MRCI study of spectroscopic and molecular properties of X1Σg+ and A1Πu electronic states of the C2 radical

The potential energy curves (PECs) of X1Σ+g and A1Πu electronic states of the C2 radical have been studied using the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in conjunction with the aug-cc-pV6Z basis set for internuclear separations from 0.08 nm to 1.66 nm. With these PECs of the C2 radical,the spectroscopic parameters of three isotopologues ( 12C2 ,12C13C and 13C2 ) have been determined. Compared in detail with previous studies reported in the literature,excellent agreement has been found. The complete vibrational levels G(υ),inertial rotation constants B υ and centrifugal distortion constants D υ for the 12C2 ,12C13C and 13C2 isotopologues have been calculated for the first time for the X1Σ+g and A1Πu electronic states when the rotational quantum number J equals zero. The results are in excellent agreement with previous experimental data in the literature,which shows that the presented molecular constants in this paper are reliable and accurate.     

Intergranular Tunnelling and Field-Induced Percolation Fluctuation of Granular Composites （La1-zAgzMnO3）/（MnO2/Mn2O3）

We investigate the giant magnetoresistance of composites （La1-xAgzMnO3）1-υ（MnO2/Mn2O3）υ. The magnetoresistive property of the composites shows the characteristics of intergranular tunnelling. A conductivity leap has been observed around y = 0.7. The composite （La0.926Ag0.074MnO3）0.698（MnO2/Mn2O3）0.302 has been found to show the greatest magnetoresistance in the samples. Its room-temperature MR ratio reaches 24% under a field of 1.8T. These phenomena suggest a percolation transformation and a kind of field-induced fluctuation in percolation in the samples investigated.     

Laser spectroscopy of jet－cooled CuF in visible region

The laser-induced fluorescence excitation spectra of jet-cooled CuF have been recorded in the range of 19000－21470cm^{-1}, in which the CuF radicals were produced by the reaction of SF_6 with copper atoms from a dc discharge-sputtering source under supersonic jet conditions. Eight observed vibronic transition bands have been assigned as the transition from the ground state X(^1Σ^+) to B(^1Σ^+), C(^1Π) and an unreported upper state. The rotational structure of all observed bands has been analysed at the estimated rotational temperature 80K. We determined the newly observed band to be the (^1Π, v=1)－X(^1Σ^+v=0) transition according to the character of the rotational structure and the isotopic shift analysis. In addition, the lifetimes of the states involved in these bands were measured.     

Investigation of analytical harmonic frequency and potential energy function,vibrational levels for the X^2∑^＋ and A^2Л states of CN radical

This paper calculates the equilibrium structure and the potential energy functions of the ground state （X^2∑^＋） and the low lying excited electronic state （A^2Л） of CN radical are calculated by using CASSCF method. The potential energy curves are obtained by a least square fitting to the modified Murrell-Sorbie function. On the basis of physical theory of potential energy function, harmonic frequency （ωe） and other spectroscopic constants （ωeχe, βe and αe） are calculated by employing the Rydberg-Klei-Rees method. The theoretical calculation results are in excellent agreement with the experimental and other complicated theoretical calculation data. In addition, the eigenvalues of vibrational levels have been calculated by solving the radial one-dimensional SchrSdinger equation of nuclear motion using the algebraic method based on the analytical potential energy function.     

The effect of the rotational excitation of NO on the stereodynamics for the reaction C(~3P)+NO(X~2Π)→CN(X~2Σ~+)+O(~3P)

The stereodynamic properties of the reaction C(3P)+NO(X2Π)→CN(X2Σ+)+O(3P) in different rotational states of reactant NO are studied theoretically by using the quasiclassical trajectory method on 2A' and 2A' potential energy surfaces(PESs) at a collision energy of 0.06 eV.The vector properties in different rotational states on the two surfaces are discussed in detail.The results indicate that the rotational excitation of NO has considerable influence on the stereodynamic property of the reaction occurring on the two surfaces.At the same time,the calculated polarization-dependent differential cross sections(PDDCSs) in different initial rotational states manifest that products are strongly polarized at three scattering angles.     

