Variational calculations of vibrational energy levels for XY4 molecules 1. Stretching states

A variational method for calculating excited stretching states of symmetric tetrahedral pentaatomic molecules is presented based on the use of Radau coordinates and Morse oscillator-like basis functions. Symmetry is used both to reduce the size of the secular matrix to be diag-onalized and to calculate the potential energy matrix elements over a reduced grid of quadrature points. Test results are presented for methane, silane and germane. For CH₄, stretch-bend coupling is found to be significant, whereas it is less important for the more strongly local mode SiH₄ and GeH₄ molecules. Converged results are obtained for stretching states significantly higher than considered in previous calculations. These states will be used to represent stretching motions in a fully coupled stretch-bend calculation.     

Simulation study of solvent shifts of vibrational overtone spectra

Buckingham's theory of the solvent shift of vibrational spectral frequencies predicts that the shift of the v = 0 → n overtone transition is n times the shift of the fundamental v = 0 → 1. We test this prediction by molecular dynamics simulations using existing intermolecular potential models for liquid N₂ and dilute N₂ in liquid Ar, at standard state conditions. We extend Buckingham's theory by including additional intramolecular potential and perturbation terms which lead to solvent-induced anharmonicity, i.e. O(n ²) terms in the solvent shift. The simulations show that Buckingham's prediction is not accurate for N₂ at standard liquid state conditions. We find that at these conditions there is a significant positive O(n ²) contribution to the solvent shifts and that for n ～ 20 the shifts change sign from red to blue. Simulation results and indirect evidence from shock wave experiments with liquid N₂ show that Buckingham's prediction is more accurate for high-pressure high-temperature conditions, where the shifts are blue and only slightly nonlinear in n.     

Collision induced dissociation of laser irradiated silicon tetrafluoride

The time development of visible fluorescence from CO₂-laser-irradiated SiF₄ at various pressures is compared to the predictions of a simple model. This comparison leads to the conclusion that dissociation is a result of binary collisions between molecules that are vibrationally excited but translationally cool.     

Collisional broadening and shifting of saturated absorption resonances in silicon tetrafluoride

The broadening and shifting of 12 saturated absorption resonances of the SiF₄ gas induced by molecular collisions have been measured in the lasing region of a low-frequency CO₂ laser at the P(30) line of the 9.4-μm band. Values of the collisional broadening are identical accurate to the measurement uncertainty. The collisional shift does not exceed 10% of the collisional broadening. This means that collisions with changes in the internal energy of molecules prevail over dephasing collisions.     

Rotational and vibrational states in 115Te

High-spin states of the ¹¹⁵Te were studied by in-beam spectroscopy with the ⁸⁹Y (²⁹Si, p2n) fusion-evaporation reaction at a beam energy of 108 MeV. γ?γ coincidence and γ?γ angular correlation analyses were employed for determining the level scheme of ¹¹⁵Te. We have identified two vibrational-like bands built on the νh_11/2 and νg_7/2 quasiparticle states and the noncollective oblate states from the full alignment of quasiparticle configurations. In addition, a regular ΔI = 2 sequence with positive-parity was found for the first time in odd-A Te nuclei. This sequence is interpreted as a deformed structure resulting from three-quasiparticle alignment having the [π(g_7/2, h _11/2) ? ν(h _11/2)] configuration. Calculations of total Routhian surfaces and cranked shell model were performed and were used for assigning quasiparticle configurations to the states in ¹¹⁵Te.     

Correlation of electronic states of the positive ions of xenon tetrafluoride,xenon oxide tetrafluoride,and iodine pentafluoride

A correlation of electronic states of XeF₄⁺, XeOF₄⁺ and IF₅⁺ is presented. The results are interpreted in terms of the molecular orbitals of the neutral molecules via Koopmans' Theorem. The results strongly suggest that the first band in the ultraviolet photoelectron spectrum of XeOF₄ contains only two electronic states. Consequently, the Xe-O σ bond in XeOF₄ is at least 1.5 eV more stable than the corresponding xenon lone pair in XeF₄. The interpretation of oxygen lone pair electron energies is complicated by ionic and covalent effects, both tending to stabilize these electrons.     

Calculations of molecular ir spectra in the overtone and combination frequency regions

Frequencies and intensities of fundamental, overtone, and combination absorption bands have been calculated in an anharmonic approximation for substituted benzene and ethene, aldehydes, ketones, and alcohols in the range 400–4000 cm^–1. The calculated values agree well with the experimental data. It is shown that such a calculation allows one to study and predict dependences of the frequencies and intensities of the overtone and combination bands on the substance structure.     

