Internuclear Line Research Articles

Photon emission spectroscopy of highly charged ions following low energy charge exchange collisions

The theory of charge exchange is discussed in the framework of the quasi-molecular model. The classical one electron model indicates a specific state population. The Landau-Zener model is applied to charge exchange collision, two specific interaction appear : (a) radial coupling induced by the radial motion, (b) excitation effect due to rotational motion of the internuclear line during a collision. An example of n,1 distribution is given through the multi-channel Landau-Zener theory. The various radiative processes resulting from initial alignment suggest that polarization measurements make possible the differentiation of radial and rotational coupling.

Angular correlation between autoionisation electrons from Ne(2p43s2)1D and scattered ions in He++Ne collisions

Angular distributions of autoionisation electrons from Ne(2p43s2)1D due to He++Ne collisions at 2 keV were measured in coincidence with the scattered projectiles and compared with those of electrons from He(2p2)1D, measured by Kessel et al. (1979). A theoretical analysis of such angular electron correlations in terms of a density-matrix description is given. The authors find that the Ne excitation occurs in a nearly pure m=0 sublevel with respect to an axis in the scattering plane which coincides with the internuclear line of the collision partners on the outgoing part of the trajectory at a separation of R approximately=2.4a0. This is interpreted as being due to an excitation at small R by a radial coupling of two Sigma -potential curves, followed by a rotation of the quasimolecule as a whole up to R approximately=2.4a0. A quantitative estimate of the energy separations between Sigma , Pi and Delta potential curves correlating to He++Ne(2p43s2)1D indicates that a rotational coupling between these curves is responsible for the decoupling of electronic and nuclear motion at R approximately 2.4a0.

Molecular-Dipole Deformation as a Collective Variable in Charge-Changing Ion-Atom Collisions

The molecular dipole moment along the internuclear line is treated as a collective coordinate to describe the sharing of electrons in slow atomic collisions. With use of the constrained Hartree-Fock method, potential energy surfaces for Li-F and ${(\mathrm{H}\mathrm{e}\ensuremath{-}\mathrm{H}\mathrm{e})}^{2+}$ are calculated as a function of the internuclear separation and the dipole deformation. This offers a conceptual framework to view a charge-changing process as the motion along a path in the energy surface. Consequences for the molecular orbitals are discussed.

A new method for observing the rotational spectra of weak molecular complexes: KrHCl

A new method of observing the rotational transitions of weak molecular complexes by combining the techniques of microwave Fourier transform spectroscopy, a Fabry–Perot cavity, and a pulsed nozzle source of molecules is described. High resolution and good sensitivity are achieved. Twelve isotopic species of the KrHCl molecule involving all combinations of the 86Kr, 84Kr, 82Kr, H, D, 35Cl, and 37Cl isotopes are assigned and the rotational constants, Cl nuclear quadrupole coupling constants, and centrifugal distortion constants are all given. The molecular structure indicates a linear equilibrium structure with the H(D) atom between the Kr and Cl atoms. However, the inverse moments of inertia measured here indicate large amplitude vibrations of the H(D) atom relative to the Kr–Cl internuclear line. Estimates of the Kr–Cl stretching frequency and force constants, which show considerable dependence on the isotopic species, are also given. Bending frequencies and force constants are also given.

Molecular-orbital approach to ion-atom collisions with multiply charged projectiles

In a slow collision between a multiply charged projectile ion and a neutral target atom, self-consistent molecular orbitals in the entrance channel can be defined by introducing a variational constraint which enforces the initial charge sharing and reflects the charge-equilibration process during the collision. In the present work, the interaction of an auxiliary electric field with the electronic dipole moment along the internuclear line is added to an effective single-electron Hamiltonian in order to simulate a constrained Hartree-Fock procedure. In this way, correlation diagrams for the systems ${\mathrm{N}}^{2+}$ + O and ${\mathrm{Ne}}^{4+}$ + Ne are computed. The diagrams exhibit crossings between energy curves of like symmetry. The correlations are found to be the same as in the corresponding charge-balanced (or neutral) systems and are hence consistent with existing experimental data.