Structural, Spectroscopic and Vibrational Properties for Low-Lying Electronic States of LiCl

A multireference configuration interaction(MRCI) study has been carried out on the LiCl molecule. The potential energy has been calculated over a wide range of internuclear separation for the 21 low-lying electronic states of the LiCl molecule dissociating into Li(2S,2P,3S)+Cl(2P). The(4)1Σ+,(3)1Π, 1-33Σ+, 1-33Π,1,3,1,3Σ,(5)1Σ+,(4)3Σ+,(4)1Π,(4)3Π excited states are studied for the first time in theory. Molecular spectroscopic constants(Re, De,ωe, ωeχe, Be and αe) have been derived for the 9 bound states(X1Σ+,(3)1Σ+,(2)3Σ+,1,3,1,3Σ,(4)1Π,(4)3Π) with a regular shape, and the spectroscopic constants of ground states X1Σ+are in good agreement with available experimental and theoretical values. The relative diferences between experimental values and our values for Re, De, ωe, ωeχe, Be andαe are 1.02%, 0.60%, 1.72%, 9.46%, 2.0%, and 0.75%, respectively. Moreover, vibrational levels of 9 bound states, which have not been investigated experimentally, are computed.     

Absorption spectra and isotope shifts of the(2, 0),(3, 1), and(8, 5) bands of the A~2Π_u-X~2Σ_g~+ system of ~(15)N_2~+ in near infrared

The high-resolution absorption spectra of the(2, 0),(3, 1), and(8, 5) bands of the A~2Π_u–X~2Σ_g~+system of~(15) N_2~+ have been recorded by using velocity modulation spectroscopy technique in the near infrared region. The rotational constants of the X~2Σ_g~+and A~2Π_u states of~(15) N_2~+ were derived from the spectroscopic data. The isotope shifts of these bands of the A~2Π_u–X~2Σ_g~+system of~(14) N_2~+ and~(15) N_2~+ were also analyzed and discussed.     

Configuration interaction studies on the spectroscopic properties of PbO including spin-orbit coupling

Lead oxide(Pb O), which plays the key roles in a range of research fields, has received a great deal of attention. Owing to the large density of electronic states and heavy atom Pb including in Pb O, the excited states of the molecule have not been well studied. In this work, high level multireference configuration interaction calculations on the low-lying states of Pb O have been carried out by utilizing the relativistic effective core potential. The effects of the core-valence correlation correction, the Davidson modification, and the spin–orbital coupling on the electronic structure of the Pb O molecule are estimated. The potential energy curves of 18 Λ-S states correlated to the lowest dissociation limit(Pb(~3P_g) + O(~3P_g)) are reported. The calculated spectroscopic parameters of the electronic states below 30000 cm~(-1), for instance, X~1Σ~+, 1~3Σ~+,and 1~3Σ~-, and their spin–orbit coupling interaction, are compared with the experimental results, and good agreements are derived. The dipole moments of the 18 Λ-S states are computed with the configuration interaction method, and the calculated dipole moments of X~1Σ~+and 1~3Σ~+are consistent with the previous experimental results. The transition dipole moments from 1~1Π, 2~1Π, and 2~Σ to X~1Σ~+and other singlet excited states are estimated. The radiative lifetime of several low-lying vibrational levels of 1~1Π, 2~1Π, and 2~1Σ~+ states are evaluated.     

Vibronic spectra of aluminium monochloride relevant to circumstellar molecule

The A^1Π→ X^1Σ^+ transition system of aluminium monochloride is determined by using ab initio quantum chemistry.Based on the multi-reference configuration interaction method in conjugate to the Davidson correction(MRCI + Q), the potential energy curves(PECs) of the three electronic states are obtained. Transition dipole moments(TDMs) and the vibrational energy levels are studied by employing the aug-cc-pwCV5Z-DK basis set with 4220-active space. The rovibrational constants are first determined from the analytic potential by solving the rovibrational Schr ¨odinger equation, and then the spectroscopic constants are determined by fitting the vibrational levels, and these values are well consistent with the experimental data. The effect of spin–orbit coupling(SOC) on the spectra and vibrational properties are evaluated.The results show that the SOC effect has almost no influence on the spectroscopic constants of AlCl molecules. For the A^1Π→ X^1Σ^+transition, the highly diagonalized Frank–Condon factor(FCF) is f(00)=0.9988. Additionally, Einstein coefficients and radiative lifetimes are studied, where the vibrational bands include ν'= 0–19→ν'=0–9. The ro-vibrational intensity is calculated at a temperature of 296 K, which can have certain astrophysical applications. At present, there is no report on the calculation of Al Cl ro-vibrational intensity, so we hope that our results will be useful in analyzing the interstellar Al Cl based on the absorption from A^1Π→ X^1Σ^+.     

