The ν2 Raman band of CD4

The rather weak ν₂ Raman band of CD₄ has been recorded with a resolution of about 0·45 cm^-1. The data have been analysed in two ways: (i) treating ν₂ as an isolated band, and (ii) analysing the ν₂ and ν₄ bands together by a simultaneous diagonalization of the v ₂=1 and v ₄=1 states coupled by the Bζ_2,4 Coriolis interaction term. Although the former treatment is satisfactory for low J values, the explicit inclusion of the Coriolis coupling is necessary to reproduce the observed spectrum for all J values.     

High-resolution infrared spectrum of acetylene in the region of the bending fundamental v 5

The infrared spectrum of C₂H₂ in the region of the bending fundamental v ₅ has been studied at a resolution of about 0·015 cm^-1. The molecular constants G ₀(v ₅=1) = 730·3341 (1) cm^-1 and B ₀ = 1·176641 (2) cm^-1 have been derived. In addition to the fundamental, all the hot bands starting from the levels v ₄ and v ₅ have been investigated. The vibrational, vibration-rotation coupling and centrifugal constants for the excited vibrational states v ₅ = 2 and v ₄ = v ₅ = 1 have been derived using the vibration-rotation energy matrix.     

The rotational spectrum of 13C2HD in the ground and excited bending states

The pure rotational spectrum of ¹³C₂HD was recorded in the range 100–700 GHz. Lines belonging to the ground vibrational state were observed from J^″ = 1 to J^″ = 11. Several absorption lines were also detected in the bending states v₄ = 1 (Π), v₅ = 1 (Π), v₄ = 2 (Σ⁺ and Δ), v₅ = 2 (Σ⁺ and Δ), v₄ = v₅ = 1 (Σ^?, Σ⁺ and Δ), v₄ = 3 (Π and Φ) and v₅ = 3 (Π and Φ). The transition frequencies measured in this work were fitted together with all the infrared lines available in the literature. The global fit allowed a very accurate determination of the vibrational, rotational and ?-type interaction parameters for the bending states of this molecule.     

The millimeter-wave spectra of germyl fluoride in excited vibrational states

Millimeter-wave spectra of GeH₃F in the v₃ = 1, v₆ = 1, v₂ = 1, and v₅ = 1 excited states have been recorded. Strong Coriolis resonance between the v₂ = 1 and v₅ = 1 states results in a highly perturbed spectrum which shows no obvious resemblance to the normal symmetric top excited state pattern. A similar, but not so strong coupling, exists between the v₃ = 1 and v₆ = 1 states. These spectra are analyzed by setting up the Coriolis coupled Hamiltonian matrices for these states. It has been shown that the apparently anomalous distortion constants of these states are due to the Coriolis coupling and the distortion parameters obtained with the model presented are, as expected, close to the ground state values.     

Torsion—rotation interactions in monodeuterated acetaldehyde

This paper presents an analysis of previously observed rotational transitions up to J = 17 of the sym and asym rotamers of monodeuterated acetaldehyde using a three-level Hamiltonian incorporating connections between rotational states of the v_sym = 0, v_asym = 0⁺ and v_asym = 0 ^? torsional energy level manifolds. Rotational transitions observed to be significantly perturbed in earlier studies, where the spectrum was fitted using a single-level Hamiltonian for the v_sym = 0 torsional state and a separate two-level Hamiltonian for the non-rigid asym states, are now fitted satisfactorily. It is confirmed that the perturbations detected in the earlier studies and tentatively attributed there to torsion-rotation interactions between the energetically distinct sym and asym manifolds do indeed arise as a consequence of such interactions. Rotational and quartic centrifugal distortion constants are given for each torsional state, together with torsion-rotation coupling constants primarily responsible for the perturbations noted in the earlier studies. Tunnelling between the energetically distinct sym and asym potential wells of the torsional potential energy function is also discussed.     

