Higher Excited Electronic States Research Articles

Energy Level Structure and Multiple 4f125d1 Emission Bands for Tm2+ in Halide Perovskites: Theory and Experiment

Rapid nonradiative relaxation from high-excited electronic states to lower-excited electronic states in luminescent materials leads to radiative transitions only from the lowest excited state. This behavior is observed in most luminescent materials. One notable exception is Tm2+, which is known to show luminescence from up to three 4f125d1 excited states. Here we report a study that explains the deviant behavior of Tm2+. Using ab initio wave function-based embedded-cluster calculations in Tm2+ -doped CsCaBr3 and CsCaCl3, we show that the manifold of 4f125d1 excited states shows various energy gaps for states with parallel potential energy surfaces. This strongly limits nonradiative relaxation, enabling emission from highly excited states in the case of a large energy gap to the next lower state. We also compared calculated and measured absorption and emission spectra and radiative decay times of the emitting states, which show a remarkably good agreement between theory and experiment. Based on the new ins...

Dipole Moment and Electronic Structure Calculations of the Electronic States of the Molecule SiC below 97000cm-1

Beside its importance in the astrophysics, the silicon carbide has a great importance in the industry of semiconductors and ceramics. Because of the absence of theoretical data, extensive ab initio calculations of dipole moment and higher excited electronic state have been done for this molecule. These calculations have been performed by using the Complete Active Space Self Consistent Field (CASSCF) with Multireference Configuration Interaction MRCI+Q (singly and doubly excitation with Davidson corrections). The potential energy and the dipole moment curves for the 47 low-lying singlet, triplet and quintet electronic states in the representation 2s+1Λ(+/-) of the molecule SiC have been calculated. The harmonic frequency we, the internuclear distance Re, the electronic energy with respect to the ground state Te, the rotational constants Be and the permanent dipole moment have been obtained for these electronic states. The comparison between the values of the present work and those available in the literature, for several electronic states, shows a good agreement. In the present work thirteen new electronic states have been investigated here for the first time. These new results may leads to more investigation of new experimental works on this molecule.

Molecular polarizability in quantum defect theory: Non-polar molecules

The Green function in the quantum defect theory provides an exact account for the high-excited and continuum electronic states. We modify it by taking into account the ground and low-excited states using their wavefunctions calculated ab initio. As an application we present simple and efficient semi-analytical method for calculation of dynamic polarizabilities of nonpolar molecules. The method is applied to alkali dimers Li$_{2}$, Na$_{2}$ and Rb$_{2}$. The result of benchmark calculation (H$_{2}$ molecule) are in good agreement with experimental data; the accuracy achieved is comparable with that of ab initio calculations. We also calculate Verdet constants of the above molecules in Becquerel approximation.

Accelerated and Efficient Photochemistry from Higher Excited Electronic States in Fulgide Molecules

The photoinduced electrocyclic ring-opening of a fluorinated indolylfulgide is investigated by stationary and ultrafast spectroscopy in the UV/vis spectral range. Photoreactions, initiated by optical excitation into the S(1) (570 nm) and S(N) (340 nm) absorption band of the closed isomer, lead to considerable differences in reaction dynamics and quantum yields. Transient absorption studies point to different reaction pathways depending on the specific excitation wavelength: excitation into the S(1) state leads to the known reaction behavior with a picosecond decay to the ground state and a small quantum yield of 7% for the photoproduct. The S(N) state shows an unexpected long lifetime of 0.5 ps. The photoreaction starting from the S(N) state leads to a large extent directly to the product ground state and back to the educt ground state. This results in an increased reaction quantum yield of 28%. In contradiction to Kasha's rule, the S(1) state is only populated with an efficiency of 38%. The observed behavior strongly differs from the expected picture with fast relaxation into the S(1) state and a subsequent ring-opening reaction starting from the lowest excited electronic state. Quantum chemical calculations confirm and complement the experimental findings allowing a sound molecular interpretation to be obtained.

The higher excited electronic states and spin–orbit splitting of the valence band in three-dimensional assemblies of close-packed ZnSe and CdSe quantum dots in thin film form

Optical properties of as-deposited and annealed thin films composed of three-dimensional arrays of sphalerite-type ZnSe and CdSe quantum dots (QDs), synthesized by chemical deposition, were investigated. Neglecting the S– D mixing of hole states, the lowest “band to band” transitions in very small nanoclusters and in bulk-like clusters may be assigned as 1 S→1 S and 1 S Δ →1 S, and are split by spin–orbit (SO) splitting energy of the bulk material— Δ. The splitting energy between these transitions was found to be insensitive to QD size variations, which could be explained assuming that 1 S hole states arising from valence band Γ 7 and Γ 8 components do not mix with higher angular momentum states and shift together to higher energies coupled via the isotropic hole mass. This implies significant difference between the SO splitting energies in the two semiconductors. Accounting for S– D mixing of hole states, the observed transitions may be attributed to the fundamental ground state—(1 S 3/2, 1 S e) and the ground state—(1 S 1/2, 1 S e) ones. The observed “splittings” thus do not correspond exactly to SO splitting energy in both semiconductors, but are complex functions of it, as exact position of each hole energy level depends, besides on Δ, also on other material-characteristic parameters.

