New spectroscopic analyses and potential energy curves for the X1Σ+ and A1Σ+ states of NaH

The emission spectrum of NaH has been photographed in the ～6000–7300-Å region. Additional bands of the A¹Σ⁺ electronic transition have been analyzed and in particular the observed vibrational structure of the excited A state has been extended down to v′ = 0. New spectroscopic constants have been obtained, the v′ = 0 data leading to especially large changes in the constants of the anomalous A¹Σ⁺ state. New Rydberg-Klein-Rees (RKR) potential energy curves have been calculated up to v″ = 8 of the X¹Σ⁺ state and up to v′ = 20 in the A¹Σ⁺ state.     

Fine structure of the close-lying A 2Π and B 2Σ+ states of BaH and BaD

Molecular parameters for the close-lying and strongly interacting A ²Π and B ²Σ states of BaH and BaD have been re-evaluated by means of a numerical matrix diagonalization procedure. The results obtained according to this exact method deviate considerably from the effective ones of previous investigations, particularly with respect to the A ²Π-B ²Σ⁺ interaction matrix elements which describe the large Λ-doubling and spin-splitting. The new values of the Λ-doubling and spin-splitting parameters are in excellent agreement with pure precession values for L = 2, and thus the present results form an interesting extension of the pure precession model which so far has been found applicable in a number of cases for which L equals one. The pure precession result L = 2 indicates that the outermost electron of the A ²Π and B ²Σ⁺ states must be a d-electron, and this requires a re-assignment of the configuration quantum numbers of these states. Strong local perturbations are observed in the rotational levels of the A ²Π state of both BaH and BaD, and the result L = 2 now yields a further confirmation of the previous assumption that a ²Δ state causes these perturbations. In the case of BaD the electronic + vibrational energy and the rotational constants (B_v , D_v ) of the perturbing level could be determined from the perturbed A ²Π term values, and in particular the value of the interaction matrix element leads to the conclusion that there is a A ²Π, v = 0 - ²Δ, v = 2 interaction. Finally the influence of the A ²Π - ²Δ, Δv = 0 interaction on the A ²Π and B ²Σ⁺ molecular parameters was investigated.     

Analytical potential energy functions for the ground and some excited states of N2

The analytical potential energy functions have been calculated for the ground state X¹Σ⁺_g and four excited electronic states a¹Π_g, A³Σ⁺_u, B′³Σ^?_u and B³Π_g of N₂ molecule using the algebraic and energy-consistent methods (AM-ECM). Based on our previously published full AM vibrational energies and spectroscopic constants, the low-lying force constants f_n, the expansion coefficients a_n and the variational parameters λ in the AM–ECM potentials are determined for these states. The computed AM–ECM potential energy curve of each state is in excellent agreement with the experimental data and better than other analytical potentials.     

Theoretical study of spectral parameters for the γ and β band systems of NO for atmosphere and high temperature

Highly correlated ab initio calculations were performed for accurate determination of γ (A²Σ⁺-X²П) and β (B²П-X²П) band systems of NO molecule. Highly accurate multi-reference configuration interaction approach was used to investigate the potential energy curves (PECs) and transition dipole moment curves. We correctly and fully described their diffuse wave functions by the obvious balance between the valence and Rydberg character of the X²П, A²Σ⁺, B²П, C²П and D²Σ⁺ states. The PECs of the three states (X²П, A²Σ⁺ and B²П) by using the aug-cc-pV5Z (aV5Z) basis set for N and O atoms agreed well with the Rydberg–Klein–Rees potential. Moreover, the Einstein A coefficients were calculated to predict the lifetimes, where the vibrational bands included v′ = 0–8, v″ = 0–29 for γ system and v′ = 0–11, v″ = 0–31 for β system. The spectral line intensities of the γ and β systems for atmosphere and high temperature were provided.     

