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.     

N2+分子离子的B2Σu+、A2Πu和X2Σg+电子态光谱研究

采用光外差-磁旋转-速度调制吸收光谱技术, 在可见光波段范围16800～17573 cm-1, 对N2+的A 2Πu-X 2Σ+g(12,6)、(11,5)、(7,2)带和B 2Σ+u-X 2Σ+g (1,5)带进行了测量和分析,推导了双原子分子振转能级在受到微扰作用时的有效哈密顿量形式,并分析了N2+的A 2Πu-B 2Σ+u之间存在的微扰相互作用,通过与实验数据的拟合得到了精确的电子态微扰常数ξe、ηe .     

Adiabatic calculations of the 2Σ+g excited states of He+2

The first six ²Σ⁺_g adiabatic potential energy curves of He⁺₂ are calculated with the MRD CI method employing configuration selection (T = 10 μ hartree) and perturbative energy corrections and using two basis sets differing in the number of diffuse functions. The non-adiabatic matrix elements at the numerous avoided crossings are also calculated and approximate diabatic curves are constructed. Various aspects of the results are discussed.     

Perturbations in the CN(B 2Σ+−X 2Σ+) tail band system. Vibrational assignment of the B 2Σ+ ∼ 4Π perturbation

The quantum numbers of the vibrational levels for the ⁴Π state which perturb the ν_B = 14 and 17 levels of the B ²Σ⁺ state are assigned by an analysis of the vibrational dependence of the B ²Σ⁺ ∼ ⁴Π perturbation constants. The vibrational levels involved in the B ²Σ⁺ ∼ ⁴Π perturbation, (ν_B, ν_Π) = (9, 1), (12, 4), (14, 7), (17, 12), and (18, 14), are consistent with the results of our recent ab initio calculation.     

Electric dipole moments of the MgO B1Σ+ and X1Σ+ states

The electric dipole moment of the excited B¹∑⁺ (υ′ = 0) state of MgO produced in a gas-phase reaction of Mg(¹S) atoms and N₂O is measured using the technique of Stark quantum-beat spectroscopy. It is shown to be |μ_υ′=0| = 5.94(24) D. The lifetime of the excited B¹∑⁺ (υ′ = 0) state is determined as τ = 22.5(1.5) ns. Using laser excitation spectroscopy and by direct observation of the P(1) line splitting at high electric field strengths in the B¹∑⁺−X¹∑⁺ (0,0) system the ground state electric dipole moment is measured yielding |μ_υ=0| = 6.2(6) D. Furthermore an electric-field-induced Q branch is observed.     

Alignment effect of N2(A3Σu+) in the energy transfer reaction of aligned N2(A3Σu+) + NO(X2Π) → NO(A2Σ+) + N2(X1Σg+)

Steric effect in the energy transfer reaction of N(2)(A(3)Σ(u)(+)) + NO(X(2)Π) → NO(A(2)Σ(+)) + N(2)(X(1)Σ(g)(+)) has been studied under crossed beam conditions at a collision energy of ~0.07 eV by using an aligned N(2)(A(3)Σ(u)(+)) beam prepared by a magnetic hexapole. The emission intensity of NO(A(2)Σ(+)) has been measured as a function of the magnetic orientation field direction (i.e., alignment of N(2)(A(3)Σ(u)(+))) in the collision frame. A significant alignment effect on the energy transfer probability is observed. The shape of the steric opacity function turns out to be most reactive at the oblique configuration of N(2)(A(3)Σ(u)(+)) with an orientation angle of γ(v(R)) ~ 45° with respect to the relative velocity vector (v(R)), which has a good correlation with the spatial distribution of the 2pπ(g)* molecular orbital of N(2)(A(3)Σ(u)(+)). We propose the electron exchange mechanism in which the energy transfer probability is dominantly controlled by the orbital overlap between N(2)(2pπ(g)*) and NO(6σ).     

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.     

Comment on “ab initio investigation of low-lying 2Σ+ and 2Π states of NO2+”

Energies of the singlet stales of the doubly charged nitric oxide cation have been determined experimentally by the technique of double charge transfer, and are compared with previous results of full-valence MC SCF plus first-order CI techniques. The good agreement obtained permits an assignment of some of the peaks in the experimental spectrum, and confirms the accuracy of these calculations.     

The X2Σ+ state of LiCa studied by Fourier-transform spectroscopy

The paper reports on a successful observation of high resolution Fourier transform spectra of LiCa. The fine structure of the ground state was observed and attributed to effective spin-rotation interaction. The experimental observations are described by two models using potential energy curves. One of them takes into account the fine structure splitting by means of effective constants, the other by means of a R dependent function γ(R), built in the radial Schr?dinger equation. Ab initio calculations were performed for γ(R) which comes close to the experimental function.     

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.     

Prediction of the rovibrational emission spectroscopy of B2Σ(+)-X2Σ(+) system in 12C17O+

An analytical formula based on the Herzberg's conventional rovibrational energy levels for diatomic system is proposed by taking multiple differences of spectral lines to predict the R-branch high-lying rovibrational emission spectroscopy, where only 15 accurate known transition lines and rotational constants D(v'), D(v') are needed. Using the formula, the R(11ee) and R(22ff) branches of (0, 2) and (0, 3) transition bands in the B(2)Σ(+)-X(2)Σ(+) system of (12)C(17)O(+) are studied. The results show that not only the relatively lower order rovibrational transition lines given by experiments are reproduced but also the higher and the absent spectral lines are correctly predicted for each band.     

