State X1Σ Research Articles

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.

Configuration interaction study on the low-lying electronic states of indium antimonide

Large scale ab initio based multireference singles and doubles configuration interaction calculations have been performed to investigate the spectroscopic properties of the low-lying electronic states of indium antimonide (InSb). Relativistic effective core potentials and spin–orbit operators are used for this purpose. Potential energy curves of Λ-S states which correlate with lowest three dissociation limits are also computed. The ground state X3Σ−of InSb is dominated by the …σ2π2 configuration with re=3.02Å and ωe=139cm−1. The ground-state dissociation energy of InSb has been calculated to be 1.22eV which is somewhat smaller than the re-estimated experimental value of 1.45eV. Effects of the spin–orbit coupling on the spectroscopic parameters and potential energy curves of those states which correlate with the lowest two dissociation limits are studied. The spin–orbit interaction splits the ground state into two components which are 429cm−1 apart. The 0+ component of the ground state lies below the other component with Ω=1. Transition moments of some dipole allowed transitions are computed from configuration interaction (CI) wave functions. Radiative lifetimes of six excited states of InSb are estimated. The A3Π state is short-lived with a lifetime of about 530ns. The A3Π0+ component which does not predissociate undergoes symmetry allowed transitions with ΔΩ=0,1, and the total lifetimes of this state at three vibrational levels v′=0, 1 and 2 lie in the range 2.25–2.5μs.

Electronic Structure Study of the N2O Isomers Using Post-Hartree−Fock and Density Functional Theory Calculations

Multilocal minima on the potential energy surface (PES) of the electronic ground state (X1Σ+) of the N2O molecule are predicted by various ab initio methods. The calculations confirm that the global minimum of the molecule possesses an N−N−O linear structure with C∞v symmetry, as experiment and other theoretical calculations have recognized. The present calculations also predict other local minima on the energy surface: a less stable cyclic isomer with a C2v symmetry and a least stable linear N−O−N isomer with a D∞h symmetry. The electronic structures of the local minima indicate that the energy of the system increases if the N−N bond of the molecule becomes weak (the cyclic C2v case) or breaks (the linear D∞h case). The electronic structure and stabilities of the local minima of the N2O molecule are also discussed and analyzed using DFT calculations and wave functions, and a qualitative valence bond representation for the C∞v → C2v → D∞h isomerization is provided.

Doublet and quartet states of Li 2 −

Electronic states of the molecular lithium anion are investigated by configuration-interaction calculations. Comparison with the analogously computed potential energy curves for the lowest singlet and triplet states of the neutral Li2 shows that in addition to the well-known stable ground state X2Σ u + there also exist metastable excited states of Li 2 − . Within the quartet sector, two candidates for such long-lived states are identified and their spectroscopic properties studied.

FLUORESCENCE EXCITATION SPECTRUM OF B2Σ＋—X2 Σ+ OF AlO RADICAL IN A SUPERSONIC JET

Laser-induced fluorescence excitation spectrum of B2Σ＋— X2Σ+ transition of gas-phase AlO radical cooled in a supe rsonic jet has been observed in the range of 430—480nm.AlO was produced by reac ting O2 with Al atoms from a dc discharge-sputtering source.The obser ved vibrational bands were identified as V′-V″=1,2,3 transitions respectively. The vibrational frequencies and anharmonic constants were obtained for both the ground state X2Σ+ and the excited state B2Σ+.Furthermore a rotational analysis of the (1,4) band was made.The abno rmal intensity of the V″=5 transitions is discussed.

Numerical Pattern Recognition Analysis of CO Atmospheric Simulation Experiments

A technique entitled Hybrid Linear Pattern Analysis (HLPA), which represents a combination of model-based and pattern recognition-based approaches to the analysis of spectroscopic data, is introduced and applied to the analysis of time-resolved infrared emission spectra of ground electronic state (X1Σ+) CO obtained in atmospheric simulation experiments. The spectra are highly congested and consist of incompletely resolved, overlapping v‘ − v‘ ‘ = 1 emission bands from v‘ = 1 up to at least v‘ = 12. The analysis of the time dependence of the emission intensity in the various vibrational bands had been stymied by a severe optical opacity effect in the v = 1 → 0 emission, which is difficult to simulate; thus, conventional least-squares fitting could not be used confidently to determine the time-dependent emission intensity of this band, or that of at least three other emission bands that overlap strongly with it. The HLPA technique permits an alternate approach in which the v = 1 → 0 emission band is considered to be an unknown pattern that is identified by the Extended Cross Correlation (XCC) pattern recognition technique (J. Chem. Phys. 1997, 107, 8349). The intensity profiles of the other bands, however, can be predicted accurately based on the experimental parameters, and this knowledge is used in conjunction with the results of the XCC to determine the time dependence of all of the vibrational bands, and the intensity profile of the v = 1 → 0 emission band.