The RKR potential energy curves for the X1Σ+ and A1Σ+ states of KH

New isotopically combined spectroscopic constants were obtained for the X¹Σ⁺ and A¹Σ⁺ states of $\text{KH}\text{KD}$. These constants were used to construct new isotopically combined Rydberg-Klein-Rees (RKR) potential energy curves up to v″ = 4 of the X¹Σ⁺ state and up to v′ = 26 of the A¹Σ⁺ state.     

The RKR potential energy curves for the X1Σ+ and A1Σ+ states of RbH

The A¹Σ⁺-X¹Σ⁺ laser-excited fluorescence spectrum of RbH was observed in the 4760-to 8470-Å region, using the Ar⁺ 4765-Å exciting line, and v″ = 6–12 were observed for the first time. New spectroscopic constants were obtained for the X¹Σ⁺ and A¹Σ⁺ states of RbH. New Rydberg-Klein-Rees (RKR) potential energy curves were calculated up to v″ = 12 of the X¹Σ⁺ state and up to v′ = 14 of the A¹Σ⁺ state.     

采用二维坐标和变分方法计算磷烷阳离子的伞型振动

提出一个新的二维变分方法计算PH₃⁺(X²A₂")的对称伸缩振动(v1)和伞形振动(v2). 因为采用了对称化的笛卡尔坐标,所以动能项变得简单,同时伞形振动模式也能得到很好的反映. 相比采用经常使用的一维模型计算伞形振动,这个二维模型不需要约化质量的假设,同时也考虑了v1和v2振动模式之间的相互作用. 用二维模型对PH₃⁺首次进行了计算, 前七个能级的理论值和实验值的平均相对误差小于3 cm^{-1. 用相同的方法也计算了NH₃,结果没有PH₃+理想,说明这个方法有一定的局限性.}     

Studies of labile molecules with a tunable dye laser: Laser excitation spectrum of BrF (B3Π(0+)-X1Σ+)

The B³Π(0⁺) ← X¹Σ⁺ absorption spectrum of BrF (4850–5200 Å) has been observed by the technique of laser emission spectroscopy. Fluorescence was excited by a pulsed, scannable dye laser with a 0.1 Å bandwidth. Rotational analysis has been carried out for six bands of the v″ = 0 progression (8 ≥ v′ ≥ 3) of ⁷⁹BrF and ⁸¹BrF. Rotational constants for the B³Π(0⁺) state are reported for the first time. RKR potential energy curves for both states, and an array of Franck-Condon factors and r-centroids for the transition, have been calculated. Bands with v′ > 8 were not observed in fluorescence owing to the onset of predissociation near J′ = 28 of the v′ = 8 level. An upper limit for the ground state dissociation energy is D₀″ (BrF, X¹Σ⁺) ≤ 20 880 cm^?1.     

Ab initio calculations on the ground and excited states of InI

Potential energy curves (PECs) of the ground and the low-lying excited states of the InI molecule are computed using the internally contracted multireference singles and doubles configuration interaction with the Davidson correction (ic-MR-CISD + Q) method based on the relativistic effective core potentials (RECPs). The spectroscopic constants are obtained, including the excitation energy (T _e), the equilibrium bond distance (R _e), the dipole moment (μ_e) and the vibrational constants (ω_e and ω_e). Finally, we predict the transition dipole moments, the radiative lifetimes, and the Franc-Condon factors for the transitions of A³Π₀+ ? X¹Σ₀ ⁺ and B³Π^l ? X¹Σ₀ ⁺,. The results reveal that A³Π₀+ and B³Π_l are long-lived states with the lifetimes being of the order of microseconds.     