Vibration-inversion-rotation spectra of ammonia: Centrifugal distortion, Coriolis interactions, and force field in NH3, NH3, ND3, and NT3

An effective inversion-rotation Hamiltonian has been developed for NH₃ which avoids the necessity of having to include high powers of the inversion motion coordinate in the Taylor expansions of the potential energy and the inverse moment of inertia tensor. This nonrigid bender Hamiltonian describes the centrifugal distortion and the Coriolis interactions in the ground and excited inversion states. It also describes the inversion doublings in the ground and excited vibration-inversion states of ammonia. A least-squares procedure that includes the numerical integration of the Schrödinger wave equation has been used to determine the harmonic force field and the double-minimum inversion potential function for (¹⁴NH₃, ¹⁵NH₃) and for (¹⁴ND₃ and ¹⁴NT₃).The anomalous rotational dependence of the inversion doublings in the (±l) components of the v₄ = 1 state of ¹⁴NH₃ has been explained by the Coriolis interactions between v₂=1, v₄ = 1, v₂ = 2, v₂ = 1, v₄ = 1, and v₂ = 3 vibration-inversion states.     

Radiation defects in Si of high purity

Abstract

Radiation defects created by γ-irradiation of Co⁶⁰ and fast neutrons in high purity p-Si (p = 5×10³ to 4 × 10⁴ Ω.cm) and n-Si (p = 4 × 10² to 5 × 10³ Ω.cm) are investigated by measurements of Hall effect, resistivity and minority carrier lifetime. The oxygen concentration in the crystals is in the range of 5 × 10¹⁴ to 5 × 10¹⁵ cm^?3.

It is shown that stable γ-defects at 300 °K are divacancies and complexes of vacancies with donor or acceptor impurities. Divacancies introduced by γ-irradiation are the secondary defects. They become predominant after ‘exhaustion’ of the dopant. When divacancies become the predominant defects the Fermi level occupies its boundary position E_v +0.39 eV in the gap. At low doses (Φ<10¹⁶ photons/cm²) vacancy-impurity complexes and at heavy doses (Φ>10¹⁷ photons/cm²) divacancies play the main role in the recombination process.

In neutron irradiation disordered regions are introduced and the level at E_v +0.35 eV is observed. The Fermi level in both n- and p-Si shifts to the middle of the gap. At the annealing of disordered regions in the interval 200 to 250 °C the level at E_v +0.27 eV appears and Fermi level occupies its boundary position at E_v +0.39 eV. This indicates that divacancies become the predominant defects which can be formed as secondary defects at the destruction of the disordered regions.     

Microwave spectra and centrifugal distortion constants of oxetane

The microwave spectra of oxetane (trimethylene oxide) and its three symmetrically deuterated isotopic species have been observed on a Hewlett-Packard microwave spectrometer from 26.5 to 40 GHz. For the parent species, the β-d₂ and the αα′-d₄ species, about 300 lines have been assigned for each molecule, and for the d₆ species more than 600 lines have been assigned. The assignments range from v = 0 to v = 5 in the puckering vibration; although they are mostly Q transitions, either 3 or 4 R transitions have been observed for each vibrational state.The spectra have been interpreted using an effective rotational hamiltonian for each vibrational state, including five quartic distortion constants according to Watson's formulation, and a variable number of sextic distortion constants; in general, the lines are fitted to about ± 10 kHz. The distortion constants show an anomalous zig-zag dependence on the puckering vibrational quantum number, similar to that first observed for the rotational constants by Gwinn and coworkers. This is interpreted according to a simple modification of the standard theory of centrifugal distortion, involving the double minimum potential function in the puckering coordinate.     

Rovibrational states of H+ 3. Part 2: The energy region between 9000 cm−1 and 13000 cm−1 including empirical corrections for the non-adiabatic effects

The first part of this series focused on the calculation of the rovibrational states of H⁺ ₃ in the energy region below 9000 cm^?1, where most of the experimentally determined and assigned term values are located. The theoretically justified empirical correction for the non-adiabatic coupling corrections, which was obtained and tested in that study is extended and applied here in the calculation of the rovibrational states of H⁺ ₃ to term values up to 13000 cm^?1, which is above the barrier to linearity. In particular, predictions are made for the 5v ₂ bands, which are the subject of current experimental investigations, hopefully aiding with our results in the assignment of the spectral lines observed.     

Three-dimensional relativistic-covariant poisson brackets

Using the algebraic properties of Poisson brackets, we extend the three-dimensional brackets (for a single free particle) to conform to the demands of special relativity. This yields, in an essentially unique way, the manifestly covariant extension [x ,p _v]=+p p _v/m ² c ². Position and time then become fully dynamical variables expressible in terms of the canonical conjugateq _i andp _i and the time parameter asx _i =q _i +p _i(q ·p)/m ²c² andt = +E(q ·p)/m ²c⁴. In the quantized version, the length associated with a particle of massm is shown to be an integral multiple of the Compton wavelength _C =/mc.     