Collisional broadening of some 2~1Δ_g←B~1Π_u lines in Na_2 molecules by optical-optical double resonance spectroscopy

Using the optical-optical double resonance (OODR) technique, we have studied the collisional broadening of some 2~1Δ_g←B~1Π_u lines in Na2 molecules. A single line Ar laser is used to pump the sodium dimers from thermally populated ground state X1∑ 9 level to the intermediate B~1Π_u state. Then, a single-mode diode laser is used to probe the doubly excited 21Δ_g state. The broadening rate coefficient is determined from the slope of the total linewidth versus Ne density curve. We obtain the average value kbr=(1.1±0.5)×10-8 cm3s-1. The collisional excitation transfer between rotational levels of the B~1Π_u state (i.e., B~1Π_u(2, 83/84)←B~1Π_u(2,82)) is also investigated. The rates can be determined from the relative intensities of the main peak and satellite lines, combined with a rate equation model. The rates of 1.25×10~6 and 1.07×10~6 s-1 are obtained, respectively.     

Controlling neutral fragmentation yields of methane by femtosecond laser pulses

We demonstrate the control of neutral fragmentation of methane（CH4） induced by a Ti：sapphire intense laser pulse（800 nm, 40 fs） by using a pump–probe spectroscopy. Enhancement of the fluorescence emission from the neutral radical CH（A2Δ → X2Π） induced by the intense laser field（~1014 W/cm2） is observed when the wavelength of the probe laser pulse is tuned to 400 nm. The phenomena are explained based on excitation enhancement of the super-excited state of the parent molecule resulting in an increase in neutral dissociation of the methane molecules.     

The structure and the analytical potential energy function of NH2 （X^2B1）

This paper reports that the equilibrium structure of NH2 has been optimized at the QCISD/6-311＋＋G （3df, 3pd） level. The ground-state NH2 has a bent （C2v, X^2B1） structure with an angle of 103.0582°. The geometrical structure is in good agreement with the other calculational and experimental results. The harmonic frequencies and the force constants have also been calculated. Based on the group theory and the principle of microscopic reversibility, the dissociation limits of NH2（C2v, X^2B1） have been derived. The potential energy surface of NH2（X^2B1） is reasonable. The contour lines are constructed, the structure and energy of NH2 reappear on the potential energy surface.     

Temportal Behaviour of Micro—discharge in Dielectric Barrier Discharges

A speical dielectric barrier discharge(DBD)device consisting of two water electrodes has been designed.The temporal behaviuour of the micro-discharge(filament)in the DBD in air at atmospheric pressure is measured by using an optical method.The nonsymmetrical characterstic of the filament has been discovered for the first time. We propose an equation regarding the discharge moment by considering the memory effect of the accumulated charge and the influence of the fluctuation.The results deduced from the equation give a good explanation of the experimental phenomenon,which show that the decay time constant of the accumulated charges is much larger than 100us.The relative intensity of fluctuation amplitude is in the range 2-4% under the present experimental conditions.     

Optical Oscillator Strengths of Hydrogen Bromide in the 4.5-20 eV Excitation Energy Region

The absolute optical oscillator strength density spectrum of HBr in the valence shell energy region of 4.5-20eV has been determined by a high-resolution fast electron energy loss spectrometer. The optical oscillator strengths for the broad a^3∏ A^1∏ dissociation peak and the discrete transitions orb ^3∏1 (v′=0) and C^1∏(v′=0,1,2) are     

Theoretical study on the band structure and optical properties of 4H-SiC

We have studied the band structure and optical properties of 4H-SiC by using a full potential linearized augmented plane waves (FPLAPW) method. The density of states (DOS) and band structure are presented. The imaginary part of the dielectric function has been obtained directly from the band structure calculation. With band gap correction, the real part of the dielectric function has been derived from the imaginary part by the Kramers－Kronig (KK) dispersion relationship. The values of reflectivity for normal incidence as a function of photon energy have also been calculated. We found the theoretical results are in good agreement with the experimental data.     

