. Each spectrum was analysed and fitted to give rotational constants A0, B0 and C0, centrifugal distortion constants ΔJ, ΔJK, ΔK, δJ and δJK and the components χaa, χbb − χcc and χab of the bromine nuclear quadrupole coupling tensor. A detailed analysis of the spectroscopic constants established that the geometry of the complex is of the face-on type. The Br atom of HBr is located close to the perpendicular drawn through the centre of mass of the thiophene ring and the H atom of HBr lies between the Br atom and the ring. The angle αaz made by the HBr internuclear axis z with the a-axis has the two possible values ±9.83°. The preferred structure is that generated when the positive value of the angle is chosen and has the HBr sub-unit pointing in the direction of the S atom of thiophene. The determined geometrical parameters are r(S⋯H) = 2.728(3) A, ϕ = 116.0(2)° and θ = 7.08(4)°, where ϕ is the angle made by the S⋯H internuclear line with the local C2 axis of thiophene and θ is the angular deviation of the S⋯H–Br nuclei from collinearity.

Rotational spectroscopy of a weak complex of thiirane and ethyne: The identification and properties of a highly nonlinear S⋯H–C hydrogen bond

Rotational and centrifugal distortion constants were determined for eight isotopomers of a weakly bound complex of thiirane and ethyne. The observed complex is of Cs symmetry, with ethyne lying in the symmetry (ab principal inertial) plane and with H of HCCH forming a hydrogen bond to the S atom of thiirane. The r0 geometry is: r(S⋯H)=2.76(5) Å, φ=84.0(5)°, and θ=42.9(2)°, where φ is the angle made by the S⋯H internuclear line with the local C2 axis of the thiirane ring and θ is the angular deviation of the S⋯H–C nuclei from a linear arrangement. The nonlinearity of the hydrogen bond is attributed to a weak primary interaction S⋯H–C coupled with a secondary interaction involving the π bond of ethyne with the two equivalent H atoms of thiirane that are closest to it. The angular geometry of (CH2)2S⋯HCCH is compared with those of other species (CH2)2S⋯HX, where X=F, Cl, Br, and CN.

Understanding the Hydrogen Bond in Terms of the Location of the Bond Critical Point and the Geometry of the Lone Pairs

The experimental charge density method has been employed to provide a more detailed description of the hydrogen bond in terms of the location of the bond critical point and the geometry of the lone pair of electrons. On the basis of a study of 7 different O−H···O hydrogen-bonded systems with 19 hydrogen bonds covering a wide range of hydrogen bond distances and angles, it has been possible to arrive at a generalization of the topological descriptors. In all of the hydrogen bonds studied, the electron density at the bond critical point (BCP) and its Laplacian fall in the range of 0.03−0.39 eÅ-3 and 0.7−6.0 eÅ-5, respectively. The bond paths deviate, in some instances widely, from the H···O bond axis, and the resulting dCP values (vertical displacement of the bond critical point from the internuclear line) range from 0.036 to 0.418 Å. The origin of such high dCP values has been related to the constellation of the various interaction centersthe lone pairs and the atom cores of the donor and the acceptor oxygens and the hydrogen atom. This study provides a useful classification of the hydrogen bonds in terms of a new interaction line, Li-j, connecting the various centers i and j. A nearness parameter, dL, that represents the perpendicular distance of the critical point from the interaction line, Li-j, justifies the classification. The dL values are found to be much smaller than the corresponding dCP values.

Non-linearity of weak B⋯H–C hydrogen bonds: an investigation of a complex of vinyl fluoride and ethyne by rotational spectroscopy

Rotational and centrifugal distortion constants were determined for seven isotopomers of a weakly bound complex of vinyl fluoride and ethyne. The complex is planar or nearly planar, with a H of HCCH forming a hydrogen bond to the F atom of vinyl fluoride. The r 0 geometry is: r(F⋯H)=2.441(4) Å, φ=122.7(4)° and θ=36.5(2)°, where φ is the angle made by the F⋯H internuclear line with the C–F internuclear axis and θ is the angular deviation of the F⋯H–C nuclei from collinearity. The non-linearity θ is attributed to the effect of a secondary interaction involving the π-bond of ethyne with one of the H atoms on C 2 of vinyl fluoride. The angular geometry of C 2H 3F⋯HCCH is compared with those of other species C 2H 3F⋯HX.

