Selective non-radiative transitions at excited states of the self-trapped exciton in alkali halides

Generation of F-H pairs and σ-luminescence induced by excitation of the self-trapped excitons with polarized light causing the 1s→ 2p transitions has been measured. The results were analyzed based on the assumption that the non-radiative transitions that follow photoexcitation depend only on the state reached by the excitation, irrespective of the photon energy of the excitation. The absence of the dependence on exciting photon energy of the effective yield of removal from the triplet manifold after excitation to each substate obtained from the analysis proves that the above assumption is valid. The relative non-radiative transition probabilities between the 2p substates and from the 2p-substates to the lowest triplet state, the F-H pair, the σ-luminescent state and the ground state were obtained. It is shown that the de-excitation channels from each substate are substantially different from each other. The following transitions are found to have high probabilities: from the B_1g state to the F-H pairs in KCl and KBr, from theA_g state to the σ-luminescent state and the lowest triplet state in KBr and to the lowest triplet state in KCl and from the B_2g state to the B_1g state in KCl and KBr, where A_g, B_1g and B_2g denote the states with the electron excited to the σ_u orbital, the π_u orbital lying in the (100) plane in which the (halogen)₂^?-molecular ion is situated and the other π_u orbital, respectively. The mechanisms of these non-radiative transitions were discussed.     

Electronic structure of the self-trapped exciton in rare gas solids

The Rydberg-like series of the self-trapped exciton R₂¹ in rare gas solids (Ar, Kr and Xe) are obtained by solving the effective mass equation which incorporates different corrections, including the central cell correction. The results are in good agreement with the recent transient optical absorption data in which the electron is excited into higher excited states. The origin of the luminescence bands is interpreted by analogy with a similar structure of the self-trapped excitons in alkali halides.     

Self-trapped exciton in alkali fluorides: ODMR study

The optical detection technique is used to observe magnetic resonance in the triplet state ³B_1u of the self-trapped exciton in LiF, NaF, KF. The strong anisotropy of the hyperfine interaction in the x?y plane is related to the more localized character of the electronic wavefunction. The magnetic dipolar contribution to the fine structure can be described by a Mollwo-Ivey type law in alkali fluorides and chlorides.     

Doppler-free two-photon absorption spectroscopy of trans-glyoxal under magnetic fields up to 6T

In order to measure the Doppler-free two-photon absorption (DFTPA) spectrum in the presence of a strong magnetic field, a sample cell placed in an optical resonator was installed at the centre of the bore of a superconducting magnet capable of generating a magnetic field of up to 6T. Changes in spectra of the A ¹A_u ← X ¹A_g transition of trans-glyoxal were measured as a function of magnetic field strength. Level crossings induced by Zeeman energy shifts were observed. The perturbing level, which shows hyperfine splitting, was identified as the ³A_u(nπ?) state, because the hyperfine splitting is small in the ³B_u(^ππ?) state and large in the ³A_u(nπ?) state. The perturbation between the A ¹A_u(nπ?) and ³A_u(nπ?) states was shown to take place by either vibronic interaction or Zeeman interaction between the ³A_u(nπ?) state and the ³B_u(ππ?) component mixed to the A ¹A_u(nπ?) state by spin-orbit interaction. The magnetic moment of the A ¹A_u state was determined to be approximately 0.0028μ_B, and the magnitude of the mixing coefficients 〈1 ³B_u|H _so|1 ¹A_u〉/[E(1 ¹A_u) ? E(1 ³B_u)] was evaluated to be 0.026.     

Conversion ratio to F-H center pairs from self-trapped excitons in alkali chloride crystals

Abstract

The time delayed double excitation spectroscopy has been utilized to determine the conversion ratio to F-H center pairs from self-trapped excitons(STE_L) at the lowest state (1s[sgrave]_g;a_1g). The final conversion ratios, η_F/(η_F+η_X), were 0.86, 0.49 and 0.20 for NaCl, KCl and RbCl at 14K, respectively. The conversion efficiency (η =η_F+η_X) from STE_L to F-H center pairs(η_F) and to unknown states(η_X) were 0.25, 0.90 and 0.76 for the hole excitation to π_g, while 0.03, 0.01 and 0.01 for the electron excitation to b_1u, b_2u or b_3u, in NaCl, KCl and RbCl, respectively.     

