Studies on the full vibrational energy spectra for some electronic states of diatomic molecular ions XY+

The first accurate studies on the vibrational spectroscopic constants and the corresponding full vibrational energy spectra of some electronic states of diatomic molecular ions XY⁺ were performed using algebraic method(AM). The AM is applied on the X¹Σ⁺ state of BeH⁺, the X²Σ⁺ state of CO⁺, the X²Π_g state of F ₂ ⁺ , the A²Π_u state of O ₂ ⁺ and the X²Σ _g ⁺ state of Li ₂ ⁺ . The results show that AM can generate accurate vibrational spectroscopic constants as well as accurate full vibrational energy spectra by using some accurate experimental vibrational energies, and that the AM vibrational energies are better than other theoretical data. __________ Translated from Chinese Journal of Atomic and Molecular Physics, 2005, 22 (4) (in Chinese)     

Photoelectron spectra of halides

High resolution photoelectron spectra, obtained with He I (584 Å) resonance radiation, are reported for ClF, ClF₃, BrF₃ and BrF (partial spectrum). In some cases Ne I (736–744 Å) radiation has also been used. Spinorbit and vibrational fine structure is resolved for the ground ²II states of ClF⁺ and BrF⁺; values obtained for ClF⁺ and ζ = 630 cm^-1, v′ = 870 cm^-1, and for BrF⁺ ζ = 2600 cm^-1, v′ = 750 cm^-1. From the vibrational envelope of the X ²∏ states, a bond length change of δr _e (-)0·10 Å for ClF⁺ and BrF⁺ is estimated. Ab initio SCF-MO calculations for ClF and ClF₃ are used to aid in the interpretation of the spectra via Koopmans' theorem. A considerable amount of charge delocalization in the trifluorides is inferred from the photoelectron spectra, and this is borne out by the calculations.     

WnNim(n+m=8)团簇的极性和光谱性质的理论研究

采用密度泛函理论(DFT)中的B3LYP方法,在LANL2DZ基组水平上对WnNim(n+m=8)团簇的各种可能构型进行了几何参数全优化,得到了它们的基态构型;并对基态构型的偶极距、极化率、红外光谱和拉曼光谱性质进行了分析,结果表明:团簇WnNim(n+m=8)都具有极性,富W团簇非线性光学效应强,容易被外加场极化;振动频率主要分布在0-350 cm-1范围内,团簇W4Ni4因其振动方式的特殊性,红外光谱和拉曼光谱在频率421.971 cm-1处,都有明显强峰;团簇W5Ni3因其结构的高对称性在振动光谱中出现多处共振现象.     

Analysis of the Δv = 0 sequence of the β(cΦ - aΔ) system of the TiO molecule

Rotational analyses have been performed on the emission spectra of the 0-0, 1-1, 2-2, and 3-3 bands of the β system (c¹Φ - a¹Δ) of the TiO molecule, excited in a microwave discharge through a mixture of helium, oxygen and TiCl₄ vapor. Rotational constants were obtained for all the bands from which the following equilibrium constants were derived. Be^‘=0.52301±0.00008 cm⁻, αe^‘=0.00313±0.0006 cm⁻, re⁻=1.6391±0.0001 AHigher order constants, D_v and H_v, were calculated for the various vibrational levels.     

Vibrational wave packet dynamics in the silver tetramer probed by NeNePo femtosecond pump-probe spectroscopy

We present results on the ultrafast dynamics of mass-selected neutral Ag₄ clusters using NeNePo (negative ion - neutral - positive ion) femtosecond pump-probe spectroscopy. One-color pump-probe spectra of the Ag₄ ^-/Ag₄/Ag₄ ⁺ system measured at 385 nm and an internal cluster temperature of 20 K display a complex beat structure over more than 60 ps. The oscillatory structure is attributed to vibrational wave packet dynamics in an excited “dark" state of neutral Ag₄. A dominant 740 fs wave packet period as well as wave packet dephasing and rephasing are observed in the spectra. Fourier analysis of the spectra yields a group of frequencies centered around 45 cm^-1 and an anharmonicity χ _e2νχ _eχ _e of 2.65 cm^-1 for the active vibrational mode. Received 30 November 2000     

Resonances and chaos in the collinear collision system (He,H 2 + ) and its isotopic variants

