Internal rotation and molecular structure of ethaneselenol by microwave spectroscopy

The microwave spectra of ethaneselenol and its deuterated and ¹³C-substituted species were measured and assigned for the gauche and trans isomers. The double minimum splittings in the gauche isomers were directly observed for the species having a symmetry plane in the frame part. The rotational constants and the torsional splitting of the gauche isomer of the parent species were determined to be A = 27 148.86 ± 0.05, B = 3 623.68 ± 0.01, C = 3 399.21 ± 0.03, and Δν = 1 083.33 ± 0.04 MHz. From the torsional splittings of the parent and SeD species together with the vibrational frequencies already reported by Durig and Bucy, the Fourier coefficients of the selenol internal rotation potential function were determined to be V₁ = ?44 ± 17, V₂ = ?260 ± 3, V₃ = 1202 ± 16, and V₆ = ?43 ± 9 cal/mole. From the rotational constants obtained, the r_s structural parameters of the gauche and trans isomers were determined. The structural parameters in the skeletal part for the gauche isomer are $\text{r}\text{(CC) = 1.524}\text{A}\text{?}$, $\text{r}\text{(CSe) = 1.957}\text{A}\text{?}$, $\text{r}\text{(SeH) = 1.467}\text{A}\text{?}$, α(CCSe) = 113°31′, α(CSeH) = 93°05′, and the dihedral angle τ(CCSeH) = 61°39′. Those for the trans isomer are $\text{r}\text{(CC) = 1.525}\text{A}\text{?}$, $\text{r}\text{(CSe) = 1.962}\text{A}\text{?}$, $\text{r}\text{(SeH) = 1.440}\text{A}\text{?}$, α(CCSe) = 108°43′, and α(CSeH) = 93°30′. These parameters were compared with the corresponding ones of ethanethiol.     

Physical adsorption for non-planar geometries

We propose an approximation V_a(r) for the Van der Waals interaction V(r) between an atom and a non-planar solid. V_a(r) is both simpler to compute than V(r) and of considerably more convenient form. The approximation is found to be quite good except for very large z (the atom-surface separation). In the latter case, our comparison of V_a and V permits one to estimate corrections to V_a.     

The microwave spectrum,substitution structure and dipole moment of cyanobutadiyne,HCCCCCN

Cyanobutadiyne (cyanodiacetylene), HCCCCCN, is sufficiently stable at low pressures to permit its rotational spectrum to be studied by microwave spectroscopy. The spectrum consists of a series of R-branch transitions typical of a linear molecule. The transitions with J = 9 to 14 which lie between 26.5 and 40.0 GHz have been measured for the vibrational ground state. Transitions have also been detected in natural abundance for all possible singly substituted ¹³C and ¹⁵N isotopic species. Deuteriated cyanobutadiyne, DCCCCCN, has also been synthesized and its ground state spectrum recorded. These measurements have enabled a complete substitution structure to be derived for the first time for a polyacetylene: r₈(HC_a) = 1.0569 ± 0.001, r₈(C_aC_b) = 1.2087 ± 0.001, r₈(C_bC_c) = 1.3623 ± 0.003, r₈(C_cC_d) = 1.2223 ± 0.004, r₈(C_dC_e) = 1.3636 ± 0.003, $\text{r}{}_8\text{(}\text{C}{}_{\mathrm{e}}\text{}\text{N}\text{) = 1.1606 ± 0.001}\text{A}\text{?}\text{(10}{}^{\mathrm{?10}}\text{m}\text{)}$. The spectroscopic parameters for the ground state are B₀ = 1331.3313 ± 0.001 MHz and D₀ = 0.0257 ± 0.002 KHz. The dipole moment, determined from the Stark effects of the J = 9 and 10 lines, is 4.33 ± 0.03 Debye.     