B2C(1A1)和BC2(2A′)的结构与解析势能函数

采用单双取代的二次组态相互作用方法，分别选用6-311++G(d,p)和6-311G(df,pd)基组，对B₂C和BC₂分子的结构进行了优化，得到这两个分子的基态结构为C_2v和C_s，基态电子状态为¹A₁和²A′，同时还得到了它们的平衡几何结构、离解能、谐振频率和力常数. 关键词： 碳化硼 Murrell-Sorbie函数 谐振频率 势能函数     

Measurement of the Raman polarizability anisotropy for the v = 1 pure rotational Raman transition in H 2 by rotational Raman spectroscopy

A combination of stimulated Raman pumping and rotational Raman spectroscopy is used to accomplish the first measurement of the polarizability anisotropy γ_11,13 (355 nm) for the S₁₁ (1) transition in molecular hydrogen H₂. Saturation of the Q₀₁(1) transition connecting the |X¹ Σ⁺ _g, v = 0, J = 1 > state to the |X¹ Σ⁺ _g, v = 1, J = 1 > state in H₂ by stimulated Raman pumping is the critical element in this experiment. The observed intensities of the rotational Raman lines for these states allow an estimate of γ_11,13 (355 nm) as 0.358 ± 0.004 ų. A comparison of this value to that obtained from fundamental ab initio calculations in H₂ also is possible for the first time.     

An ab initio investigation of the low-lying electronic states of BeH

Potential energy curves(PECs) for the ground state(X 2 Σ +) and the four excited electronic states(A 2 Π,B 2 Π,C 2 Σ +,4 Π) of a BeH molecule are calculated using the multi-configuration reference single and double excited configuration interaction(MRCI) approach in combination with the aug-cc-pVTZ basis sets.The calculation covers the internuclear distance ranging from 0.07 nm to 0.70 nm,and the equilibrium bond length R e and the vertical excited energy T e are determined directly.It is evident that the X2Σ+,A2Π,B2Π,C2Σ+ states are bound and 4Π is a repulsive excited state.With the potentials,all of the vibrational levels and inertial rotation constants are predicted when the rotational quantum number J is set to be equal to zero(J = 0) by numerically solving the radial Schr¨odinger equation of nuclear motion.Then the spectroscopic data are obtained including the rotation coupling constant ω e,the anharmonic constant ωexe,the equilibrium rotation constant Be,and the vibration-rotation coupling constant αe.These values are compared with the theoretical and experimental results currently available,showing that they are in agreement with each other.     

New observations and analyses of the laser excited fluorescence of the A1Σu+-X1Σg+ bands of the Na2 molecule

A medium power (～50 mW, 6328 Å) HeNe laser is used to excite the A¹Σ_u⁺-X¹Σ_g⁺ fluorescence of the Na₂ molecule in a crossed heat pipe oven. The spectrum in the region 5800–8500 Å is recorded both photographically (3.4 M Ebert) and photoelectrically (GaAs detector) with an emphasis on accurate relative intensities and on the observation of higher vibrational levels in the ground state close to the dissociation limit. P and R doublets in four series originating from (v′ = 14, J′ = 45), (v′ = 16, J′ = 17), (v′ = 22, J′ = 86), and (v′ = 25, J′ = 87) levels are observed and identified. The first two series, known from earlier work, are extended further to longer wavelengths to include 13 to 17 additional ground-state vibrational levels. The latter two series are observed for the first time. They originate from higher J′ levels and span a wide range of v″ levels (0 ≤ v″ ≤ 48). Effective RKR potentials for specific J″ (= 17, 45, 86, and 87) quantum numbers of the ground state are constructed and from them the true (rotationless) potential energy curve (for X¹Σ_g⁺) is derived which (a) reproduces the RKR curve previously given by Kusch and Hessel and (b) extends the curve from 5.77 to 7.26 Å (outer turning point). The dissociation energy D_e is estimated from these data to be 6022 ± 21 cm^?1.     

The A3Π(1) → X1Σ+ emission spectrum of ICl in the near infrared: Rotational analysis of bands in the v′ = 0, 1, 2, 3, 4, progressions and molecular constants for the X1Σ+ and A3Π(1) states by merging with absorption data

Ten bands of the A³Π(1) → X¹Σ⁺ emission system of I³⁵Cl, lying at wavelengths of 8180 – 10000 Å, have been analyzed rotationally in the ranges 0 ≤ v′ ≤ 4 and 6 ≤ v″ ≤ 9. Constants determined from least-squares fits of frequencies of individual bands are merged with constants derived from absorption data. RKR potentials for both states are reported, and the Franck-Condon factors for ICl (A-X) have been computed for 0 ≤ v′ ≤ 35 and 0 ≤ v″ ≤ 9.     