Two-photon resonant four-wave mixing in atomic sodium vapour

Using the 4d- and 5s-states of sodium, two different types of two-photon resonance enhanced four-wave mixing have been observed. In the first type 2v _L =v _IR +v _pIR radiation near 2.34 μm and UV radiation near 320 nm has been detected. In the second typev _P −v _S =v _L +v _IR the UV radiation produced in the first parametric process acted as a pump for stimulated electronic Raman scattering via the 4p-state of sodium. Resonantly enhanced by the two-photon transition 3s–4s, radiation near 1.18 μm was produced in this scheme. The realisation of a tunable coherent IR source based on these four-wave mixing processes is discussed.     

Dependence of transport characteristics of molecules on the rotational quantum number

We derive a simple analytic formula that describes the relative difference of transport collision rates, Δv/v, for collisions of molecules and atoms in the rovibrational excitation of the former by light, as a function of the rotational quantum numbers of the combining (i.e., affected by radiation) levels of the molecules. (The relative difference of transport collision rates can be measured in light-induced drift, or LID, experiments and is proportional to the LID effect.) The formula is valid in the energy sudden approximation and is based on the well-known factorization formula for cross sections of RT-transitions in linear molecules that collide with atoms. We show that in this approximation the factor Δv/v is the sum of two independent terms, the vibrational term (Δv/v)_vib and the rotational term (Δv/v)_rot. Each term can be measured individually in LID experiments. Zh. éksp. Teor. Fiz. 113, 1649–1660 (May 1998)     

The microwave spectrum of cyanoacetylene in ground and excited vibrational states

Microwave transitions are reported for ten isotopic species of cyanoacetylene in the ground, v ₄, v ₆, v ₆ and v ₇ vibrational states in the region 26·5-40·0 GHz. In addition millimetre-wave transitions of HCCCN and DCCCN in the ground v ₅, v ₆ and v ₇ vibrational states in the region 54·5-211·8 GHz have been measured. The combined data have been analysed to yield B_v, D_v, γ_rs, γ_ltlt′ and q_t vibration-rotation parameters, for HCCCN and DCCCN.

In addition millimetre-wave measurements pertaining to the v ₆ + v ₇ and v ₅ + v ₇ vibrational states have been analysed to give values for r_tt′J and approximate values of g_tt′ and r_tt′ (t = 5, 6; t′ = 7).

Rotational constants B_v in the first excited state of the fundamental vibrations v ₄, v ₅, v ₆ and v ₇ are combined with infra-red values for v ₁, v ₂ and v ₃ to give B_e for both HCCCN and DCCCN.     

l-type doubling of the kl = −1 levels in the microwave spectrum of the C4v molecule BrF5

Measurements are reported for the J 3 → 4, 4 → 5, and 5 → 6 transitions of BrF₅ in the excited vibrational states v₅(B₁) = 1 and v₉(E) = 1. These two states are nearly degenerate and an unusually strong Coriolis interaction perturbs both excited state spectra. New expressions are obtained for the E-species absorption frequencies which are valid in a strong Coriolis resonance situation. The analysis of the E-state spectrum has provided the first experimental observation of the doubling of the kl = −1 levels predicted for molecules with C_4v symmetry.     

The effect of surface temperature on H2/D2(v = 0, j = 0)–Ni(100) scattering processes

We carry out both four-dimensional (4D×2D) and six-dimensional (6D) quantum dynamics on a parametrically time- and temperature-dependent effective Hamiltonian for H₂/D₂(v = 0,j = 0)–Ni(100) collision process. Such an effective potential was derived within a theoretical framework of mean-field approximation by considering weakly correlated interaction between molecular degrees of freedom, phonon modes and electron– hole pair (elhp) coupling through a Hartree-product-type wave function, where the initial state distribution of the surface modes and elhp coupling were introduced through Bose– Einstein and Fermi– Dirac probability factor, respectively. The temperature-dependent dissociation and state-to-state transition probabilities for H₂/D₂(v = 0,j = 0)–Ni(100) system are depicted as a function of initial kinetic energ of the incoming diatom. Though such effect appears negligibly small for H₂(v = 0,j = 0)–Ni(100) system, it is prominent in the case of D₂(v = 0,j = 0)–Ni(100) collision. It appears that the change of dissociation and transition probabilities of D₂ with the increase of surface temperature is exclusively dictated by the phonon modes directed along Z-axis, but the effect of elhp coupling particularly for transition probabilities is insignificant.     