The collinear atom-diatom collision system provides one of the simplest instances of chaotic or irregular scattering. Classically, irregular scattering is manifest in the sensitive dependence of post-collision variables on initial conditions, and quantally, in the appearance of a dense spectrum of dynamical resonances. We examine the influence of kinematic factors on such dynamical resonances in collinear (He, H ₂ ⁺ ) collisions by computing the transition state spectra for collinear (He, HD⁺) and (He, DH⁺) collisions using the time-dependent quantum mechanical approach. The nearest neighbor spacing distributionP(s) and the spectral rigidity Δ₃(L) for these resonances suggest that the dynamics is predominantlyirregular for collinear (He, HD⁺) and predominantlyregular for collinear (He, DH⁺). These findings are reinforced by a significantly larger “correlation hole” in ensemble averaged survival probability ≪P(t)≫ values for collinear (He, HD⁺) than for collinear (He,DH⁺). In addition we have also examined measures of classical chaos through the dependence of the final vibrational action,n _f, on the initial vibrational phaseφ _i of the diatom, and Poincaré surfaces-of-section. They show that (He, HD⁺) collisions are partly chaotic over the entire energy range (0–2.78 eV) while (He, DH⁺) collisions, in contrast, are highly regular at collision energies below the classical threshold for reaction. Above the threshold, the scattering remains regular for initial vibrational statesv=0 and 1 of DH⁺.     

Generation of CdS clusters using laser ablation: the role of wavelength and fluence

The formation of cationic clusters in the laser ablation of CdS targets has been investigated as a function of wavelength and fluence by mass spectrometric analysis of the plume. Ablation was carried out at the laser wavelengths of 1064, 532, 355, and 266 nm in order to scan the interaction regimes below and above the energy band gap of the material. In all cases, the mass spectra showed stoichiometric Cd _n S _n ⁺ and nonstoichiometric Cd _n S _n−1⁺, Cd _n S _n+1⁺, and Cd _n S _n+2⁺ clusters up to 4900 amu. Cluster size distributions were well represented by a log-normal function, although larger relative abundance for clusters with n=13, 16, 19, 34 was observed (magic numbers). The laser threshold fluence for cluster observation was strongly dependent on wavelength, ranging from around 16 mJ/cm² at 266 nm to more than 300 mJ/cm² at 532 and 1064 nm. According to the behavior of the detected species as a function of fluence, two distinct families were identified: the “light” family containing S₂⁺ and Cd⁺ and the “heavy” clusterized family grouping Cd₂⁺ and Cd _n S _m ⁺. In terms of fluence, it has been determined that the best ratio for clusterization is achieved close to the threshold of appearance of clusters at all wavelengths. At 1064, 532, and 355 nm, the production of “heavy” cations as a function of fluence showed a maximum, indicating the participation of competitive effects, whereas saturation is observed at 266 nm. In terms of relative production, the contribution of the “heavy” family to the total cation signal was significantly lower for 266 nm than for the longer wavelengths. Irradiation at 355 nm in the fluence region of 200 mJ/cm² has been identified as the optimum for the generation of large clusters in CdS.     

Static and dynamic structure factors with account of the ion structure for high-temperature alkali and alkaline earth plasmas*

The electron-electron, electron-ion, ion-ion and charge-charge static structure factors are calculated for alkali (at T = 30 000 K, 60 000 K, n _e = 0.7 × 10²¹ ÷ 1.1 × 10²² cm^-3) and Be²⁺ (at T = 20 eV, n _e = 2.5 × 10²³ cm^-3) plasmas using the method described by Gregori et al. The dynamic structure factors for alkali plasmas are calculated at T = 30 000 K, n _e = 1.74 × 10²⁰, 1.11 × 10²² cm^-3 using the method of moments developed by Adamjan et al. In both methods the screened Hellmann-Gurskii-Krasko potential, obtained on the basis of Bogolyubov's method, has been used taking into account not only the quantum-mechanical effects but also the repulsion due to the Pauli exclusion principle. The repulsive part of the Hellmann-Gurskii-Krasko (HGK) potential reflects important features of the ion structure. Our results on the static structure factors for Be²⁺ plasma deviate from the data obtained by Gregori et al., while our dynamic structure factors are in a reasonable agreement with those of Adamyan et al.: at higher values of k and with increasing k the curves damp down while at lower values of k, and especially at higher electron coupling, we observe sharp peaks also reported in the mentioned work. For lower electron coupling the dynamic structure factors of Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ do not differ while at higher electron coupling these curves split. As the number of shell electrons increases from Li⁺ to Cs⁺ the curves shift in the direction of low absolute value of ω and their heights diminish. We conclude that the short range forces, which we take into account by means of the HGK model potential, which deviates from the Coulomb and Deutsch ones, influence the static and dynamic structure factors significantly.     