Laser-Excited Fluorescence Spectra of Yttrium Monoiodide

The rotational structure of the laser-excited fluorescence of yttrium monoiodide, recorded on a Fourier transform spectrometer, was analyzed, enabling the characterization of two excited states at Te ∼ 20 690 and ∼24 100 cm−1. Observation of the ground state X1Σ+ is extended up to v = 15. A scheme for the electronic structure is proposed, involving the X1Σ+, B1Π, D1Π, Ω1, and possibly A(1Δ) states.

THE ANGULAR MOMENTUM ORIENTATION OF C2H221 AND ITS COLLISIONAL DECAY AND TRANSFER

The rotational angular momentum orientation of acetylene in vibrationally excited discrete rotational state (X1Σ+g，ν″2＝1，J″) has been selectively prepared by circularly polarized laser stimulated Raman pumping. From the induced fluorescence by a circularly polarized UV laser, A1Au(ν′3＝1)←X1Σ+g(ν″2＝1), the orientation of C2H2(X1Σ＋g，ν″2＝1，J″＝4，7，8，…，13）is measured for the first time. The decay rate constants and transfer of the orientation from the initial excited level to neighboring rotational states have been extracted.

Bound electronic states X1Σ+, a3Π and A1Π of C2B-

Large-scale electronic structure calculations were performed to generate a three-dimensional potential energy function for the X1Σ+ state of C2B-. Spectroscopic constants and anharmonic ro-vibrational levels were calculated variationally and by perturbation theory using this function. The ground state possesses an equilibrium geometry with ReCC=1.270 Aand ReCB=1.461 A, the fundamental vibrational transitions are predicted at ν1CB(J=0)=1014.7 cm-1, ν2(J=1)=125.4 cm-1 and ν3CC(J=0)=1935.4 cm-1 (exp. 1936.3 cm-1). The difference electron density plot showed that the negative charge is almost entirely localized in the boron lone pair and the BC bond region. The A1Π–XΣ+Te excitation energy was calculated to be 23722 cm-1 confirming the assignment made for the transition detected at T0=23131 cm-1 in a neon matrix. For the A1Π state an equilibrium geometry with ReCC=1.324 Aand ReCB=1.396 Awas obtained. The vertical excitation energy of the a3Π–X 1Σ+ transition is predicted at 15306 cm-1. Both excited states lie below the vertical detachment energy calculated at 25845 cm-1.

Dissociative recombination of HeH + . I. Rovibrational spectrum of HeH Rydberg states

The repulsive ground electronic state X2Σ+ of HeH is strongly coupled to the Rydberg states at small interatomic distances. Such large couplings also occur between some of the Rydberg states. HeH+ ions that capture an electron in a Rydberg state end up in separated He and H atoms by indirect predissociation. This paper presents a study of potential functions and pertinent matrix elements involving the lowest electronic states: the 2Σ+ states, X, A, C, and D, and the 2Π states B and E. Individual transition rates as well as total radiative and non-radiative lifetimes have been computed for the lowest vibrational and rotational levels.

On the Singlet Spectrum of ZrS

Three electronic transitions in the singlet manifold of the zirconium sulphide (ZrS) molecule have been rotationally analyzed. They are the B1Π–X1Σ+, C1Σ+–X1Σ+, and E1Σ+–X1Σ+systems with (0,0) band heads at 924.60, 731.51, and 494.47 nm, respectively. The ground state X1Σ+has an equilibrium bond distance of 2.15661(4) Å. Perturbations in the B1Π and C1Σ+states are discussed.