Internal hydrogen bond,torsional motion,and molecular properties of 2-methoxyethylamine by microwave spectroscopy: Methyl barrier to internal rotation for 2-methoxyethanol

The microwave spectra of four substituted isotopic species of 2-methoxyethylamine (NH₂, NHD, NDH, ND₂) have been assigned. The molecule is found to exist in a gauche form with an intramolecular hydrogen bond of the NH?O type. The four possible sets of the amino hydrogen r_s corrdinates give different H?H distances, probably because the -NH₂ group is involved in large amplitude vibrations and because of changes in the heavy atom positions arising from the deuteration of the hydrogen bond. For the most abundant species many vibrational states have been analyzed and assigned to the two possible CO torsions in the molecule. A value V₃ = 3150 ± 50 cal/mol was found for the methyl torsional barrier and V₁ = 9 ± 3 kcal/mol for the other CO torsional barrier. A third set of observed vibrational satellites is probably assignable to the CC torsion. The determination of the dipole moment and of the quadrupole coupling constants gave values which were not in good agreement with those predicted from nonhydrogen bonded molecules. In addition a value V₃ = 3100 ± 100 cal/mol was calculated for the CH₃ torsional barrier in the related 2-methoxyethanol, using previous experimental data (Canad. J. Chem.50, 1149–1156 (1972)).     

The Ruderman-Kittel-Kasuya-Yosida interaction in amorphous La80Au20 alloys with dilute Gd impurities

From magnetization measurements on some amorphous dilute La_80?xGd_xAu₂₀ alloys with x ? 1 we have shown that the magnetic behavior follows the scaling laws of a spin-glass system, characteristic of the 1/r³ dependence of the pairwise interaction. We have also determined the strength of the Ruderman-Kittel-Kasuya-Yosida interaction V(r) = (V₀cos 2k_Fr)/r³, to be V₀ = 0.20 × 10^?37 ergcm³. The corresponding value of the s-f exchange integral is |J_sf| = 0.14 eV, which is compared with values determined from other experiments.     

Interaction between a He atom and a graphite surface

A study is presented of the interaction V(r) between a He atom and a graphite surface. V(r) is assumed equal to a sum of pair interactions U(r ? R_i) between the He and C atoms. None of a set of isotropic potentials (dependent only on the magnitude ¦r ? R_i¦) is consistent with recent scattering data. Anisotropie pair potentials, in contrast, are found to yield good agreement. The origin of this anisotropy is analyzed in terms of the graphite dielectric function and charge density.     

Approach to saturation of the magnetization of dilute AuFe alloys

We present a reinterpretation of our recent measurements of the magnetic properties of some dilute AuFe alloys. We find that the observed approach to saturation of the magnetization for these AuFe alloys can be understood if both single-impurity (Kondo) effects and effects due to interactions between impurities via the Rudeman-Kittel-Kasuya-Yosida (RKKY) interaction, V(r) = (V₀ cos 2k_Fr)/r³, are properly included in the analysis. The analysis yields for the strength of the RKKY interaction V₀ = (1.1 ± 0.3) × 10^-36ergcm³, for the s-d exchange parameter |J| = (1.9 ± 0.3) eV, and for the Kondo temperature T_K = (0.8 ± 0.1) K. We conclude that mean free path effects do not significantly influence the observed approach to saturation of the magnetization for the AuFe alloys studied.     

A theorem on the order of levels in confining potentials

We prove that in a two-body, non-relativistic system interacting via a potential V = ?g²/r + V_c(r), where V_c is a confining potential non-singular at the origin, the 2S level is above the 2P level if V_c satisfies the following sufficient condition: This covers the well-known cases of linear potentials or harmonic oscillator potentials, which were considered in charmonium models, but also more generally, for instance, V_c(r) = r^α, α >0.     

The inner charge defect method as an analog to the quantum defect method

A method is proposed for the calculation of one-electron wave functions for excited bound and free atomic states. For the interaction potential between the outer electron and the atomic core, we have adopted the following potential: V(r) = q₀/r for r < r₀ and V(r) = -1/r for r > r₀, where r₀ is approximately equal to the core radius, q₀(∈, 1) = Δq + 1, and Δq > 0 is the inner charge defect. It is shown, for atomic argon, that the method has about the same accuracy as those of Bates and Damgard and Brugess and Seaton.     