High-resolution Fourier spectrometry of 14N2 infrared emission spectrum: Extensive analysis of the B3Πg-A3Σu+ system

The B³Π_g-A³Σ_u⁺ system of N₂ excited in a microwave discharge was recorded between 3 000 and 18 000 cm^?1 with a high-resolution Fourier spectrometer. There are no observed irregularities in the levels of the A³Σ_u⁺ and B³Π_g states at least for the values of v and J considered here, except the predissociation in the B³Π_g state for v = 12 and J higher than 33. This predissociation will be checked with more complete data in another article. Thirty three bands of the first positive system with 0 ≤ v′ ≤ 12 and 0 ≤ v″ ≤ 8 are analyzed. The molecular parameters of the B³Π_g and A³Σ_u⁺ are obtained by a complete fitting procedure. Derived values of equilibrium constants are deduced; RKR potential energy curves for the two states are constructed, and the Franck-Condon factors calculated for the A-B system.     

Stress-optical studies of VI B transition metal dichalcogenides

The effect of a uniaxial stress on the excitonic optical spectra are studied for MoS₂, WS₂, MoSe₂ and WSe₂. Stress dichroism appears in the A′, B′ excitons in diselenides, while it is absent in the A, B excitons in the four compounds. The A′, B′ excitons shift oppositely to the A, B excitons, indicating that A, B and A′, B′ are not pair excitons split by interlayer interaction.     

Doppler-free high resolution spectroscopy of carbon disulphide and the effects of a magnetic field

A single-mode autoscan laser spectrometer operating in the ultraviolet in combination with a collimated molecular beam was used to measure high resolution fluorescence excitation spectra of the CS₂ V ¹B₂ ← X ¹Σ⁺ _g transition under collision-free conditions, and the effects of a magnetic field were measured. Rotational and vibrational levels were fully resolved, and Zeeman splittings were observed in many of the perturbed lines. The Zeeman interaction was observed to induce new perturbation, which induces new transitions, level splitting, and energy shift. When the magnetic field strength was changed, the magnitude of the interaction, which was observed in the absence of a magnetic field, changed dramatically depending on the energy shifts of the Zeeman components. It is shown that the V ¹B₂(¹Δ_u) state is mixed with the B₂(³A₂) component by first-order spin-orbit interaction, and through the mixed component, the Zeeman interaction between the V ¹B₂(¹Δ_u) and ³A₂(³Δ_u) states is induced. Large Zeeman splittings were observed for most of the background lines of weak intensity, and this demonstrates that the background levels are levels of the ³A₂(³Δ_u) state. The fluorescence decays of single Zeeman components were observed to be single exponential. The lifetimes of the perturbing ³A₂(³Δ_u) levels were determined by deperturbation analysis. Triplet-triplet ³A₂(³Δ_u) → ³B₂(³Σ⁺ _u) emission was confirmed. It was demonstrated that the quenching of the V ¹B₂ → X ¹Σ⁺ _g fluorescence by a magnetic field was caused by mixing of the ³A₂ state with the V ¹B₂ state and the resulting increase of triplet-triplet emission. In a time-dependent picture, the intersystem crossing from the ¹B₂(¹Δ_u) and ³A₂(³Δ_u) states is enhanced by the magnetic field.     

The Raman Spectrum and Full Vibrational Assignment of Ethylenediamne Dihydrochloride

A full vibrational analysis was recently made for the H³N⁺CH₂CH₂N⁺H₃ ion, on the basis of infrared measurements, and a partial vibrational assignment proposed¹. The observed fundamentals were interpreted In terms of a C_2h, symmetry for the ion. There are thirty-six fundamentals (r - lla_g + 8A_u + 7B_g + 10B_u; A_g and B_g Raman-active only; A_u and B_u infrared-active only). In addition to the eighteen infrared-active vibrations, a number of bands was observed which were assigned as formally forbidden Raman-active modes, excited by strong hydrogen bonding causing departure from the exact site symmetry of the species.     