Angular correlation between autoionization electrons and scattered ions in 2000-eVHe+-He collisions

Complex population amplitudes for the excitation of magnetic sublevels of $\mathrm{He}(2{p}^{2})^{1}D$ and $\mathrm{He}(2s2p)^{1}P$ states in 2-keV ${\mathrm{He}}^{+}$ -He collisions have been determined by measuring the energy spectra of the corresponding autoionization electrons ejected at different angles in coincidence with the inelastically scattered ions. It was found that $\mathrm{He}(2{p}^{2})^{1}D$ is excited with a relative probability of 97%. If the direction of the internuclear line at the distance of closest approach is taken as $z$ axis, we find that primarily the $m=0$ sublevel is populated and that the complete $^{1}D$ excitation can be interpreted as due to pure $m=0$ excitations with respect to momentary internuclear lines at different points of the trajectory which are symmetric to the turning point. These results are discussed within the framework of the Fano-Lichten promotion model. Quantization along an axis perpendicular to the scattering plane shows an orientation of the excited $^{1}D$ state. From this we find that the angular momentum ${L}_{y}$ transferred from the motion of the heavy particles to the electron cloud has an expectation value of $〈{L}_{y}〉\ensuremath{\approx}\ensuremath{-}\ensuremath{\hbar}$.

Configuration interaction studies of the HeH+ molecular ion. I Singlet sigma states

The method of superposition of configurations is applied to the singlet sigma states of HeH+ which correlate to the separated atom states of principal quantum number less than or equal to 3. The calculations are carried out for internuclear separations in the ranges 0(.1)34.5, 35.0(.5)50.0 bohr. Energy eigenvalues and the expectation values of the electron coordinate along the internuclear line are discussed in this paper. Dipole transition matrix elements and radial coupling matrix elements are presented in a companion paper. The quality of the calculations is exhibited by comparisons of the length and velocity forms of the dipole matrix elements, by the Hellmann-Feynman theorem, and by the approach to atomic properties at large internuclear separations. Supplementary calculations of higher quality wavefunctions for the lowest states are also reported. These are used to help estimate the extent to which the results of the main calculations have converged toward the exact values. Comparisons with other work are given. It is shown that for internuclear separations greater than about 3 bohr a one-electron electron model potential approach is quite successful for the excited states. At smaller internuclear separations, and as the united atom limit is approached, current model potential methods cannot be trusted. In this region the model potential, being based on the separated atoms, cannot describe the actual changing charge distributions of the core electron. This work demonstrates the feasibility, for simple systems, of the ab initio structure calculations required for the quantitative description of low-energy atom-atom collisions.

ChemInform Abstract: THE MICROWAVE SPECTRUM AND QUADRUPOLE COUPLING CONSTANT TENSOR OF BROMOMETHYLSILANE

Chemischer InformationsdienstVolume 4, Issue 50 Organoelement Compounds ChemInform Abstract: THE MICROWAVE SPECTRUM AND QUADRUPOLE COUPLING CONSTANT TENSOR OF BROMOMETHYLSILANE MICHIRO HAYASHI, MICHIRO HAYASHISearch for more papers by this authorKAZUNORI KUWADA, KAZUNORI KUWADASearch for more papers by this author MICHIRO HAYASHI, MICHIRO HAYASHISearch for more papers by this authorKAZUNORI KUWADA, KAZUNORI KUWADASearch for more papers by this author First published: December 11, 1973 https://doi.org/10.1002/chin.197350372AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume4, Issue50December 11, 1973 RelatedInformation

The Microwave Spectrum and Quadrupole Coupling Constant Tensor of Bromomethylsilane

Abstract The microwave spectra of four isotopic species of bromomethylsilane have been measured, viz., the 79Br and 81Br species of BrCH2SiH3 and BrCH2SiD3. The observed rotational constants have been well explained by a model of which the structural parameters have been transferred from the corresponding parameters determined for ethylbromide and chloromethylsilane. The principal quadrupole coupling constants have been determined through the analysis of the first- and second-order effects of quadrupole coupling on the hyperfine structure of the observed spectra. It was concluded, within the experimental error, that the quadrupole coupling constants tensor of this molecule has the cylindrical symmetry around the largest principal axis, the direction of which coincides approximately with the C–Br internuclear line.

