Ab initio calculation of the He2 A 1Σ u +└X 1Σ g + absorption spectrum

The absorption spectrum of helium gas near 600 Å, assigned to the A ¹Σ _u ⁺└X ¹Σ _g ⁺ transition in He₂, is calculated at 77 K. The excited state potential is taken from a recent ab initio calculation. The theoretical spectrum shows well-defined bands, corresponding to different vibration levels of the A state, with diffuse rotational structure, in agreement with experiment. Fairly good quantitative agreement with Tanaka and Yoshino's measured spectrum is obtained, except for the somewhat too large separation between calculated vibrational bands, probably due to the theoretical potential for the A state rising too steeply at small inter-nuclear separation. Rotational constants derived from the calculated and experimental spectra are in good agreement. It is shown that they are significantly smaller than actual rotational constants of the upper state.     

The Hugoniot equation of state of the fluid He+D2 mixtures

The fluid variational theory and effective one-component model have been used to calculate the Hugoniot equation of state (EOS) of fluid He, D2, and He+D2 mixtures with different He:D2 compositions under high pressures and temperatures. An examination of the confidence of above computation is performed by comparing experiment and calculation, in which the similar calculation procedure used for He+D2 is adopted, of He and D2 each, since no experimental data are available to conduct this kind of comparison. Good agreement in both comparisons is found. This fact may be looked as if an indirect positive verification of calculation procedure used here at least in the pressure and temperature domain covered by the experimental data of He and D2 used for comparison, numerically nearly up to 35 GPa and 105K.     

Time spectroscopy in theA 1 ∑ u + state of Li2. Perturbations by thea 3Π u state

We have employed time-resolved LIF spectroscopy in order to investigate perturbations in theA ¹ ∑ _u ⁺ state of the three isotopic Li₂ molecules. After a systematic check of more than 2000 individual rotation-vibration levels, 46 levels were found whose anomalous lifetimes can be interpreted by perturbations with thea ³ Π _u state. As almost all perturbed levels possess shortened lifetimes the predissociating nature of thea ³ Π _u state, caused by interaction with thex ³ ∑ _u ⁺ continuum, is revealed. On the basis of the Kovács-Budo theory of accidental predissociation we have fitted the molecular constants of thea ³ Π _u state, thex ³ ∑ _u ⁺ potential curve and the electronic parts of the perturbation matrix elements do that the observed lifetimes of all levels in the 78 investigatedA ¹ ∑ _u ⁺ ?a³ Π _u term-crossing regions can be understood.     

A quasiclassical study of collisions of He with HD(B 1Σ+ u )

A quasiclassical trajectory study has been carried out for collisions of ⁴He with electronically excited H₂(B ¹Σ⁺ _u ) and its isotopomer HD. By using analytical fits for the ab initio potential energy surfaces of the ground and the excited state we have obtained vibrational and electronic quenching cross sections for several initial conditions. We draw the following conclusions. Vibrational excitation strongly promotes electronic quenching whereas translational energy is less effective. Rotational excitation decreases the rate of quenching. In a remarkable contrast to the ground electronic state, vibrational energy transfer on the excited potential energy surface is an efficient and fast process. Collisions at high energies results in T → R energy transfer. The above conclusions are valid for both H₂ and HD.     

A tentative multiphoton ionization of CS2 molecule: Spectroscopy of Ã2πu state of CS 2 + ion

The spectroscopic study of excited molecular cationCS ₂ ⁺ (òπ_u ) by a different method is presented. In this technique the decay of excited states is monitored by measuring the photons emitted. The peaks in the photon spectrum would correspond to the energy levels of the ion. The vibrational-vibrational, vibrational-electronic interactions have been observed. Symmetry forbidden excitation of one quantum of bending vibration is observed which gives unperturbed value for the bending vibration. The Renner-Teller splitting for the δ_g and Σ _g ^- components of the bending mode (v ₂ ^′ = 1) in the upper excited òπ_u state has been observed. A tentative vibrational analysis of the Ã→ X system has been made.     

Potential energy functions for the ground state X3Σ- and excited state 1Σ+ of UO

Based on group theory and atomic and molecular reactive statics (AMRS), the ground state X³Σ^? and excited state ¹Σ⁺ of UO and their reasonable dissociation limits are derived successfully. Using the MP2 method with the relativistic e? ective core potential and valence electron basis set (5s4p3d4f)/[3s3p2d2f] for the U atom and basis set 6-311G* for the O atom, the present work has calculated the potential energy curves for the ground state Χ³Σ^? and excited state ¹Σ⁺ of UO. The equilibrium distance and dissociation energy are 0.1833 nm and 6.9241 eV for the Χ³Σ^? state, and 0.1825 nm and 8.8756eV for the ¹Σ⁺ state. Spectroscopic data are derived for the first time.     