Are members of the family of hydrogen-bonded complexes formed by furan with the hydrogen halides isostructural? An answer from the rotational spectrum of furan⋯HBr

The ground-state rotational spectra of the five isotopomers C4H4O⋯H79Br, C4H4O⋯H81Br, C4D4O⋯H79Br, C4H4O⋯D79Br, and C4H4O⋯D81Br of a weakly bound complex formed by furan with hydrogen bromide in the gas phase have been observed with a pulsed-jet, Fourier-transform instrument. Each spectrum was analyzed and fitted to give rotational constants A0, B0, and C0, centrifugal distortion constants ΔJ and ΔJK, and components χaa, χbb-χcc, and χab (or χac in the case of C4D4O⋯H79Br) of the bromine nuclear quadrupole coupling tensor. A detailed analysis of the spectroscopic constants reveals that the observed complex does not have C2v symmetry, with HBr lying along the C2 axis of furan. Instead, the geometry is of the face-on type, with the Br atom of HBr lying close to the perpendicular drawn through the center of the mass of the furan ring. The H atom of HBr lies between the Br atom and the face of the furan ring. The angles αaz made by the HBr internuclear axis z with the a axis has the two possible values ±11.929°. The preferred structure is that generated when the positive value of the angle is chosen and has the HBr subunit pointing in the direction of the O atom of furan. The determined geometrical parameters are r(O⋯H)=2.599(3) Å, φ=112.90(14)°, and θ=6.05(4)°, where φ is the angle made by the O⋯H internuclear line with the local C2 axis of furan and θ is the angular deviation of the O⋯H–Br nuclei from collinearity. Reasons why furan⋯HCl, but not furan⋯HBr, obeys some simple rules for predicting angular geometries are discussed.

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.

Interaction of water and dichlorine in the gas phase: An investigation of H2O⋯Cl2 by rotational spectroscopy and ab initio calculations

Ground-state rotational spectra of the seven isotopomers H2O⋯35Cl2, H2O⋯37Cl35Cl, H2O⋯35Cl37Cl, D2O⋯35Cl2, D2O⋯37Cl35Cl, HDO⋯35Cl2, and HDO⋯37Cl35Cl of the complex formed between water and dichlorine were observed by pulsed-jet, Fourier-transform microwave spectroscopy. Rotational constants B0 and C0, centrifugal distortion constants ΔJ and ΔJK, and Cl nuclear quadrupole coupling constants χaa(Clx) and {χbb(Clx)−χcc(Clx)}, where x=i (inner) or o (outer), were obtained via spectral analyses. The spectroscopic constants were interpreted, on the basis of models for the complex, to give the geometry, the binding strength, and the extent of inter- and intramolecular electron transfer on complex formation. The zero-point geometry is defined in terms of the effective values r(O⋯Cli)=2.8479(3) Å and φ=43.4(3)°, where φ is the angle made by the bisector of the HÔH angle with the O⋯Cl internuclear line. The intermolecular stretching force constant kσ=8.0(1) N m−1. Fractions δi=0.005(5) and δp=0.034(3) of an electron were estimated to be transferred from O to Cl and from Cli to Clo, respectively. The geometrical conclusions are supported by ab initio calculations at the aug-cc-pVDZ/MP2 level of theory, with good agreement for φ and r(O⋯Cli). A comparison of the properties of H2O⋯Cl2 with those of H2O⋯HCl provides evidence in support of a recent proposal of a halogen bond B⋯XY that is the analog of the hydrogen bond B⋯HX, where X and Y are halogen atoms.

Rotational spectrum and structure of the tetrahydrothiophene⋯hydrogen fluoride complex

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) Å, 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)°.

Observation and Properties of the Hydrogen-Bonded Heterodimer Tetrahydrothiophene···HCl

The ground-state rotational spectra of five isotopic species, C4H832S···H35Cl, C4H832S···H37Cl, C4H832S··· D35Cl, C4H832S···D37Cl, and C4H834S···H35Cl, of a hydrogen-bonded dimer between tetrahydrothiophene and hydrogen chloride have been measured in the frequency range 6−18.5 GHz using a molecular beam Fourier transform microwave spectrometer. Spectral analysis gave rotational, quartic centrifugal distortion and Cl−nuclear quadrupole coupling constants for each isotopomer. The rotational and quadrupole coupling constants have been interpreted in terms of a geometry in which hydrogen chloride lies on the plane bisector to the CSC angle of tetrahydrothiophene. The angle between the S···Cl internuclear line and the line bisecting the CSC angle was found to be 86.6(7)° and the distance r(S···Cl) = 3.48(3) Å. The deviation of the atoms S···H−Cl involved in the hydrogen bond from a collinear arrangement (θ = 0°) was estimated to be θ ∼ 14°.