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.     

(2+1) REMPI of NO via the D 2Σ+ state: rotational branching ratios

Recent photoelectron spectroscopic studies in a (2 + 1) REMPI of NO via the Rydberg D²Σ⁺ state have revealed anomalous ionic rotational branching ratios. We have performed ab initio calculations of these branching ratios and find that the molecular nature of the ionization continuum plays an essential role in the dynamics. Even though the bound orbital is very atomic-like (⪢ 98% p-like), the photoelectron continuum wavefunction is quite sensitive to the non-spherical nature of the molecular ionic potential and causes a strong persistence of the p-partial wave which, in turn, leads to a large ΔN = 0 peak.     

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.     

Decay of the A2Σ+ and B2II quasibound states of HeH

The X²Σ⁺, A²Σ⁺ and B²II wavefunctions of the HeH molecule are calculated as single configurations state functions built from molecular orbitals generated by the Fock operator of the HeH⁺ ion. Dipole transition moments and non-adiabatic coupling matrix elements are evaluated in order to study the competition between dissociative photoemission and predissociation of the A and B states. Particular attention is paid to the X-A (2σ–3σ) avoided crossing and comparisons are made between its characteristics and those of the corresponding 2¹Σ⁺–3¹Σ⁺ (2σ–3σ) avoided crossing in the HeH⁺ ion. The predissociation lifetime of the A state is found to be of the order of 10⁻¹³ s which precludes its decay via dissociative photoemission in agreement with the analysis of recent translational spectroscopy experiments. The predissociation lifetime of the B state is found to be of the same order of magnitude as its radiative lifetime (i.e. of the order of a few 10⁻⁸ s). It is still not understood why this state would radiate rather than predissociate as has been inferred from experiment.     

Nonadiabatic quantum reactive scattering of the OH(A 2Σ+) + D2

The seams of conical intersection exist between the ground (1 (2)A(')) and the first-excited (2 (2)A(')) electronic potential energy surfaces (PESs) of OH(A (2)Σ(+),X (2)Π) + H(2) system. This intersection induces the nonadiabatic quenching of OH(A (2)Σ(+)) by D(2). We present nonadiabatic quantum dynamics study for OH(A (2)Σ(+)) + D(2) on new five-dimensional coplanar PESs. The ab initio calculations of PESs are based on multireference configuration interaction (MRCI)/aug-cc-pVQZ level. A back-propagation neural network is utilized to fit the PESs and nonadiabatic coupling. High degrees of rotational excitation of quenched OH(X (2)Π) products are found in nonreactive quenching channel, and the quenched D(2) products are vibrationally excited up to quantum number v(2) (')=8. The theoretical results of nonadiabatic time-dependent wave-packet calculation are in good agreement with the existing experimental data.     

The (1) 3Σg+ electronic state of Cs2

Laser-induced fluorescence of Cs₂ molecules, recorded by high-resolution Fourier spectroscopy, has been used for the first spectroscopic identification of the lowest gerade triplet (1) ³Σ_g⁺ electronic state. This state can be described by the molecular parameters: T_e = 11602.10 cm⁻¹, B_c = 8.258×10⁻³ cm⁻¹, D_c = 2.56×10⁻⁹ cm⁻¹ and R_c = 5.5425 Å. Determination of the absolute vibrational numbering will require further experiments.     

Experimental characterization of the CN X 2Σ+ + Ar and H2 potentials via infrared-ultraviolet double resonance spectroscopy

The hindered internal rotor states (n(K) = 0(0), 1(1), and 1(0)) of the CN-Ar complex with two quanta of CN stretch (v(CN) = 2), along with its ground state (v(CN) = 0), have been characterized by IR-UV double resonance and UV spectroscopy. Analysis of rotationally structured bands enable n(K) assignments and reveal perturbations due to Coriolis coupling between two closely spaced hindered rotor states, n(K) = 1(1) and 1(0). A deperturbation analysis is carried out to derive accurate rotational constants and their associated CN center-of-mass to Ar bond lengths as well as the magnitude of the coupling. The energetic ordering and spacings of the CN-Ar hindered rotor states provide a direct experimental probe of the angular dependence of the CN X (2)Σ(+) + Ar potential and permit radially averaged anisotropy parameters (V(10) = 5.2 cm(-1) and V(20) = 3.2 cm(-1)) to be determined. This analysis indicates a relatively flat potential about a linear N≡C-Ar configuration with a barrier to CN internal rotation of only ~12 cm(-1). The angular potentials determined from experiment and ab initio theory are in good accord, although theory predicts a higher barrier to CN internal rotation. A similar approach yields the infrared spectrum of H(2)-CN in the CN overtone region, which exhibits a rotationally resolved Σ ← Σ parallel band that is consistent with theoretical predictions for ortho-H(2)-CN.     

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．