Calculation of molecular constants for the X 1Σ g + , A 1Σ u + , B 1Πu, and a 3Σ u + electronic states of 39K2

The molecular constants are calculated for the X ¹Σ _g ⁺ , A ¹Σ _u ⁺ , B ¹Π_u, and a ³Σ _u ⁺ and electronic states of a potassium dimer. The wave functions and vibrational energies necessary for calculating the molecular constants are determined by solving the radial wave equation with the use of potential energy curves constructed by the semiempirical method. The vibrational terms, the rotational constants, and the centrifugal distortion constants calculated from the potential curves are compared with those determined from the experimental data.     

Contribution of the lowest 1+ intermediate state to the 2νββ-decay amplitude

The half-life with respect to two-neutrino double-beta (2νββ) decay to the final ground state is calculated under the assumption of single-state dominance. To the best of our knowledge, the energy denominators of perturbation theory are considered for the first time without invoking any approximation. The results obtained for the experimentally interesting A=100, 110, 114, 116, and 128 nuclear systems are presented.     

The high-resolution spectrum of the ν1 + ν2 band of NO2: A spin-induced perturbation in the ground state

The spectrum of the ν₁ + ν₂ band of NO₂ has been studied with a resolution of 0.025 cm⁻¹. Spin-rotation constants and rotational constants are reported. An interesting perturbation has been found in the ground state of the molecule which occurs when the K_a = 0 and K_a = 2 levels become accidentally nearly degenerate around N = 42. An explanation of this interaction is presented.     

The rotational spectrum of the SH radical in its XΣ state

All the available data on the rotational energy levels of the SH⁺ (sulfoniumylidene) radical in the v = 0 and 1 levels of the X³Σ⁻ ground state have been subjected to a single, weighted least-squares fit to determine an improved set of molecular parameters for this molecule. The results have been used to calculate the rotational spectrum of the SH⁺ radical in the v = 0 and 1 levels up to the N = 4-3 transition.     

Polarization spectroscopy of Na2 A1Σu+-b3Πu ← X1Σg+ intercombination bands

The A¹Σ_u⁺ ∼ b³Π_u perturbation of Na₂ in several high vibrational levels has been studied by polarization spectroscopy. Deperturbed molecular constants are given for the mutually interacting v_A = 26 ∼ v_b = 28 and v_A = 34 ∼ v_b = 34 vibrational levels.     

Absolute population of the A 3 Σ u + metastable state of a nitrogen molecule in a glow discharge plasma

The absolute populations of seven vibrational levels of the B ³Π_g state of a nitrogen molecule in a negative glow are determined at a pressure of 0.01–5.00 Torr and a current of 100–400 mA from the absolute intensity of the lines of the nitrogen first positive system. The population of the A ³Σ _u ⁺ metastable state at different discharge parameters is found using the balance equation for this state.     

Determination of the population of the A 3Σu electronic state of nitrogen molecules in a glow-discharge plasma

Results on determining the population of the A ³Σ_u electronic state of N₂ molecules in a gas discharge using a relatively simple spectroscopic technique are reported. The technique proposed can be used not only in pure N₂, but also in nitrogen-containing gas mixtures. The populations of the metastable and nonequilibrium B ³Π_g states of nitrogen molecules are determined. It is shown that the electron-impact excitation is a dominant mechanism for populating the B ³Π_g state.     

Radiative lifetime measurements of vibrational levels of Cl2 + A 2Π u

The radiative lifetimes of several vibrational levels of Cl₂ ⁺ A ²Π _u are measured by a novel technique. A uniform electric field extracts the ions from the observation region of a spectrometer, and the decrease of fluorescence signal as a function of the electric field strength is measured to obtain the radiative lifetime. Measurements are made on 20 different vibronic bands of the Cl₂ ⁺ A ²Π _u -X ²Π _g system, and the results are compared with other methods. An attempt is made to correlate the results with the highly perturbed spectroscopic nature of the A ²Π _u electronic state.     

Potential cluster approach to the description of the 7Li + γ ai p6He reactions

Angular distributions for the ⁶He(p, γ_{0 + 1})⁷Li process at the energy E _γ = 40 MeV are calculated within the potential cluster approach. It is shown that the observed cross section is well reproduced when E1 and E2 transitions are taken into account; in this case, unlike the case in the RGM calculations, the dominating mechanism is direct capture to the ground state of the ⁷Li nucleus. Total cross sections for direct photodisintegration ⁷Li (γ, p₀)⁶He in the energy interval E _γ = 22–30 MeV are calculated.