用能量自洽法研究碱金属双原子分子的势能曲线

用能量自洽法(ECM)研究了碱金属双原子分子一些电子激发态的势能曲线：Na₂ 分子的2¹Π_g,4³Π_g和b³Π< sub>u电子激发态,K₂分子的a³Σ^＋_{u,2¹Πg,B¹Πu和A^{关键词： 能量自洽 双原子分子 势能 碱金属}}     

Comparative study of the semiempirical three-parameter potential energy functions for diatomic molecules

A comparative study is made of four three-parameter semiempirical potential energy functions for 32 electronic states of diatomic molecules and their ions:n ₂:X¹gS _g ⁺ ,B ³π_g,A ³ gS_u,C ³ _u,B′ ³ gS_u.a ¹ π_g, a′gS _u ^? ,Ω ¹δ_u N ₂ ⁺ :X ² gS _g ^gS +A ² π,C ² gS _u ⁺ ,B ² gS _u ⁺ CO:X¹gS⁺,a ³ π, a′³ gS_u,e ³ gS^?,d ³gD₁,A ¹π CO⁺:X²gS⁺,A ² π,B ²gS⁺ O₂:X³gS _g ^? ,B ³ gS_u,c ¹ gS _u ^? ,b ¹gS _g ^s ,a ¹ δ_g,c ³ δ_u O ₂ ⁺ :X ²π_g,A ² π_g, a¹ π_g,b ⁴ gS _g ^? A program for numerically integrating the radial Schrödinger equation by the Cooley method is worked out. Certain additional units are introduced to conserve computer time. The resulting vibrational levels are compared with the experimental levels for all the electronic states studied. It is concluded on the basis of this analysis that it is not possible to describe equally well all the electronic states of various molecules on the basis of any single three-parameter potential function. A method for choosing a potential function for describing some particular electronic state of a diatomic molecule is proposed.     

The triplet spectrum of tetramethyl-1,3-cyclobutanedione

The low-temperature single-crystal spectrum of TMCBD has revealed a low-lying triplet state at 25 718 cm^-1 (72·5 kcal/mol). The observed band is ascribed to a ³ A_u (³ A ₂) ← ¹ A_g nπ* transition on the basis of its small singlet-triplet splitting, its polarization behaviour, and its vibrational structure. The ³ A_u state is first-order spin-orbit coupled to either or both of the ¹ B _2u or ¹ B _3u states. No evidence for two or more nπ* transitions was found. Several multi-membered progressions in the carbonyl wagging mode indicate the presence of a distorted excited state, in which the carbonyl carbons attain a pyramidal conformation. Analysis of the site symmetry shows that TMCBD is distorted to a boat-shaped C _2v structure in its triplet nπ* state.     

Ab initio calculation of transition dipole moments for transitions between valence states in oxygen molecules

Results of ab initio calculations of potential-energy curves for 20 singlet and 20 triplet valence states of oxygen with configuration interaction taken into account in the 6-31G basis are presented. Transition dipole moments of triplet-triplet (1³Π_g ← B ³Σ _u ^? , 1³Π_g ← A ³Σ _u ⁺ , 1³Π_g ← A′ ³Δ_u, B ³Σ _u ^? ← X ³Σ _g ^? , 2³Π_u ← 1³Π _g, 2³Σ _g ^? ← B ³Σ _u ^? , 1³Π_u ← X ³Σ _g ^? , 2³Π_u ← X ³Σ _g ^? , 2³Π _g ← A′³Δ_u, 3³Π_g ← A′ ³Δ _u, 2³Δ_u ← 2³Π_g, 3³Π_g ← B ³Σ _u ^? , and 2³Π_g ← A ³Σ _u ⁺ ) and singlet-singlet (2¹Σ _g ⁺ ← 2¹Π_u, 2¹Π_u ← 1¹Π ^g, ¹Π_u ← 2¹Δ_g, 1¹Π_g ← c ¹Σ _u ^? , ¹Π_u ← b ¹Σ _g ⁺ , 1¹Δ _u ← a ¹Δ_g, 2¹Π_u ← a ¹Δ_g, 2¹Δ_g ← 1¹Δ_u, ¹Π _u ← a ¹Δ _g, 1¹Π_u ← b ¹Σ _g ⁺ , 2¹Π_g ← 1¹Π_u, 2¹Π _g ← c ¹Σ _u ^? , 1¹Δ _u ← 1¹Π _g, f′Σ _u ⁺ ← b ¹Σ _g ⁺ , 2¹Σ _g ⁺ ← f ′¹Σ _u ⁺ , 3¹Π_g ← 1¹Δ_u) radiative transitions are calculated as functions of internuclear separation. The possibility of observing these transitions under experimental conditions is discussed.     