Microwave spectrum, barrier to internal rotation, structure, and dipole moment of methane selenol

The microwave spectra of the ground state and excited torsional states of several isotopic species of methane selenol have been observed. The barrier hindering internal torsion has been determined to be 1001±50 cal/mole. The structural parameters are C–Se= 1.959 Å, Se–H= 1.473 Å, C–H= 1.088 Å, ∠C–Se–H= 95.45°, ∠H–C–H= 110.00°, with the symmetry axis of the methyl group tilted 1.5° away from the C–Se internuclear line. The dipole moment components are μA=1.253 D, μB=0.314 D, μtotal=1.291 D. The implications of this barrier height determination for theories on the orgin of the barrier are discussed.

Rotationally Induced Transitions in Atomic Collisions

Excitation effects due to rotational motion of the internuclear line during an atomic collision are considered in the two-state approximation. These effects are governed by a pair of first-order differential equations which couple adiabatic levels of different angular momentum (e.g., $\ensuremath{\sigma}$ to $\ensuremath{\pi}$ transitions), which actually do cross. The equations are cast in such a form that the solution for rotational excitation may be expressed in terms of the well-known Landau-Zener solution. It is found, however, that application of these results to a real collision suffers from defects which are worse for the case of rotational excitation than for ordinary Landau-Zenner transitions. The coupled differential equations are then solved numerically to document the shortcomings of the Landau-Zener approach to a real collision and to present cross-section results which are free from these defects.

Microwave Spectrum, Molecular Structure, and Bromine Nuclear Quadrupole Coupling Tensor of Bromodiborane

The rotational spectra of eight isotopic species of bromodiborane (11B2H579Br, 11B2H581Br, 10B2H579Br, 10B2H581Br, 10B11BH581Br, 11B10BH581Br, 11B2D579Br, and 11B2D581Br) were studied in the region 10–27 GHz, and analyzed to obtain values for the rotational constants and the complete bromine nuclear quadrupole coupling tensor. Structural parameters found by isotopic substitution are B–B = 1.773 ± 0.003 Å, B–Br = 1.930 ± 0.005 Å, ∢B–B–Br = 121.4 ± 0.3°. The aplanarity, with estimated correction for inertial defect, yields the bridge proton–proton distance, Hb–Hb = 1.992 ± 0.026 Å. Compari on of the structural parameters with those for diborane indicates that the bridge dimensions are affected negligibly by substitution of Br for terminal H. The nonvanishing bromine nuclear quadrupole coupling tensor elements for 79Br in 10B2H5Br are, in megahertz, χaa = 288.87 ± 0.15, χbb = − 150.96 ± 0.30, χcc = − 137.9 ± 0.36, χab = − 198 ± 9. The major principal axis of this tensor makes an angle 1.1 ± 1.0° with the B–Br internuclear line. The significant asymmetry of the tensor about the B–Br bond axis (Γ = − 0.24 ± 0.02) corresponds to an electron defect of 0.08 electron in the bromine pπ orbital normal to the molecular symmetry plane. The electric dipole component μa, determined from Stark splittings for 11B2H5Br, is 1.16 ± 0.03 D.

Microwave Spectrum, Structure, and Quadrupole Coupling Constants of Spiropentyl Chloride

The microwave spectra of C5H735Cl and C5H737Cl have been observed and analyzed. If the spiropentane ring is assumed to be in the D2d configuration, with methylene-group parameters similar to cyclopropyl chloride, the following parameters are calculated from the observed moments of inertia: r(CCl)=1.74 Å, r(CC)=1.51 Å, and ∠RCCl=118°. The quadrupole coupling constants in the inertial axis system have been obtained for both isotopic species. For the 35Cl species, the values are χaa=−30.98 MHz, χbb=6.22 MHz, and χcc=24.76 MHz. Evidence is presented which indicates that the chemical bond linking the chlorine to the ring is not axially symmetric and does not lie along the C–Cl internuclear line.

Microwave Spectrum, Quadrupole Coupling Constants, and Heavy-Atom Geometry of 2-Bromopropane

The microwave spectra of (CH3)2CH79Br, (CH3)2CH81Br, (CH3)213CH79Br, and 13CH3CH79BrCH3 have been examined, and the coordinates of the Br and C atoms have been obtained by the substitution method. The resulting bond distances and bond angles are as follows: r(CBr) = 1.957 Å, r(CC) = 1.508 Å, ∠CCBr = 110.0°, and ∠CCC = 114.2°. The quadrupole coupling constants of (CH3)2CH79Br have been determined to be χaa = 479.5 Mc/sec, χbb = −264.9 Mc/sec, and χcc = −214.6 Mc/sec. Second-order perturbation corrections were included in the analysis of the hyperfine splittings. The quadrupole coupling constants are consistent with χzz = 529.8 Mc/sec, assuming a cylindrical charge distribution, and with χzz = 514.2 Mc/sec, ηbond = 0.0303, assuming that the z axis and the CBr internuclear line coincide.