Theoretical study of ground and excited state potential energy surfaces for the Ca+-H2 complex

The potential energy surfaces of the Ca⁺-H₂ complex are calculated using the internally contracted multireference CI method (ICMR CI) and complete active space SCF (CAS SCF) reference wave functions. The calculations involve both the ground and the excited states correlating to (3d)²D and (4p)²P Ca⁺ terms and are carried out for C_∞v and C_2v configurations. Anisotropy of the potential surfaces has also been analysed by computing the interaction energy for some representative points as a function of the angle between the H₂ molecular axis and the Ca⁺—centre of mass of H₂ bond axis. The calculations have revealed the existence of a conical intersection of the lowest excited (3d)²B₂ potential surface with the ground state one. The obtained global energy minimum of the (3d)²B₂ potential surface lying 0.683 eV below the asymptote indicates a possible stabilization of the Ca⁺-H₂ complex towards formation of an exciplex in the (3d)Ca⁺-H₂(v = 0) collision process. The dependence of the vibrational energy levels of H₂ on the distance from Ca⁺ in the C_2v configuration has also been studied.     

Ion-electron coincidence study of the thermal He(23S) + H2 Penning reaction

A new Penning-electron-Penning-ion coincidence method is described. It is applied to the study of the thermal reaction of He(2³S) with H₂. The main results reported are separate electron energy spectra that are coincident with the three different ions formed: HeH₂⁺, HeH⁺ and H₂⁺. Based on these results it is shown that the Penning reaction of the He(2³S)/H ₂ system proceeds in two well-separated steps: (i) ionization at distances R (HeH₂) ? 6a₀ in which H₂⁺ (v) is formed in different vibrational states; and (ii) reactive collision of H₂⁺ (v) with He. For the second step the variation of the branching ratios with vibrational quantum numbers v = 0 to v = 10 is derived, and it is shown that these branching ratios may be regarded as relative vibrational-energy-dependent cross-sections for the collision of H₂⁺ (v) with He at an average relative kinetic energy of ～20 meV.     

A global potential energy surface for H2S+(X 4A′′) and quasi-classical trajectory study of the S+(4S) + H2(X1Σ+g) reaction

A novel global potential energy surface for H₂S⁺(X?⁴A″) based on accurate ab initio calculations is presented. Energies are calculated at the multi-reference configuration interaction level with Davidson correction using aug-cc-pVQZ basis set plus core-polarisation high-exponent d functions. A grid of 4552 points is used for the least-square fitting procedure in the frame of a many-body expansion. The topographical features of the new potential energy surface are here discussed in detail. Such a surface is then employed for dynamic studies of the S(⁴S) + H₂(X?¹Σ⁺_g) →SH⁺(X?³Σ^?) + H(²S) reaction using the quasi-classical trajectory method. State specific trajectories are calculated, for both ground and ro-vibrationally excited initial states of H₂(X?¹Σ⁺_g). Corrections to the zero point energy leakage of the classical calculations are also presented. Calculated reaction cross sections and rate constants are here reported and compared with available literature.     

The valence states of NO+

Spectroscopic constants for the eight lowest electronic states of the NO⁺ ion are tabulated. These constants result from reanalysis of previously reported optical and photoelectron spectra and interpolation from corresponding states of the isoelectronic molecules CO and N₂. Similar spin-orbit perturbations of the A¹Π states of NO⁺ and CO are compared. An interpretation is given of previously reported emission from a beam of long-lived states of NO⁺. The intensities of ionizing transitions from NO X²Π (v = 0) observed in photoelectron spectra are compared with calculated Franck-Condon factors.