Fluorescence of Na2 and K2 excited by a gold vapor laser

The gold vapor laser has been used to irradiate the alkali dimers Li₂, Na₂, K₂, and Rb₂. Significant fluorescence was found only from Na₂ and K₂. Six fluorescent series in the A¹Σ_u⁺-X¹Σ_g⁺ system of Na₂ and three in the B¹Π_u-X¹Σ_g⁺ system of K₂ were assigned, respectively. New spectroscopic constants for the X¹Σ_g⁺ state of ³⁹K₂ are derived, and new RKR potential energy curves for the X¹Σ_g⁺ and B¹Π_u states of ³⁹K₂ are given.     

Probable location of a 1E2g state of the benzene molecule

Photoexcitation spectra of benzene in rare gas matrices show a previously unreported transition near 46000 cm^?1. The observed bands are not explicable in terms of site splittings, impurity states, aggregation effects, intermediate radius states of the matrix, triplet states, excimer states, exciplex states or $\text{σ-π}{}^1$ transitions. The vibronic spacings in these spectra could be those expected for a ¹E_2g ← ¹A_1g transition and on this and other evidence we argue that the ordering of origins of the first four spin allowed intravalence states of benzene is ¹B_2u (38086 cm^?1), ¹E_2g (near 46400 cm^?1), ¹B_1u (48450 cm^?1) and ¹E_1u (55430 cm^?1). Our data also show that the transition ¹B_1u ← ¹A_1g accounts for most of the intensity of the 210 nm absorption band system. Our ordering of the spin allowed states permits interpretation of experimental data of others, confirms certain semi-empirical and ab initio SCF MO CI calculations in which account is taken of higher excitations and illustrates the necessity of including such higher excitations. The intensity of the ¹E_2g ← ¹A_1g transition is at least an order of magnitude less than previously calculated indicative of the difficulty of choosing suitable wavefunctions for the ¹E_2g state and of calculating “forbidden” transition probabilities.     

High-resolution Fourier spectrometry of 15N2 infrared emission spectrum: Extensive analysis of the B3Πg-A3Σu+ system

The emission spectrum of the B³Π_g-A³Σ_u⁺ system of the ¹⁵N₂ molecule was recorded between 3500 and 12 500 cm⁻¹ with a high-resolution Fourier spectrometer. Twelve bands with 0 < v′ < 5 and 0 < v″ < 9 are analyzed. The molecular parameters of the B³Π_g and A³Σ_u⁺ states are obtained by a complete fitting procedure. Derived values of equilibrium constants are deduced; the Franck-Condon factors are calculated for the B-A system of ¹⁵N₂.     

Enhanced optical nonlinearity based on silicon ring

The photoelectron spectrum of ethylene is studied using coupled cluster methods, including an existing ambiguity in what are reported to be its experimental vertical ionization potentals. Two complementary methods are used for generating the ionization potentials: δE CCSD(T) and IP-EOM-CCSD. The adiabatic IP of the neutral molecule in the ground state is well known and widely accepted to be 10.5122eV. The basis set extrapolated adiabatic IPS with zero-point corrections are 10.46 eV and 10.56 eV, respectively, but a vibronic coupling between the ground state cation and its first excited state can reduce these values by ～0.03 eV. From an exponential basis set extrapolation the vertical ionization potentials are predicted to be 10.8 eV (B_3u, 13.2eV (B_3g 15.0eV (A_g), 16.4eV (B_2u), and 19.6eV (B_1u) ±0.1 eV.     

Applications of photoelectron spectroscopy to molecular propertles: XVIII. The vertlcal ionization potentials of diphosphene as calculated by perturbation corrections to koopmans' theorem

The vertlcal ionization potentials (VIP's) of dimethyl diphosphene have been computed using perturbation corrections to Koopmans' theorem. These corrections allow an estimate of the effects of polarization and correlation, and show for this molecule an important contribution of the specific correlation of the ion for the ²A_g and ²B_u states. The results predict for the first three VIP's the ordering ²A_g, ²A_u, ²B_u, in agreement with our previous assignment.