Relative Band Oscillator Strengths for Carbon Monoxide: [ITAL]A[/ITAL] [TSUP]1[/TSUP]Π–[ITAL]X[/ITAL] [TSUP]1[/TSUP]Σ[TSUP]+[/TSUP] Transitions

Band oscillator strengths for CO transitions between the electronic states A1Π and X1Σ+ were measured via absorption with a synchrotron radiation source. When referenced to the well-characterized (5, 0) band oscillator strength, our relative values for the (7, 0) to (11, 0) bands are most consistent with the recent experiments of Chan et al. and the theoretical predictions of Kirby & Cooper. Since the results from various laboratory techniques and theory now agree, analyses of interstellar CO based on absorption from A-X bands are no longer hindered by uncertainties in oscillator strength.

The Fourier Transform Infrared Spectrum of PN

The infrared absorption spectrum of the PN molecule has been recorded for the first time using an FTIR spectrometer. A flowing discharge of PCl3 and N2 was used to produce short-lived PN molecules at room temperature in a long-path cell. Spectra of the fundamental transition were recorded at a nominal resolution of 0.02 cm−1 and calibrated against accurately known water vapor lines present in the background to give an absolute and relative accuracy on the order of 0.0004 cm−1. The line positions measured in this work were analyzed in terms of effective band constants and combined with previous high-temperature microwave and infrared data to produce accurate spectroscopic parameters for the ground state X1Σ+.

On the emission spectrum of HfS

The microwave induced emission spectrum of gaseous HfS has been studied in the region 11 000-21 000 cm−1. Six band systems, not previously observed, have been photographically recorded in grating spectrographs and rotationally analysed. Five of the transitions terminate on a common lower state, the X1Σ state. The five upper states are in energy order the A1Σ, B1Π, D1Π, E1Π and F1Σ states. The sixth system, located between the B-X and D-X systems, is perturbed and is identified as the sulphide counterpart to the hafnium oxide system called C. Also, the three analysed lowest vibrational levels of the F1Σ state are perturbed. Accurate molecular constants of the five regular states, the X, A, B, D, and E states, have been determined using the direct approach method. Only the most abundant isotopomer Hf180S32 is treated.

Fourier transform spectroscopy of LaCl: rotational analyses of the infrared band systems

Thermal emission spectrum of the LaCl molecule has been observed for the first time, the spectrum has been studied in high resolution using a Fourier transform spectrophotometer. Two singlet and two triplet band systems in the infrared region have been rotationally analyzed. The two singlet systems centered at 5958 cm−1 and 9557 cm−1 are shown to have a common lower state and are characterized as 1Π–1Σ and 1Σ–1Σ transitions, respectively. The common lower state is probably the ground state X1Σ+ in analogy with LaF [13] and YCl [11]. The two triplet systems centered at 7250 cm−1 and 10 650 cm−1 also have a common lower state and are here designated as 3Φ–a3Δ and 3Δ–a3Δ transitions, respectively. Molecular constants for the involved states have been determined.

Stability of highly excited electronic states of Be+2

Multireference configuration interaction calculations on about 40 electronic states of Be+ 2 are reported. The ground state X2Σ+ u (σ2 gσu) is bound, with R e = 4·25 a 0, ωe = 513 cm-1 and D e = 1·94 eV. Excited states showing a stronger bonding arise from the excitations σu → πu (12Πu) and σgσu → π2 u(4,2Σ- g, 2Σ+ g, 2Δg). Doubly excited 14Σ- g has the shortest R e (3·43 bohr), highest ωe (816 cm-1) and largest D e (4·16 eV) so far reported for any diatomic Be species. The existence in Be+ 2 of several strongly bound, doubly excited states is caused by the low energy of Be(sp) + Be+ (p) products. Most of the low-lying Rydberg members 3s, 3p and 3d of Be+ 2 have irregular potential curves (double-minima) because of avoided crossings with valence species. The Rydberg species 22Δg(σu → 3dδg), however, has a regular potential curve. The ionization potentials and Franck-Condon factors for Be2 → Be+ 2 transitions are reported. The adiabatic ionization potentials resulting from σu → ∞ (X1Σ+ g → X2Σ+ u) appears ...