Microwave Spectrum, Molecular Structure, and Quadrupole Coupling Constants of 2-Chloropropane

The microwave spectra of (CH3)2CHCl35, (CH3)2CHCl37, (CH3)2CDCl35, (CH3)2C13HCl35, C13H3CHCl35CH3, CH2DCl35CH3 (3 species), and CD3CDCl35CH3 have been examined and a complete structure has been obtained by the substitution method. The parameters obtained are as follows: r(CC) = 1.522 Å, r(CCl) = 1.798 Å, r(CHsec) = 1.091 Å, r(CHmethyl) = 1.092 Å, ∠CCC = 112.7°, ∠CCCl = 109.4°, ∠CCHsec = 109.9°, ∠CCHα = 110.9°, ∠CCHβ,γ = 109.7°. The quadrupole coupling constants in the principal axis system of (CH3)2CHCl35 have been determined to be χaa = —61.49 Mc/sec, χbb = 34.81 Mc/sec, and χcc = 26.68 Mc/sec. These values are consistent with χzz = —69.61 Mc/sec assuming a cylindrical charge distribution near the Cl nucleus, or with χzz = —67.82 Mc/sec and η = 0.0275 assuming that the z axis and the CCl internuclear line coincide. From the absence of observable splitting in certain high J transitions in CD3CDCl35CH3, it has been concluded that the potential barrier hindering internal rotation of the methyl groups is greater than 3450 cal/mole.

Molecular Structure of Cyclopropyl Chloride

The pure rotational microwave spectra of seven isotopic species of cyclopropyl chloride have been examined and rotational constants assigned. The data are sufficient for a complete structure determination by the substitution method. The bond distances and bond angles obtained are r(C1C2)=1.513 Å, r(C2C3)=1.515 Å, r(CCl)=1.740 Å, average r(CH)=1.08 Å, ∠CCCl=118.7°, ∠ClCH=115.8°, and ∠HCH=116.2°. The quadrupole coupling constants of C3H5Cl35 in the principal inertial axis system are χaa=—56.64 Mc/sec, χbb=36.72 Mc/sec, and χcc=19.92 Mc/sec. These values are consistent with χzz=—71.4 Mc/sec, and ηbond=0.029 if the z axis and the CCl internuclear line are assumed to coincide, and with χzz=—73.5 Mc/sec if the charge distribution near the chlorine nucleus is assumed to be cylindrically symmetric.

Antiferromagnetic and Crystal Structure of Lithium Cupric Chloride Dihydrate

A neutron-diffraction study of LiCuCl3·2H2O in the temperature range 1.4°—5.1°K, together with a magnetic susceptibility study in the range 1.4°—300°K, has determined its magnetic and crystal structure. The crystal contains linear Li–Cu–Cu–Li, planar Li2Cu2Cl6 groups. Each cation is at the center of a distorted octahedron, of composition LiCl3O3 and CuCl5O: the four octahedra share Cl–Cl edges. The most important distances in this complex are Cu–Cl at 2.25, 2.34, and 2.96 Å; Cu–O at 2.56 Å; Li–O at 2.04 and 2.18 Å; Li–Cl at 2.44 and 2.97 Å; Li–Cu at 3.34 Å; and Cu–Cu at 3.47 Å. The ``nonbridging'' Cl atoms in the Li2Cu2Cl6 group form OH···Cl bonds of 3.17 and 3.26 Å to other complexes in the crystal. The spins (S = ½) on the Cu2+ within each complex are antiparallel and lie on the 3.47-Å Cu–Cu internuclear line. The spin-density maximum is displaced 0.15 Å from the nearest neighbor Cu2+ of opposite spin. The neutron-scattering data indicates dx2—y2 to be the ground-state orbital. Above a critical field Hc = 9kOe, spin flopping similar to that in CuCl2·2H2O takes place.