Bifurcations and observation of strange attractor in He-Ne lasers

We report the experimental observation of deterministic chaos in an He-Ne laserat 0.6328μm by varying the discharge current.Strange attractor of laser system in the recon-structed phase-space picture has been obtained.The mechanism of the phenomena was dis-cussed.     

String Cosmological Models in Five-Dimensional Spacetimes

We present some classes of solutions for dust matter coupled to the string cloud in five-dimensional Kaluza-Klein spacetimes. The solutions have one or two distinct singularities depending upon the sign of the constant of integration. Some of the classes of models exhibit inflation in the initial stage. The behaviour of associated parameters has been discussed in detail.     

Dynamical Casimir effect in superradiant light scattering by Bose–Einstein condensate in an optomechanical cavity

We investigate the effects of dynamical Casimir effect in superradiant light scattering by Bose-Einstein condensate in an optomechanical cavity. The system is studied using both classical and quantized mirror motions. The cavity frequency is harmonically modulated in time for both the cases. The main quantity of interest is the number of intracavity scattered photons. The system has been investigated under the weak and strong modulations. It has been observed that the amplitude of the scattered photons is more for the classical mirror motion than the quantized mirror motion. Also, initially, the amplitude of scattered photons is high for lower modulation amplitude than higher modulation amplitude. We also found that the behavior of the plots are similar under strong and weak modulations for the quantized mirror motion.     

Tailoring optical properties of TiO2 in silica glass for limiting applications

We present the linear and nonlinear optical studies on TiO2-SiO2 nanocomposites with varying compositions. Opti- cal band gap of the material is found to vary with the amount of SiO2 in the composite. The phenomenon of two-photon absorption （TPA） in TiO2/SiO2 nanocomposites has been studied using open aperture Z-scan technique. The nanocom- posites show better nonlinear optical properties than pure TiO2, which can be attributed to the surface states and weak dielectric confinement of TiO2 nanoparticles by SiO2 matrix. The nanocomposites are thermally treated and similar studies are performed. The anatase form of TiO2 in the nanocomposites shows superior properties relative to the amorphous and rutile counterpart. The involved mechanism is explained by rendering the dominant role played by the excitons in the TiO2 nanoparticles.     

Ab initio MRCI＋Q study on potential energy curves and spectroscopic parameters of low-lying electronic states of CS＋

Carbon monosulfide molecular ion （CS＋）, which plays an important role in various research fields, has long been attracting much interest. Because of the unstable and transient nature of CS＋, its electronic states have not been well investigated. In this paper, the electronic states of CS＋ are studied by employing the internally contracted multireference configuration interaction method, and taking into account relativistic effects （scalar plus spin–orbit coupling）. The spin–orbit coupling effects are considered via the state-interacting method with the full Breit–Pauli Hamiltonian. The potential energy curves of 18 Λ–S states correlated with the two lowest dissociation limits of CS＋ molecular ion are calculated, and those of 10 lowest Ω states generated from the 6 lowest Λ–S states are also worked out. The spectroscopic constants of the bound states are evaluated, and they are in good agreement with available experimental results and theoretical values. With the aid of analysis of Λ–S composition of Ω states at different bond lengths, the avoided crossing phenomena in the electronic states of CS＋ are illuminated. Finally, the single ionization spectra of CS （X1Σ＋） populating the CS＋（X2Σ1/2＋, A2Π3/2, A2Π1/2, and B2Σ1/2＋） states are simulated. The vertical ionization potentials for X2Σ1/2＋, A2Π3/2, A2Π1/2, and B2Σ1/2＋ states are calculated to be 11.257, 12.787, 12.827, and 15.860 eV, respectively, which are accurate compared with previous experimental results, within an error margin of 0.08 eV~0.2 eV.