The analysis of combination and overtone states of BF3 from 1650 to 4600 cm

High-resolution (0.0015-0.0035 cm⁻¹) infrared spectra of isotopically enriched ¹¹BF₃ have been examined in detail. The analysis of the combination and overtone states within the region of study, from 1650 to 4600 cm⁻¹, led to the assignment of over 25,000 transitions. The major perturbations were due to the Fermi resonances between states possessing one quantum of v₃ and three quanta of v₄. With corrections through the quadratic rotational terms, the equilibrium B_e and C_e values have been determined; 0.3462679(7) cm⁻¹ and 0.1731151(6) cm⁻¹, respectively. An improved set of equilibrium rotational constants for ¹⁰BF₃, consistent with this analysis of ¹¹BF₃ are also given. The averaged equilibrium values for both isotopomers lead to a B-F bond distance of r_e = 130.704 ± 0.005 pm. All of the quadratic anharmonic constants, with the exception of x³³ were independently determined from experiment. For the first time for BF₃, a normal force field analysis was performed that utilized the experimentally determined, fundamental harmonic vibrational frequencies.     

Structure-dependent vibrational lifetimes of hydrogen in silicon

The lifetimes of the Si-H vibrational stretch modes of the H(*)(2) ( 2062 cm(-1)) and HV.VH((110)) ( 2072.5 cm(-1)) defects in crystalline Si are measured directly by transient bleaching spectroscopy from 10 K to room temperature. The interstitial-type defect H(*)(2) has a lifetime of 4.2 ps at 10 K, whereas the lifetime of the vacancy-type complex HV.VH((110)) is 2 orders of magnitude longer, 295 ps. The temperature dependence of the lifetime of H(*)(2) is governed by TA phonons, while HV.VH((110)) is governed by LA phonons. This behavior is attributed to the distinctly different local structure of these defects and the accompanying local vibrational modes.     

Muonium states in silicon carbide

Implanted muons in samples of silicon carbide have been observed to form paramagnetic muonium centers (μ ⁺ e⁻). Muonium precession signals in low applied magnetic fields have been observed at 22 K in a granular sample of cubic β-SiC, however it was not possible to determine the hyperfine frequency. In a single crystal sample of hexagonal 6H-SiC, three apparently isotropic muonium states were observed at 20 K and two at 300 K, all with hyperfine frequencies intermediate between those of the isotropic muonium centers in diamond and silicon. No evidence was seen of an anisotropic muonium state analogous to the Mu^* state in diamond and silicon.     

Donor states in tellurium-doped silicon

Hall effect and conductivity measurements are performed on Te-doped silicon in the temperature range 30KT800K. A Hall equipment suited for high temperatures up to 800 K has been constructed. The temperature dependence of the free electron concentration is analyzed for Te-doped silicon including one double-donor and several monovalent donor species. A deep level with an electrical activation energy of 200 meV is determined from the saturation of the free electron concentration at temperatures above 400 K. This level represents the first ionization stage of the Te double-donor. The second ionization stage is estimated to have an activation energy of 440 meV. The maximum electrically active Te concentration obtained is 5×10¹⁶cm^–3. Three different shallow donor states are resolved in the low-temperature range. The concentrations of these shallow donors are partially sensitive to a subsequent heat-treatment.     

Low-lying vibrational states of145,147,149Nd

The fragmented neutron states in^145,147,149Nd detected through¹⁴⁴Nd(d, p) and^148,150Nd(d, t) reactions can be accounted for in terms of quasiparticles coupled with anharmonic vibrator model. The wave functions, obtained from diagonalisation of the Hamiltonian matrices are utilised to calculate B(E2), B(M1) and branching ratios in^145,147Nd. The calculated results are discussed in the light of the recent experimental findings.     

WF6分子伸缩振动能谱的非线性模型计算

利用一个四参数非线性模型对处于电子基态下的XY6型分子的X-Y键的伸缩振动进行了描述,并将其应用于计算WF6分子中W-F键的伸缩振动能级.计算中引入的模型Hamilton算符所包含的描述WF键非谐振动的参数λ和描述WF键之间的偶极-偶极相互作用参数ε1,ε2由实验值得出,波函数 |ψn〉按形式为|n,α〉=|n1〉|n22〉|n3〉|n4〉|n5〉|n6〉的基函数集展开,从而把复杂的Hamilton方程转化为简单的矩阵代数方程.结果显示该非线性模型能够较好地描述了WF6分子的振动(计算误差在0.6 cm-1之内),同时合理地预测了一些至今还未观测到的能级值.