The A1Σ+-X1Σ+ band system of the KH and KD molecules

The molecular constants of the A¹Σ⁺ and X¹Σ⁺ states of the KH and KD molecules have been determined using mass relations correspondent to a normal isotope shift. For the calculation we have used data of the laser-induced fluorescence spectrum by the Ar⁺ 4881 Å exciting line photographed in our laboratory, as well as previous data presented by other authors. From the spectroscopic terms, quantum-mechanical PMO-RKR-van der Waals hybrid potentials have been generated. Numerical calculations for the A¹Σ⁺ and X¹Σ⁺ states of the KH and KD species are comapred with quantum-mechanical values obtained by numerical solution of the radial Schrödinger equation. Vibrational wavefunctions appropriate to the potential curves yield values of E_υ and B_υ which are in close agreement with the experimental results. The probability distribution functions and Franck-Condon factors for the A¹Σ⁺ ↔ X¹Σ⁺ band system have also been determined. It is observed that the anomalous behaviour of the A state is clearly revealed with a changed anharmonicity for the lowest vibrational levels.     

New self-consistent potentials for the X1Σ+ and A1Σ+ states of KH

The vibrational and rotational molecular constants have been determined for the A¹Σ⁺  X¹Σ⁺ system of the isotopic potassium hydrides: KH and KD. From these experimental term values, isotopically combined PMO-RKR-van der Waals potentials are constructed, which are checked by direct integration of radial Schrödinger equation. As an additional check on the accuracy of the potentials, the wavefunctions were used to compute B_ν, D_ν, H_ν and L_ν values. The agreement between the calculated and experimental results is quite satisfactory. Franck-Condon overlap integrals and probability density distributions have been calculated. The anomalous behaviour of the A¹Σ⁺ state may be observed in the probability density functions of the lowest vibrational levels.     

BH分子X 1Σ+、A 1Π和B 1Σ+ 态的势能函数

利用SAC/SAC-CI方法，使用D95++、6-311++g及cc-PVTZ等基组，对BH分子的基态(X ¹Σ⁺)、第一简并激发态(A ¹Π)及第二激发态(B ¹Σ⁺)的平衡结构和谐振频率进行了优化计算． 通过对三个基组计算结果的比较，得出了cc-PVTZ基组为三个基组中的最优基组的结论；使用cc-PVTZ基组，利用SAC的GSUM(group sum of operators)方法对基态(X ¹Σ⁺)， SAC-CI的GSUM方法对激发态(A ¹Π 和B ¹Σ⁺)进行单点能扫描计算, 用正规方程组拟合Murrell-Sorbie函数，得到了相应电子态的完整势能函数；从得到的势能函数计算了与基态(X ¹Σ⁺)、第一简并的激发态(A ¹Π)和第二激发态(X ¹Σ⁺)相对应的光谱常数(Be、αe、ωe 和ωeχe)，结果与实验数据较为一致． 其中基态、第一激发态与实验数据吻合得较好．     

LiH分子X 1Σ+ 、A 1Σ+和B 1Π态的势能函数

The energies, equilibrium geometries and harmonic frequencies of the three electronic states (the ground state X 1Σ+, the first excitation state A 1Σ+ and the second excitation degenerate state B 1Π) of LiH molecule have been calculated by using the GSUM (Group Sum of Operators) method of SAC/ SAC-CI with the basis sets D95(d), 6-311G**, and cc-PVTZ. Comparing with the above-mentioned three basis sets, the conclusion is gained that the basis set D95(d) is the most suitable for the energy calculation of LiH molecule. The whole potential curves for these three electronic states are further scanned, using SAC/D95(d) method for the ground state and SAC-CI/D95(d) methods for the excited states. Murrell-Sorbie function were fitted using a least square and then the spectroscopy constants are calculated, which are in good agreement with the experimental data.     

Self-consistent potential energy curves for the A1Σ+ and X1Σ+ states of isotopic cesium hydrides

From the spectroscopic experimental data available in the literature we have determined the mass-reduced Dunham coefficients for the A¹Σ⁺ ↔ X¹Σ⁺ system of the isotopic species CsH and CsD. Based upon these results, for both ground and excited states of cesium hydride and deuteride we report new hybrid rotationless potential energy curves (PMO-RKR-van der Waals) up to the dissociation. As a consistency check on the accuracy of the potentials the eigenvalues were calculated by direct numerical integration of the radial Schrödinger equation and found to agree within the rms error 0.39 cm⁻¹ (X¹Σ⁺) and 0.41 cm⁻¹ (A¹Σ⁺) with the experimental vibrational energies. From the wavefunctions, the rotational constants B_υ, centrifugal distortion terms D_υ, H_υ and L_υ, Franck—Condon factors, and probability density distributions were obtained. The probability density distributions for the lowest vibrational levels of the A¹Σ⁺ show an anharmonicity associated with the anomalous behavior of that state.     