High-resolution FTIR spectra of CH2 = CClF in the 930-1050 cm−1 region

The gas-phase infrared spectra of natural CH₂ = CClF have been measured in the v ₆ and 2v ₁₂ band regions (930–1050 cm^?1) by high-resolution Fourier transform spectroscopy at room temperature. 1-Chloro-1-fluoroethylene is a planar asymmetric rotor (κ = ?0.54) belonging to the symmetry point group C_s and the vibrations investigated of symmetry species A′ give rise to a/b-hybrid bands with contributions of comparable intensity from both the components.

The rovibrational analysis of the fine structure led to the identification of 1894 (J ? 73, K_a ? 20) and 718 (J ? 53, K_a ? 8) transitions for the v ₆ and 2v ₁₂ bands of the ³⁵Cl isotopic species, respectively. Using the Watson's A-reduction Hamiltonian in the I^r representation a set of accurate spectroscopic parameters for both the excited states u ₆ = 1 and u12 = 2 of ³⁵Cl has been obtained for the first time. Transitions of ³⁷Cl isotopomer could also be assigned in the Q branch region of the 2v ₁₂ overtone; the determined band origin shift of 0.782 cm^?1 towards the lower wavenumbers led to describing the v ₁₂ fundamental as a vibration mainly involving the CFCl bending motion.     

Competition mechanism between singlet and triplet superconductivity in the tight-binding model with anisotropic attractive potential

Based upon the tight-binding formalism a model of a high-T_c superconductor with isotropic and anisotropic attractive interactions is considered analytically. Symmetry facets of the group C_4v are included within a method of successive transformations of the reciprocal space. Complete sets of basis functions of C_4v irreducible representations are given. Plausible spin-singlet and spin-triplet superconducting states are classified with regard to the chosen basis functions. It is displayed that pairing interaction coefficients and the dispersion relation, which can be characterized by the parameter η= 2t₁/t₀, have a diverse and mutually competing influence on the value of the transition temperature. It is also shown that in the case of a nearly half-filled conduction band and an anisotropic pairing interaction the spin-singlet d-wave symmetry superconducting state is realized for small values of the parameter η, whereas in the opposite limit, for sufficiently large values, the spin-triplet p-wave symmetry superconducting state has to be formed. This result cannot be obtained within the Van Hove scenario or BCS-type approaches, where the p-wave symmetry superconducting state absolutely dominates. The specific heat jump and the isotope shift as functions of the parameter η are assessed and discussed for the d-wave symmetry singlet and the p-wave symmetry triplet states.     

Simultaneous analysis of the ν2 and ν4 bands of methane

Vibration-rotation spectra of the ν₂ and ν₄ bands of CH₄ have been analysed by a simultaneous diagonalization of the hamiltonian matrices for the v ₂=1 and v ₄=1 states coupled by the Bξ_2,4 Coriolis interaction term. The effective hamiltonians used extend to sextic centrifugal distortion terms. The results are a significant improvement on any previous analysis; 438 assigned transitions up to J′=16 have been fitted with an overall standard deviation of 0·016 cm^-1. The method used is compared with an alternative theoretical approach given by Berger.     

N.M.R. investigation of critical orientational order fluctuations below the nematic-isotropic transition in liquid crystals

The high-resolution infra-red spectrum of SiH₄ in the region 2101 cm^-1 to 2265 cm^-1 has been analysed. Most of the lines observed have been assigned to transitions of the v ₃ and v ₁ bands of the abundant isotopic species ²⁸SiH₄. The v ₁ band is formally forbidden in the infra-red, but a vibration-rotation interaction between v ₁ and v ₃ lends intensity to the v ₁ transitions. The spectrum has been fitted by diagonalizing the v ₃ = 1 and v ₁ = 1 hamiltonians coupled by the vibration-rotation interaction term. 500 transitions have been fitted with an overall standard deviation of 0·007 cm^-1, using only 15 adjustable parameters (ten in the v ₃ = 1 hamiltonian, four in the v ₁ = 1 hamiltonian, and one interaction coefficient). The calculated intensities are also in good agreement with experiment. Transitions of the other isotopic species ²⁹SiH₄ and ³⁰SiH₄ have also been observed, but these spectra have not been analysed in detail.