High-resolution F T spectrum of A2Πr-X2Σ+ band system of MgCl

The emission spectrum of the A ² Π _r -X ² Σ ⁺ band system of MgCl molecule (360–380 nm) has been recorded on BOMEM DA8 Fourier transform spectrometer at an apodized resolution of 0.035 cm⁻¹. The spectra have been excited under flowing conditions in a demountable stainless steel hollow cathode lamp (400 V, 250 mA) containing anhydrous MgCl₂ and Ar. The resulting spectra are very intense and the 0-0, 1-1, 1-0 bands of A ² Π _1/2-X ² Σ ⁺ sub-transition and the 0-0 band of A ² Π _3/2-X ² Σ ⁺ sub-transition have been rotationally analyzed. Improved molecular constants have been derived using a least-squares fit program in which optical data of earlier analyzed 0-1 and 0-2 bands (A ² Π _1/2-X ² Σ ⁺) was also included. The Λ-doubling constants in the v′ = 0, 1 levels of the A ² Π _1/2 sub-state are as expected, i.e. p ₁ > p ₀, where as it is found that the spin-doubling constants of the v″ = 0, 1 and 2 levels of the ground state X ² Σ ⁺, decrease with the increase in v, i.e. γ ₀ > γ ₁ > γ ₂. This is indicative of the presence of some nearby state, influencing the spin-doubling.     

Optical absorption behavior of Tl<Superscript>+</Superscript> DOPED Rb(Br<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>I<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>) system

The optical absorption behavior of Tl⁺ doped Rb(Br_1–x I _x ) mixed crystals (with x = 0.00, 0.05, and 0.10) grown under vacuum by slow cooling from the melt has been studied. Absorption spectra of the mixed crystals recorded at room temperature showed that the characteristic A-absorption band of Tl⁺ ions in the Rb(Br_1–x I _x ) system (0.1 mol. %) with x = 0.00 (i.e., RbBr:Tl⁺) broadened with the iodine content towards the low energy side. Changes in the absorption spectra of the mixed crystals are due to creation of some complex centers involving Tl⁺, Br^–, and I^- ions with energy levels inside the band gap while forming the mixed crystal. The absorption spectra of gamma-irradiated mixed crystals showed the F-band, which shifted towards the low energy side due to the existence of iodine ions in the mixed crystals.     

Application of CI expansion techniques to the computation of two-photon absorptivities

Summary We show how conventional linear expansion techniques for both electronic and vibrational wave functions can be used for the computation of matrix elements governing the two-photon absorption probability in molecules. In particular, the²Σ⁺ A←²∏X transition matrix elements of OH and the¹Σ _g ⁺ E,F←¹Σ _g ⁺ X of H₂are computed using 1) the sum over states in the Born-Oppenheimer approximation with inclusion of vibrational wave functions, 2) solution of perturbation theory equations by expansion in the CI basis at fixed nuclei, followed by a kind of vibrational averaging. The results are compared with experiment and discussed. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

High-resolution mass spectra of the residual gas in a metallic vacuum system

The mass spectra of the residual gas in a metallic vacuum chamber of capacity 3 l are studied with an MI-9303 high-resolution magnetic resonance mass spectrometer in the mass range 1–140 u. The experiments are carried out under four evacuation conditions in the pressure range P = 10⁻⁸–10⁻¹⁰ Torr, and almost all the mass peaks forming multiplets are resolved. It is shown that the multiplets with mass numbers M≤80 have, as a rule, a multicomponent structure and hydrogen is the basic component responsible for the total pressure in the chamber irrespective of evacuation conditions. Next in order of intensity in the mass spectra are, CH ₄ ⁺ , H²O⁺, CO⁺, and CO ₂ ⁺ peaks. Other lines in the residual gas spectra are largely due to various C-, H-, N-, and O-based compounds. In addition, the background mass spectrum involves Cl-and F-based compounds and noble gas isotopes. The multiplets with M > 80 often degenerate into a single hydrocarbon line.     