The potential energy curves and probability density distributions of the X1Σ+ and A1Σ+ states of RBH

The potential energy curves PMO—RKR—van der Waals of the electronic A¹Σ⁺ and X₁Σ⁺ states of RbH have been determined. The potentials obtained are self-consistent with the experimental data because they have been tested by direct numerical solution of the radial Schrödinger equation. From exact vibrational eigenfunctions probability density distributions and Franck—Condon factors have been calculated over the range of vibrational levels observed. It is observed that the anomalous behaviour of the A¹Σ⁺ state arises in the υ′ = 1, 2 and 3 levels with probability density functions similar to those of a harmonic oscillator.     

BF分子X~1Σ~+,A~1Π和B~1Σ~+电子态的势能函数

使用SAC/SAC-CI和D95++,6-311++g,6-311++g**及D95(d)基组,分别对BF分子的基态X~1Σ~+、第一简并激发态A~1Π和第二激发态B~1Σ~+的平衡结构和谐振频率进行优化计算.对所有计算结果进行比较,得出6-311++g**基组为最优基组.运用6-311++g**基组和SAC方法对基态X~1Σ~+,SAC-CI方法对激发态A~1Π和B~1Σ~+进行单点能扫描计算,并用正规方程组拟合Murrell-Sorbie函数,得到相应电子态的势能函数解析式,由得到的势能函数计算了与X~1Σ+,A~1Π和B~1Σ~+态相对应的光谱常数,结果与实验数据较为一致.     

Analysis of the long range potentials of the X 1Σ+ and a 3Σ+ states of NaK

The difference in energy between the singlet and triplet states of NaK dissociating to Na(3s) and K(4s) is found from experimental data and from pseudopotential calculations. The contributions of various one- and two-electron integrals are evaluated, illustrating the present ambiguity over the exchange integral and the exchange interaction terms.     

The a3Π0+,1-X1Σ+ emission systems of SnH+

New visible emission systems have been observed from the helium afterglow reaction of SnH₄. On the basis of the rotational analysis, they were interpreted as the a³Π_0⁻-X¹Σ⁺ and a³Π₁-X¹Σ⁺ subsystems of SnH⁺. Spectroscopic constants have been obtained for the a³Π_0⁺ and X¹Σ⁺ states.     

HF(B1Σ→X1Σ) UV chemiluminescence from the H+/H+2+F− ion-ion reactions

Chemiluminescence spectra attributable to the H⁺/H⁺₂+F⁻→ HF B¹Σ ion-ion reactions were obtained in the wavelength region 185–270 nm. The rovibrationally resolved bands were assigned as HF B ¹Σ (v', J') to HF X ¹Σ (v″,J″) transitions with 0⩽v'⩽4 and 12 ⩽ v″ ⩽ 16. The corresponding rotational branches all have peaks at high J values. These non-thermal distributions suggest that the corresponding product state v',J' populations reflect the nascent distribution from the ion-ion reactions.     

Resonance Raman scattering in the 1Σg+ → 1B2 (1Σu+) transition of CS2

Resonance Raman spectra of CS₂ are presented at excitation wavelengths of 204 and 200 nm. Both spectra show activity in the symmetric (ν₁) stretch and bending (ν₂) modes consistent with a bent, symmetrically stretched ¹B₂(¹Σ_u⁺) upper state. In addition, these spectra show activity of the transition involving two quanta in the asymmetric (ν₃) stretch as well as progressions in ν₁ and ν₂ based upon this asymmetric mode overtone.     

Fourier spectrometry investigation of the 1 3Σg+ →a 3Σu+ transition of the 7Li2 molecule

The 1 ³Σ_g⁺ → a ³Σ_u⁺ transition in the ⁷Li₂ molecule has been observed in the 8200–10 000 cm⁻¹ region with a high resolution Fourier spectrometer. Rotational analysis of 1 ⩽ υ′ ⩽ 7 of 1 ³Σ_g⁺ and 0 ⩽ υ″ ⩽ 7 of a ³Σ_u⁺ has been carried out. We found D_e(a ³Σ_u⁺) = 332.5 ± 1.0 cm⁻¹ that gives T_e(a ³Σ_u⁺) = 8184.3 ± 1.5 cm⁻¹ and D_e(1 ³Σ_g⁺) = 7090.4 ± 1.5 cm⁻¹ with T_e = 16330 ± 2 cm⁻¹.     