Observation of new nuclides37Si,40P,41S,42S produced in deeply inelastic reactions induced by40Ar on238U

A non-relativistic quantum-mechanical system is studied which consists ofN identical bosons interacting by pair potentials of the form 〈r¦V¦r ¹〉=?π/2ν ₀ a ^?3 f(r/a)f ^*(r ¹/a). General upper and lower bounds to the ground-state energyE _N are provided for alla, V ₀ andN, and detailed results are given in the case of the Yamaguchi potential for whichf(x)=e ^?x/x. It is shown that the ratioE _N /E ₂ diverges both under the limit (i) a↓0,E ₂ =arbitrary constant <0, and (ii) (V ₀ a ²)↓(V ₀ a ²)_c, where (V ₀ a ²) _c corresponds toE ₂=0. The results complement recent studies of the Efimov effect via scattering theory.     

Rotational spectrum of sulfuryl bromide fluoride

The rotational spectra of SO₂⁷⁹BrF and SO₂⁸¹BrF have been obtained between 18 and 40 GHz. Both molecules are near-prolate symmetric rotors with a and b-type dipole components. A least-squares fit of the observed moments of inertia obtained by correcting for the bromine quadrupole interaction yields $\text{r}\text{(SBr) = 2.155 ± 0.006}\text{A}\text{?}$ and ? FSBr=100.6°±1.5° structural parameters when $\text{r}\text{(SO) = 1.407}\text{A}\text{?}$, $\text{r}\text{(SF) = 1.56}\text{A}\text{?}$, and ? OSO=123.7° are assumed.     

Variation of RKKY interaction strength in dilute AuFe alloys

From measurements of the magnetic properties of some dilute AuFe alloys we find that V₀, the strength of the Ruderman-Kittel-Kasuya-Yosida interaction, V(r) = (V₀ cos 2k_Fr)/r³, decreases rapidly from V₀ = 11.9 × 10^-36 erg cm³ at n = 42 ppm Fe to 1.03 × 10^-36 erg cm³ at 6050 ppm Fe. We suggest that the observed decrease of V₀ is due to self-damping of the RKKY oscillations, and discuss the significance of this decrease for the interpretation of other experiments on AuFe.     

Simple microscopic model for the scalar-isoscalar component of the Landau-Migdal amplitude

A simple microscopic model is proposed that describes the coordinate dependence of the zeroth harmonic f ₀(r) of the scalar-isoscalar component of the Landau-Migdal amplitude. In the theory of finite Fermi systems due to Migdal, such a dependence was introduced phenomenologically. The model presented in this study is based on a previous analysis of the Brueckner G matrix for a planar slab of nuclear matter; it expresses the function f ₀(r) in terms of the off-mass-shell T matrix for free nucleon-nucleon scattering. The result involves the T matrix taken at the negative energy value equal to the doubled chemical potential μ of the nucleus being considered. The amplitude f ₀(r) found in this way is substituted into the condition that, in the theory of finite Fermi systems, ensures consistency of the self-energy operator, effective quasiparticle interaction, and the density distribution. The calculated isoscalar component of the mean nuclear field V(r) agrees fairly well with a phenomenological nuclear potential. Owing to a strong E dependence of the T matrix at low energies, the potential-well depth V(0) depends sharply on μ, increasing as |μ| is reduced. This effect must additionally stabilize nuclei near the nucleon drip line, where μ vanishes.     

Supplementing liquid-crystal NMR data with data from electron diffraction and rovibrational spectroscopy to determine a more precise and accurate structure for p-dichlorobenzene

The supplementation of data from liquid-crystal NMR with data from electron diffraction and rovibrational spectroscopy in order to determine a more precise and accurate structure and the application of this technique to p-dichlorobenzene are described. Direct and indirect couplings involving ¹³C nuclei, a rotation constant obtained by high-resolution FT IR spectroscopy, and new electron diffraction data have been recorded and analyzed simultaneously. Assuming planarity and D_2h symmetry, the best (r_α structure for p-dichlorobenzene thus obtained is rCH = 107.6(3) pm, rCC1 = 172.93(14) pm, rC(1)C(2) = 139.53(7) pm, rC(2)C(3) = 139.12(17) pm, <C(6)C(I)C(2) = 121.06(14)°, and <C(1 )C(2)H = 120.48(3)°.     