Rotational spectrum of thiophene···HCl Does thiophene act as an aromatic π-type electron donor or an n-type electron donor in hydrogen-bond formation?

The rotational spectra of the four isotopomers [32S]-thiophene···H35Cl, [32S]-thiophene···H37Cl, [32S]-thiophene···D35Cl and [34S]-thiophene···H35Cl of a complex formed between thiophene and hydrogen chloride have been observed by using a pulsed-nozzle, Fourier-transform microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl-nuclear quadrupole coupling constants χaa, χbb-χcc and χab were determined. Interpretation of the spectroscopic constants led to the conclusion that the observed complex has Cs symmetry, with the Cl atom of HCl lying almost directly above the centre of mass of the thiophene ring but with the H atom of HCl pointing at the π-electron density near to the S atom. The S···H–Cl nuclei are almost collinear [ϑ=0.9(6)°] but the relatively large distance r(S···H)=2.7474(29) A indicates that the S···H interaction is weak. The angle φ between the C2 axis of thiophene and the S···H internuclear line was found to be 64.53(16)°. The distance r(*···Cl)=3.693 A from the centre of mass (*) of the thiophene ring to Cl and the angle (S*Cl)=98.9° are very similar in magnitude to the corresponding quantities in thiophene···Ar. Indeed, a comparison of thiophene···Ar, thiophene···HCl, benzene···Ar and benzene···HCl revealed a strong family relationship between the geometries of these four complexes. It is concluded that the non-bonding electron pair carried by S in thiophene is so weakly nucleophilic that when thiophene forms a hydrogen bond with HCl it does so via the aromatic π-electron system. In this respect, thiophene resembles benzene and is in stark contrast to its oxygen analogue, furan, with which HCl forms a hydrogen-bonded complex of C2v symmetry via the non-bonding electron pair on O.

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) Å, 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 geometries of several complexes B⋯XY, where B is 2,5-dihydrofuran, oxirane, or formaldehyde, and XY is ClF or HCl, is discussed. It is shown that for a given B the angle 180-φ is the same for XY=HCl or ClF, while the nonlinearity θ of the O⋯X–Y system is almost negligible for XY is ClF but significant when XY is HCl. Reasons for this family relationship and the nonlinear O⋯H–Cl hydrogen bonds are discussed.

The rotational spectrum of the complex 2,5-dihydrofuran···HBr and the non-linearity of the O···HνBr hydrogen bond

S. A. Cooke, G. K. Corlett, C. M. Evans and A. C. Legon, J. Chem. Soc., Faraday Trans., 1997, 93, 2973 DOI: 10.1039/A702576I

Floquet analysis of inelastic collisions of ions with Rydberg atoms.

The theory of Demkov et al. (Zh. Eksp. Teor. Fiz. 66, 125 (1974) [Sov. Phys. JETP 39, 57 (1974)]) for collisional mixing of degenerate states of a hydrogenlike target is generalized to nonhydrogenic targets parametrized by a set of quantum defects, {${\mathrm{\ensuremath{\mu}}}_{\mathit{l}}$}, with l the orbital angular-momentum quantum number of the Rydberg electron. Schr\"odinger's equation is written in periodic form in the impact-parameter approximation by using the angle of rotation of the internuclear line, as opposed to the time, as the independent variable. Quasiperiodic solutions are constructed by Floquet analysis, as in studies of Rydberg-state mixing by oscillatory fields, leading to an infinite-dimensional eigenvalue equation whose eigenvectors and eigenvalues determine the evolution operator of the collision system. An initial application to ``l-mixing collisions'' of ions with alkali-metal atoms indicates that dipole-forbidden transitions dominate depopulation cross sections at intermediate collision speeds.

Rotational spectrum of a short-lived dimer of oxirane and hydrogen chloride: Evidence for a bent hydrogen bond