Interaction of gold and silver cluster cations with CH<Subscript>3</Subscript>Br: thermal and photoinduced reaction pathways

The reactions of free, size selected Au _n ⁺ (n = 1–3, 5, 7) and Ag₃ ⁺ clusters with CH₃Br as well as the photodissociation of the resulting complexes at 266 nm were studied in a radio frequency ion trap under multiple collision conditions. CH₃Br was found to interact more strongly with the gold clusters than with the silver clusters. All investigated metal clusters exhibited characteristic size dependent adsorbate coverages. Furthermore, the successive loss of methyl radicals was identified as a major thermal reaction channel of the adsorbed CH₃Br molecules. Photodissociation experiments were performed with the product complexes of the trimer clusters and revealed the strongly preferred light-induced fragmentation of Au₃Br₃ ⁺ and Ag₃Br₃ ⁺, respectively, over any other thermal reaction products. However, whereas in the case of the gold cluster complexes the bare Au₃ ⁺ was exclusively re-formed through laser irradiation, considerable photoinduced metal cluster fragmentation occurred in the case of Ag₃Br₃ ⁺.     

Study of spatial characteristics of the incomplete surface discharge in atmospheric-pressure air

Spectra of plasma of the incomplete surface discharge in atmospheric-pressure air were measured. Bands of the systems 2⁺, 1⁺, and 1⁻ of nitrogen were identified. It was shown that periodic excitation at the C ³Π _u nitrogen level results in local equilibrium characterized by a vibrational temperature of 2250 K. For the 1⁺ band system of nitrogen, the structure of rotational transitions was resolved; it was found that the distribution in the 1⁺ band system is significantly nonequilibrium due to the A ³Σ _u ⁺ level metastability. Transverse and longitudinal sections of the plasma band were scanned. It was found that the transverse distribution of the emission intensity has a maximum at a distance of 1 mm from the electrode edge followed by an exponential decay. The plasma band width was ∼5 mm. The longitudinal discharge structure consisted of a system of microchannels (with a characteristic diameter of 0.4 mm) with diffuse overlapping. The average channel density was 10–15 cm⁻¹. It was shown that the spatial distribution of incomplete discharge plasma is characterized by high stability against wide-range variations of discharge electrical characteristics. For example, as the excitation voltage varies within 2–6 kV, the plasma band width changed by no more than 1 mm, and the vibrational temperature varied within 10–12%.     

Rotational and vibrational relaxation of the NO3 - ion in molten binary systems (M,Ag)NO3 (M = Li,Na and K) by Raman spectroscopy

Polarized and depolarized Raman scattering spectra for the totally symmetric stretching υ₁ mode of nitrate ions (D_3h symmetry) in the molten binary systems (M1,Ag)NO₃(M1= Li, Na, and K) have been measured. Vibrational and rotational autocorrelation³ functions, C_v(t) and C_r(t), respectively, have been evaluated from Fourier transformation of the spectra. The shifts in the peak frequencies are deeply correlated with the polarizability of silver in these mixtures. The vibrational relaxation rate increases with increasing mole fraction of silver nitrate in (K,Ag)NO₃, but does not vary so much in (Li,Ag)NO₃ and (Na,Ag)NO₃. The vibrational relaxation time negatively deviates from additivity on the order of (Na,Ag)NO₃&lt; (Li,Ag)NO₃&lt; (K,Ag)NO₃. In the systems (Na,Ag)NO₃ and (K,Ag)NO₃ rotational relaxation time becomes slower with increasing concentration of AgNO₃. The Ag⁺ coordinating to several nitrate ions in these mixtures appreciably restricts the rotational motion of the nitrate ions. On the other hand, rotational motion becomes easier in the mixture system (Li,Ag)NO₃ mainly because the different preferential sites of the two cations coordinating to an NO₃ ^-ion, and partly because the exchange rates of these cations around the NO_-3 ^-ion are high.     

分子部分电子态的高阶振动能级和离解能的精确研究

鉴于K₂分子电子态的振动能谱和分子离解能D_e在实际研究和应用中的重要性,应用Sun,Ren等人提出的基于微扰理论的代数方法(AM)和基于AM的代数能量方法(AEM)研究了K₂分子的X¹Σ⁺_g,a³Σ⁺_u,0^-_g,B¹Π_{u< 关键词： 2}分子')" href="#">K₂分子 代数方法 高阶振动能级 离解能     

Theoretical study of the electronic structure of LiNa and LiNa<Superscript>+</Superscript> molecules

Adiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels of the lowest electronic states of the alkali dimer LiNa molecule dissociating into Na (3s, 3p, 4s, 3d, and 4p) + Li (2s, 2p, 3s, and 3p) in ^1,3Σ, ^1,3Π, and ^1,3Δ symmetries are presented. Adiabatic results are also reported for ²Σ, ²Π, and ²Δ electronic states of the molecular ion LiNa⁺ dissociating into Li (2s, 2p, 3s, and 3p) + Na⁺ and Li⁺  + Na(3s, 3p, 4s, 3d, and 4p). We use an ab initio approach involving a non-empirical pseudopotential for the Li (1s²) and Na (1s²2s²2p⁶) cores and core valence correlation correction. A very good agreement is obtained for some lowest states of the LiNa and LiNa⁺ molecules for spectroscopic constants with the available theoretical works. The existence of numerous avoided crossings between electronic states of ²Σ and ²Π symmetries is related to the charge transfer process between the two ionic systems Li⁺Na and LiNa⁺.     