Microwave Spectrum, Structure, and Quadrupole Coupling Constant Tensor of Ethyl Bromide

The microwave spectra of 10 isotopic species of ethyl bromide have been measured and assigned, viz., the 79Br and 81Br species of CH3CH2Br, CH3CD2Br, CD3CH2Br, CH313CH2Br, and 13CH3CH2Br. The spectra reported lie in the region of 18 to 31 kMc. The complete structure has been determined by the substitution method, giving the following bond parameters: CC = 1.518 Å, CBr = 1.950 Å, CCBr = 111°2′, CH (methylene) = 1.087 Å, HCH (methylene) = 109°54′, CCH (methylene) = 112°15′, HCBr = 105°25′, CH (methyl) = 1.093 Å, and HCH (methyl) = 108°52′. The principal quadrupole coupling parameters have been determined to be χzz = 541 Mc, χxx = —267 Mc, and χyy = —274 Mc for C2H579Br and χzz = 450 Mc, χxx = —220 Mc, and χyy = —230 Mc for C2H581Br. Through the analysis of second-order effects of quadrupole coupling on hyperfine structure, it was determined that, within experimental error, the CBr internuclear line and the ``z'' principal quadrupole axis coincide, indicating that the CBr bond is not bent. The barrier to internal rotation, recalculated using Lide's splitting measurements, and the above structure is 3684 cal/mole.

Microwave Spectra and Structure of Dimethyl Ether

The microwave spectra of six isotopic species of dimethyl ether were investigated from 8–48 Gc. From the changes in moments of inertia with C13 and O18 substitutions the CO distance and <COC were found to be 1.410±0.003 Å and 111°43′±20′, respectively. The conformation of the methyl groups was determined from the (CH2D) (CH3)O species. Dimethyl ether has C2v symmetry and the methyl groups are staggered with respect to the opposite CO bonds. The data from deuterium substitutions could only be satisfactorily fit by a structure containing asymmetric methyl groups. The two CH distances in this structure differ by 0.009 Å, the < HCH by 49′, and the angle between the CO internuclear line and a perpendicular to its respective hydrogen plane is 2°31′±40′. If an average CH distance of 1.0956 Å is assumed the average <HCH is 109°29′. The structure of the asymmetric methyl groups is shown to be consistent with s and p hybridization of the carbon orbitals. In this scheme the carbons form ``bent bonds'' with the oxygen. From the Stark effect the dipole moment of dimethyl ether was determined to be 1.31±0.01×10—18 esu.

Microwave Spectrum, Structure, Quadrupole Interaction, Dipole Moment, and Bent C–Cl Bonds in 1,1-dichlorocyclopropane

The microwave spectrum of C3H4Cl235,35, C3H4Cl235,37, C3D4Cl235,35 C3D4Cl235,37, C3H3DCl235,35, C3H3DCl235,37 (cis and trans), and C2C13H4Cl235,35 have been investigated. Using the derived rotational constants, a complete structure for the molecule is calculated. The structural parameters are dC–H=1.085 A, dC(2)–C(3)=1.534 A, dC(1)–C(2)=1.532 A, dC–Cl=1.734 A, ∠H–C–H=117°35′, ∠C(2)–C(3)–H2=153°37′±15′, ∠Cl–C–Cl=114°38′. κ for C2C13H4Cl235,35 was very close to zero (±0.0001), and it was not possible to determine its sign unambiguously. Using the negative value instead of the more likely positive value, a slightly different structure was obtained. High-resolution measurements were carried out on the Cl nuclear quadrupole hyperfine structure in order to obtain the complete quadrupole coupling constant tensor in the C3H4Cl235,35 principal inertial axis system. The values obtained are χaa=—43.545 Mc, χbb=4.100 Mc, χcc=39.445 Mc, all ±0.005 and χab=—51.5±0.3 Mc. The principal quadrupole-coupling constant tensor elements are χα=—76.4±0.3 Mc, χβ=37.0±0.3 Mc, and χcc=39.445±0.005 Mc. The angle between the principal quadrupole axis component along the C–Cl bond and the C–Cl internuclear line is 0±15′. This is strong evidence against bent C–Cl bonds in this compound. Detailed analysis of the Stark effect in the presence of quadrupole interaction leads to a dipole moment of 1.58 debye.