Microwave spectra of deuterated ethylenes: Dipole moment and rz structure

The pure rotational spectra of three deuterated ethylenes, CH₂CD₂, CH₂CHD, and cis-CHDCHD, were observed by microwave spectroscopy, and the rotational and centrifugal distortion constants were determined precisely. The dipole moment of CH₂CD₂ was calculated from the Stark effects to be 0.0091 ± 0.0004 D. From the observed rotational constants the average structure was calculated to be $\text{r}{}_{\mathrm{z}}\text{(CC)}\text{= 1.3391 ± 0.0013}\text{A}\text{?}$, $\text{r}{}_{\mathrm{z}}\text{(CH)}\text{= 1.0869 ± 0.0013}\text{A}\text{?}$, θ_z(CCH) = 121.28 ± 0.10°, and $\text{r}{}_{\mathrm{z}}\text{(CH)}\text{- r}{}_{\mathrm{z}}\text{(CD)}\text{= 0.00137 ± 0.00037}\text{A}\text{?}$, where the errors include one standard deviation in the fitting and errors due to an uncertainty (±0.03°) in θ_z(CCH) - θ_z(CCD).     

Atom-phonon interaction at a surface

The interaction between an atom and a phonon is evaluated at a surface. The basic assumption is that the total potential energy of the atom V(r) can be written as the sum of pair interactions w(r?r_i with individual substrate atoms. The result is an expansion in phonon wavevector q, with coefficients expressed in terms of the equilibrium adsorption potential. The coupling can be utilized in calculations of kinetic and equilibrium properties of adsorbed atoms.     

Extrapolation from positive to negative energy of the Woods-Saxon parametrization of the n-208Pb mean field

The real part V(r); E) of the nucleon-nucleus mean field is assumed to have a Woods-Saxon shape, and accordingly to be fully specified by three quantities: the potential depth U_v(E), radius R_V(E) and diffuseness a_v(E). At a given nucleon energy E these parameters can be determined from three different radial moments [r^q]_v = (4π/A) ∝V(r; E)r^q dr. This is useful because a dispersion relation approach has recently been developed for extrapolating [r^q]_V(E) from positive to negative energy, using as inputs the radial moments of the real and imaginary parts of empirical optical-model potentials V(r; E) + iW(r; E). In the present work, the values of U_v(E), R_v(E) and a_v(E) are calculated in the case of neutrons in ²⁰⁸Pb in the energy domain −20 < E < 40 MeV from the values of [r^q]_V(E) for q = 0.8, 2 and 4. It is found that both U_V(E) and R_v(E) have a characteristic energy dependence. The energy dependence of the diffuseness a_a(E) is less reliably predicted by the method. The radius R_V(E) increases when E decreases from 40 to 5 MeV. This behaviour is in agreement with empirical evidence. In the energy domain −10 MeV < E < 0, R_V(E) is predicted to decrease with decreasing energy. The energy dependence of the root mean square radius is similar to that of R_V(E). The potential depth U_v slightly increases when E decreases from 40 to 15 MeV and slightly decreases between 10 and 5 MeV; it is consequently approximately constant in the energy domain 5 < E < 20 MeV, in keeping with empirical evidence. The depth U_v increases linearly with decreasing E in the domain −10 MeV < E < 0. These features are shown to persist when one modifies the detailed input of the calculation, namely the empirical values of [r^q]_v(E) for E > 0 and the parametrization [r_q]_w(E) of the energy dependence of the radial moments of the imaginary part of the empirical optical-model potentials. In the energy domain −10 MeV < E < 0, the calculated V(r; E) yields good agreement with the experimental single-particle energies; the model thus accurately predicts the shell-model potential (E < 0) from the extrapolation of the optical-model potential (E > 0). In the dispersion relation approach, the real part V(r; E) is the sum of a Hartree-Fock type contribution V_HF(r; E) and of a dispersive contribution ΔV(r; E). The latter is due to the excitation of the ²⁰⁸Pb core. The dispersion relation approach enables the calculation of the radial moment [r^q]_ΔV(E) from the parametrization [r^q]_w(E): several schematic models are considered which yield algebraic expressions for [r^q]_ΔV(E). The radial moments [r^q]_HF(E) are approximated by linear functions of E. When in addition, it is assumed that V_HF(r; E) has a Woods-Saxon radial shape, the energy dependence of its potential parameters (U_HF, R_HF, a_HF) can be calculated. Furthermore, the values of ΔV(r; E) can then be derived. It turns out that ΔV(r; E) is peaked at the nuclear surface near the Fermi energy and acquires a Woods-Saxon type shape when the energy increases, in keeping with previous qualitative estimates. It is responsible for the peculiar energy dependence of R_V(E) in the vicinity of the Fermi energy.     