Rotationally resolved (3 + 1) rempi of H 2 via the B1Σ+u state

In the paper, we compare the results of our ab initio calculations for the ro-vibrational branching ratios resulting from a (3+1) REMPI of H₂ via the B¹Σ⁺_u state with the experimental data of Pratt, Poliakoff, Dehmer and Dehmer. These results indicate that non-Franck-Condon effects are less important here than in the (3+1) REMPI of H₂ via the C¹Π_u state. We observe that the ΔJ = ±3 peaks in the photoelectron spectrum are of negligible strength and that the ratio of ΔJ = +1 to ΔJ = −1 peak is independent of the ionic vibrational state. A detailed analysis indicates that these features arise as a result of a dynamic interference between the do and dμ ionization channels and do not imply either the smallness of the d-wave or the smallness of the j_t = 3 angular momentum coupling terms.     

Rotational analysis and deperturbation of the A2Π → X2Σ+ and B'2Σ+ → X2Σ+ emission spectra of MgH

Deperturbation analysis of the A(2)Π → X(2)Σ(+) and B(')(2)Σ(+) → X(2)Σ(+) emission spectra of (24)MgH is reported. Spectroscopic data for the v = 0 to 3 levels of the A (2)Π state and the v = 0 to 4 levels of the B'(2)Σ(+) state were fitted together using a single Hamiltonian matrix that includes (2)Π and (2)Σ(+) matrix elements, as well as off-diagonal elements coupling several vibrational levels of the two states. A Dunham-type fit was performed and the resulting Y(l,0) and Y(l,1) coefficients were used to generate Rydberg-Klein-Rees (RKR) potential curves for the A (2)Π and the B'(2)Σ(+) states. Vibrational overlap integrals were computed from the RKR potentials, and the off-diagonal matrix elements coupling the electronic wavefunctions (a(+) and b) were determined. Zero point dissociation energies (D(0)) of the A(2)Π and B'(2)Σ(+) states of (24)MgH were determined to be 12,957.5 ± 0.5 and 10,133.6 ± 0.5 cm(-1), respectively. Using the Y(0,1) coefficients, the equilibrium internuclear distances (r(e)) of the A(2)Π and B'(2)Σ(+) states were determined to be 1.67827(1) ? and 2.59404(4) A?, respectively.     

Bound vibrational levels of the two lowest 1Σ+ states of LiF

The energies of the vibrational levels of the two lowest ¹Σ⁺ states of LiF corresponding to adiabatic and to diabatic potential energy curves are calculated and compared. The high-lying levels of the ionic adiabatic and diabatic states separating to Li⁺ + F^- are represented by quantum defect formulas.     

Accurate electrical and spectroscopic properties ofX 1Σ+ BeO from coupled-cluster methods

Summary This paper reports a series of coupled-cluster (CC) calculations through CCSDT on the theoretically challenging ground state of the BeO molecule. Along with CC methods, quadratic configuration interaction (QCI) approximations to CC theory have been used (QCISD and QCISD(T)), which show several dramatic failings. Equilibrium electrical properties (, _xx , and _zz ) and basic spectroscopic properties (r _e, _e,D _e, and infrared intensity (I)) have been computed. Basis set and electron correlation effects are analyzed in order to arrive at accurate values of the dipole moment and polarizability, which are not known experimentally. For the dipole moment, we obtain a value of 6.25 D, with an uncertainty of about 0.1 D. For _xx and _zz , we suggest respective values of 32 and 36 atomic units (a.u.) and error bars of about 1 and 2 a.u. With extended basis sets, the spectroscopic propertiesr _e, _e, andD _e are reproduced to high accuracy, which is the first time this has been achieved for this species byab initio methods. At the highest calculation levels,I is predicted to be very small. AlthoughI has not been measured, some support for this prediction comes from a recent infrared study of BeO-rare gas complexes. The QCI methods are shown to be much more sensitive to basis set, and even with large basis sets yield values of _zz andI which differ from CC results by an order of magnitude and three orders of magnitude, respectively. These differences doubtless arise from the importance of single excitations (T ₁) for this molecule, as several terms involvingT ₁ are neglected in the QCISD approximation compared with CCSD. We also report CC calculations with Brueckner orbitals, which yield results similar to those obtained with restricted Hartree-Fock orbitals.     

The X1Σ+ ground state of kh near the dissociation limit

Fluorescence excited in the A¹Σ⁺ -X¹Σ⁺ system of ³⁹KH by the 4880 Å argon-ion laser line gives information about the ground state as far as the last bound rovibrational level. This is identified as J = 6 in v = 23, and, assuming a limit midway between J = 6 and J = 7, D_e(KH) = 14776 ± 4 cm⁻¹.