Ab initio studies of ground and excited electronic states of MgAr, CdAr, and BeAr

The ground state (X 1Σ+) and several excited state (A 3Π,c 3Σ+,C 1Π,D 1Σ+, andE 3Σ+) potential energy surfaces for the diatomic molecules MgAr, CdAr, and BeAr have been computed using complete active space self-consistent field (CASSCF) wavefunctions and valence double- and triplezeta quality basis sets augmented with polarization and diffuse functions. Pump-and-probe laser experiments have examined the quenching, of excited singlet states of metal-rare gas complexes such as CdXe to produce triplets that dissociate to3 P Jmetal atoms. This quenching, which is detected for CdXe but not for CdAr or MgAr, is thought to occur via a crossing or strong coupling of a repulsive triplet curve correlating to the underlying3 P state of the metal, with an attractive singlet curve that correlates to the higher1 P state of the metal. The present work indicates that the attractiveC 1Π and repulsivec 3Σ+ curves of MgAr and CdArdo not intersect in the energetically accessible region of theC 1Π surface, unlike the corresponding curves for the CdXe diatom. These data are consistent with the absence of3 P J Cd atoms in the MgAr and CdAr experiments, respectively. However, an alternative quenching mechanism involving “vibronic” coupling between theC 1Π vibrational eigenstates and the continuum eigenstates of the underlying repulsive3Σ+ surface may be operative; this possibility is examined qualitatively and predicted to be unlikely for MgAr (due to small spin-orbit coupling) and CdAr (due to unfavorable vibronic factors). BeAr, which has yet to be probed experimentally, is predicted to be bound by 770 and 900 cm−1 in theD 1Σ+ state (which has metal 2s2p character) and theE 3Σ+ state (which has Rydberg metal 2s3s character), respectively, and to display interesting potential curve intersections.

Further analyses of laser induced fluorescence and emission spectra of YF: New constants for the ground X1Σ state up to ν = 10

The (ν′ = 6)-(ν″ = 1, 2, 3, 5, 7, 9, 10), (ν′ = 5)-(ν″ = 2, 8) and 4-1 bands of the C1 Σ-X1Σ system observed in the fluorescence spectra and the emission 0-0 and 0-1 bands of the same system of the YF molecule were analyzed. Following rotational analyses, the molecular constants for the ground X1Σ state up to ν = 10 were calculated from a simultaneous multiband fitting. The analyses of two fluorescence series of bands revealed new orbitally degenerate states with energies T(J = 62) = 33851 and T(J = 57 ± 1) = 12683·6 cm-1 and T(J = 61 ± 1) = 14421·6 cm-1. The last levels seem to belong to the b3Π2 (ν = 0 and ν = 3) component.

Observation of the 39K2 a 3Σ+u state by perturbation facilitated optical–optical double resonance resolved fluorescence spectroscopy

Rydberg states of the potassium dimer in the 28 430–29 080 cm−1 and 30 030–30 500 cm−1 regions above the ground state X1Σ+g minimum have been studied using the perturbation facilitated optical–optical double resonance technique (PFOODR). Energy levels in these energy regions have been assigned to both triplet and singlet gerade states based on excitation pattern information as well as intensity considerations. Resolved fluorescence from a mixed triplet–singlet 43Πg ∼1Πg upper state to the ground triplet state a 3Σ+u has been used to construct a potential energy curve for the a 3Σ+u state which is in excellent agreement with recent theoretical results. Since this electronic state and the ground singlet state X1Σ+g share the same dissociation limit, we have determined the dissociation energy for the potassium dimer to be De=4450±2 cm−1.

Relativistic ab initio CI study of the X1Σ+ and A1Σ+ states of the AgH molecule

A no-pair formalism employing external field projection operators correct to second order in the one-particle potential is used to calculate the potential curves in the neighborhood of the equilibrium geometry for the ground state X1Σ+ and the first excited state A1Σ+ of the AgH molecule, thereby determining equilibrium bond length and harmonic frequencies for these species. We report all electron calculations in the self consistent field (SCF) approximation and on configuration interaction (CI) level, for the non-relativistic hamiltonian operator as well as for its spin-free relativistic counterpart. The SCF results for the bond length of the ground state (rel. 169.2 pm, non-rel. 176.2 pm) are in good agreement with earlier all-electron Dirac-Hartree-Fock (DHF) calculations, and the CI results (rel. 162.1 pm, non-rel. 169.7 pm) show the relativistic contribution to the bond length contraction including correlation and can be compared with the experimental value of 161.8 pm.