Coupled matter-wave solitons in optical lattices

We make use of a potential model to study the dynamics of two coupled matter-wave or Bose-Einstein condensate (BEC) solitons loaded in optical lattices. With separate attention to linear and nonlinear lattices we find some remarkable differences for response of the system to effects of these lattices. As opposed to the case of linear optical lattice (LOL), the nonlinear lattice (NOL) can be used to control the mutual interaction between the two solitons. For a given lattice wave number k, the effective potentials in which the two solitons move are such that the well (V_eff(NOL)), resulting from the juxtaposition of soliton interaction and nonlinear lattice potential, is deeper than the corresponding well V_eff(LOL). But these effective potentials have opposite k dependence in the sense that the depth of V_eff(LOL) increases as k increases and that of V_eff(NOL) decreases for higher k values. We verify that the effectiveness of optical lattices to regulate the motion of the coupled solitons depends sensitively on the initial locations of the motionless solitons as well as values of the lattice wave number. For both LOL and NOL the two solitons meet each other due to mutual interaction if their initial locations are taken within the potential wells with the difference that the solitons in the NOL approach each other rather rapidly and take roughly half the time to meet as compared with the time needed for such coalescence in the LOL. In the NOL, the soliton profiles can move freely and respond to the lattice periodicity when the separation between their initial locations are as twice as that needed for a similar free movement in the LOL. We observe that, in both cases, slow tuning of the optical lattices by varying k with respect to a time parameter τ drags the oscillatory solitons apart to take them to different locations. In our potential model the oscillatory solitons appear to propagate undistorted. But a fully numerical calculation indicates that during evolution they exhibit decay and revival.     

Analyses of Ne-diffraction data from transition-metal surfaces based on charge-density calculations

We evaluate the proportionality constant β for neon in the Esbjerg-Nørskov potential V_R(r) = βϱ(r) from experimental data on Ni(110), Ni(113), Cu(110) and Pd(110). Our calculations using overlapping atomic charge densities require that β be material and surface-dependent. Although Ne diffraction is more sensitive to details of corrugation shapes than He, we found it to be insensitive to normal relaxations of the topmost layers.     

Structure of dichlorine monoxide as studied by microwave spectroscopy. Determination of equilibrium structure by a modified mass dependence method

The microwave spectra of four isotopic species of dichlorine monoxide (OCl₂) have been observed, and the rotational constants have been obtained. The r_m structure for each isotopic species has been determined by Watson's method. The equilibrium structure has been estimated by taking proper averages of r_m structures to be $\text{r}{}_{\mathrm{e}}\text{(OCl) = 1.69587(7)}\text{A}\text{?}$ and ∠_eClOCl = 110.886(6)°. The general applicability and the merit of the present method for estimating the equilibrium structure are pointed out.