Time-dependent analysis of tunneling effect in the formation of ultracold molecules via photoassociation of laser-cooled atoms

The paper contains a time-dependent investigation of the tunneling effect observed in the photoassociation spectrum of Cs₂ and attributed to the 0_g ^-(6s, 6p _3/2) double well. When by photoassociation of two cold cesium atoms a vibrational level of the outer well is populated, tunneling is an efficient mechanism for transferring the population to the inner well (R < 15a ₀), where spontaneous emission may lead to formation of cold molecules in low vibrational levels of the a ³Σ⁺ _u(6s, 6s) electronic state. This tunneling effect is analyzed by wavepackets propagation, first considering the double well potential alone, and following a packet made by a superposition of states initially located at large distances. Characteristic times for the vibration dynamics, corresponding to a beating phenomenon between the two wells, to partial “revival” at large distances, and to maxima in the population localized in the inner well are reported and discussed. Second, we simulate the two-channels a ³Σ⁺ _u(6s, 6s)↦0_g ^-(6s, 6p _3/2) photoassociation at detunings around 2.9 cm^-1: the inner well can be populated either by the excitation of a vibrational level of the external well (resonant excitation), or by tuning the photoassociation laser at the energy of the inner well level which displays tunneling (“off-resonance excitation”). In the first case the photoassociation is efficient, while the tunneling probability is small; in the second, the tunneling probability is large, so that despite the poor efficiency of the photoassociation process, more population can be transferred to the inner well. This second choice is shown to be very sensitive to the laser intensity, which could be used to control the population of the inner well and hence the formation of ultracold molecules in low vibrational levels. Received 19 April 2002 Published online 1st October 2002 RID="a" ID="a"e-mail: francoise.masnou@lac.u-psud.fr     

Calculation of the spectroscopic constants for the electronic states A1Σ u+ , B1Πu, C1Πu, D1Σ u+ , and E1Σ u+ of the cesium dimer

The vibrational, rotational, and centrifugal distortion constants have been calculated for the electronic states A ¹Σ _u ⁺ , B ¹Π_u, C ¹Π_u, D ¹Σ _u ⁺ , and E ¹Σ _u ⁺ of the Cs₂ molecule. The calculation was performed on the basis of the semiempirical potential energy curves constructed in this paper. The calculated spectroscopic constants are compared with the experimental data. Original Russian Text ? A.D. Smirnov, 2007, published in Optika i Spektroskopiya, 2007, Vol. 102, No. 1, pp. 23–27.     

Profiling the binding motif between Be and Mg in the ground state via a single-reference coupled cluster method

We present a study on the performance of our iterative triples correction for the coupled cluster singles and doubles excitations (CCSDT-1a+d) method for computation of potential energy surface (PES), spectroscopic constants, and vibrational spectrum for the ground state (X¹Σ⁺) BeMg, where the ostensible inadequacy of the CCSD and CCSD(T) methods is quite expected. We compare our results with those obtained using state-of-the-art multireference configuration interaction (MRCI) investigations reported earlier by Kerkines and Nicolaides. Our estimated dissociation energy (417.37 cm^?1), equilibrium distance (3.285 Å), and vibrational frequency (82.32 cm^?1) are in good agreement with recent results of advanced MRCI calculations for X¹Σ⁺ BeMg PES, which exhibits a shallow well of 469.4 cm^?1 with a minimum at 3.241 Å and a harmonic vibrational frequency of 85.7 cm^?1. Very weakly bound nature of X¹Σ⁺ BeMg is clearly reflected from these values. In accord with MRCI studies, a comparison of BeMg with iso-valence weakly bound ground-state species, Be₂ and Mg₂, suggests that its characteristics do not exhibit any resemblance to Be₂ rather, it shows a close kinship to Mg₂. The agreement of our derived vibrational levels with those obtained via the high-level MRCI calculations is very encouraging reflecting the potential of the suitably modified single-reference coupled cluster (SRCC) method, CCSDT-1a+d as a tool for the study of multireference van der Waals systems.