Ground state rotational spectra of the three isotopomers (CH2)2O...H35Cl, (CH2)2O...H37Cl, and (CH2)2O...D35Cl of a short-lived hydrogen-bonded dimer have been detected in the reactive mixture of oxirane and hydrogen chloride by using a fast-mixing nozzle in conjunction with a Balle–Flygare Fourier-transform microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl-nuclear quadrupole coupling constants were determined for each isotopomer. In particular, all four components χaa, χbb, χcc, and χac of the coupling tensor were obtained. A detailed analysis of the rotational constants allows the conclusion that the dimer has Cs symmetry, with a steeply pyramidal arrangement completed at oxygen by the hydrogen bond with HCl. Diagonalization of the complete Cl-nuclear quadrupole coupling tensor leads to the principal axis components χxx, χyy, and χzz (where z is the HCl direction in the dimer). The angle of rotation α is the angle between the HCl (z) direction and the a-axis direction in the equilibrium conformation of the dimer. It is larger by ∼10° than the angle γ between the O...Cl internuclear line and the principal inertial axis a in each case and implies that the hydrogen bond is bent by 180-θ=∼16.5° from the collinear arrangement O...H–Cl (θ=0). The angle 180-θ and the angle φ=76.2° made by the O...Cl internuclear line with the extension of the oxirane local C2 axis are interpreted in terms of a simple model of the hydrogen bond.

ChemInform Abstract: Microwave Spectrum, rs Structure, Dipole Moment, and Nuclear Quadrupole Coupling Constant Tensor of Ethyl Bromide.

Abstract Microwave spectra of ethyl iodide and its six isotopic species have been measured. A least-squares analysis of the observed frequencies gave rotational, quartic centrifugal distortion constants and the components of the nuclear quadrupole coupling constant tensor for all the seven isotopic species. The rs structure has been well established from the moments of inertia calculated from the observed rotational constants. The observed nuclear quadrupole coupling constant tensor in the inertial principal axes system could be transformed into that in its own principal axes system which gave the following conclusions. The tensor is roughly cylindrically symmetric around the z axis which is slightly deviated by about 56′ from the CI internuclear line. From the Stark effect measurements of several low J transitions for the three isotopic species, the dipole moments have been determined. For the normal species, μa = 1.884(3) D, μb = 0.598(10) D, and μtotal = 1.976(5) D and the dipole moment makes an angle of 2°9′ with the CI bond.

Microwave spectrum, rs structure, dipole moment, and nuclear quadrupole coupling constant tensor of ethyl bromide

Microwave spectra of ethyl bromide and its 13 isotopic species have been measured. A least-squares analysis of the observed frequencies gave rotational, quartic centrifugal distortion constants and components of the nuclear quadrupole coupling constant tensor. The rs structure has been well established from the observed moments of inertia. The nuclear quadrupole coupling constant tensor in the inertial principal axes system obtained from the spectra could be transformed into that in its own principal axes system which gave the following conclusion. The tensor is roughly cylindrically symmetric around the z axis which is slightly shifted by 50′ from the CBr internuclear line. From the Stark effect measurements of several low J transitions for the three isotopic species, the dipole moment has been determined. For the normal species, μa = 1.951(16), μb = 0.596(12), and μtotal = 2.040(19)D and the dipole moment makes an angle of 5°22′ with the CBr bond inclining its positive pole toward the methyl group.

Microwave spectrum, rs structure, dipole moment, and nuclear quadrupole coupling constant tensor of ethyl lodide

Microwave spectra of ethyl iodide and its six isotopic species have been measured. A least-squares analysis of the observed frequencies gave rotational, quartic centrifugal distortion constants and the components of the nuclear quadrupole coupling constant tensor for all the seven isotopic species. The r s structure has been well established from the moments of inertia calculated from the observed rotational constants. The observed nuclear quadrupole coupling constant tensor in the inertial principal axes system could be transformed into that in its own principal axes system which gave the following conclusions. The tensor is roughly cylindrically symmetric around the z axis which is slightly deviated by about 56′ from the CI internuclear line. From the Stark effect measurements of several low J transitions for the three isotopic species, the dipole moments have been determined. For the normal species, μ a = 1.884(3) D, μ b = 0.598(10) D, and μ total = 1.976(5) D and the dipole moment makes an angle of 2°9′ with the CI bond.

Quasimolecular or kinematical broadening of autoionization electron spectra from Li+/He collisions? a coincidence study

We have measured energy- and angular distributions of autoionization electrons from Li+/He collisions in coincidence with the scattered Li+ projectiles. The coincident energy spectra do not exhibit the broad structures that are observed in the non coincident spectra and which in the past were attributed to quasimolecular autoionization of the (LiHe)+ system. We show that these broad structures are caused by kinematical shifts of electron spectra from pure atomic autoionization following different scattering events. With an exploitation of published inelastic differential scattering cross sections and with the assumption that the angular electron distribution with respect to the asymptotic internuclear line is nearly independent of the scattering angle we are able to reproduce the non coincident electron spectra satisfactorily.