Kinetic-energy–angle differential distribution of photofragments in multiphoton above-threshold dissociation ofD2+by linearly polarized400−nmintense laser fields: Effects of highly excited electronic states

We have performed a detailed calculation of the double-differential angular\char21{}kinetic-energy distribution of photofragments in above threshold dissociation (ATD) of $\mathrm{D}_{2}{}^{+}$ from initial vibrational-rotational levels ${v}_{i}=4,5$ and ${J}_{i}=0,1$ in an intense linearly polarized laser field of wavelength $400\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and intensity $3\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$. The calculation used a time-independent close-coupling (CC) formalism with eight (ten) electronic states included in the basis-set expansion of the molecular wave function. The molecular electronic states included, apart from the two lowest $1s{\ensuremath{\sigma}}_{g}$ and $2p{\ensuremath{\sigma}}_{u}$ states, were $2p\ensuremath{\pi}_{u}{}^{\ifmmode\pm\else\textpm\fi{}}$, $2s{\ensuremath{\sigma}}_{g}$, $3p{\ensuremath{\sigma}}_{u}$, $3d{\ensuremath{\sigma}}_{g}$, $3d\ensuremath{\pi}_{g}{}^{\ifmmode\pm\else\textpm\fi{}}$, and $4f{\ensuremath{\sigma}}_{u}$. All the higher electronic states dissociate to the atomic state $\mathrm{D}(2\ensuremath{\ell})$. A sufficient number of photon absorption channels, $n=0\char21{}7$, and molecular rotational quantum numbers $J=0\char21{}11$ were taken into account to ensure the convergence of the multiphoton ATD probability. Altogether 198 coupled channels had to be considered in the calculation. The calculations reveal signatures of significant ejection of the photodissociation fragments away from the laser polarization direction due to the inclusion of the higher excited electronic states. The ratio of the photofragments perpendicular to and along the polarization axis shows good quantitative agreement with the experimental result. The angular distributions show considerable structures depending on the relative kinetic energies of the photofragments, and the fragments with different kinetic energies show peaks at different dissociation angles.

Method of the reduced-added Green function in the calculation of atomic polarizabilities

The Green function in the quantum defect theory provides an exact account for high-excited and continuum electronic states. We modify it by taking into account the ground and low-excited states using their wave functions calculated ab initio. As an application, we present a simple and efficient semianalytical method for the calculation of atomic electric frequency-dependent scalar dipole polarizability, for both real and imaginary frequencies. The polarizabilities calculated for some atoms (Li, Na, K, Be, Mg, Ca, Si, P, S, O, Al, Ge, C, N, F, He, Ne, Ar, Kr, and Xe) are compared with existing methods of computational quantum chemistry and with experiments; good accuracy of the proposed method is demonstrated.

Ultrafast charge transfer and radiationless relaxations from higher excited state (S2) of directly linked Zn-porphyrin (ZP)-acceptor dyads: investigations into fundamental problems of exciplex chemistry

We have investigated photoinduced electron transfer and related processes from the higher excited electronic state (S2) of Zn-porphyrin-imide acceptor directly linked supramolecular systems (ZP-I) designed especially for the critical studies of the energy gap law (EGL) of the charge separation (CS) from the S2 state and solvent effects upon EGL. We have confirmed the modification of the EGL by change of solvent polarity from acetonitrile (ACN), tetrahydrofuran (THF) to toluene (Tol) and methyl-cyclohexane (MCH), from rather typical bell-shaped one in ACN to that with less prominent normal region and prominent inverted region with moderate slope extending over wider range of −ΔGCS values in nonpolar solvent MCH. We have demonstrated that these solvent effects upon EGL affect delicately various radiationless relaxation processes from S2 state. We have examined also effects of the hydrogen bonding solvent ethanol (EtOH) on the EGL for CS and found very specific effect controlling the CS reaction and related processes.

Magnetic and optical properties of single 4f n and mixed 4f n−1 5d electronic configurations of trivalent rare earth ions in wide band gap dielectric crystals

The investigation of the optical and magnetic properties of the rare earth ions in wide band gap fluoride dielectric crystals could trigger a new variety of applications using high excited electronic states. By applying laser-induced fluorescence spectroscopy in the vacuum ultraviolet (VUV) region of the spectrum (100–200 nm), it was found strong emission in the VUV and UV spectral regions due to the strong dipole 4f n−1 5d→4f n interconfigurational transitions of rare earth (RE) ions in wide band gap fluoride crystals. The emitted radiation is highly directional suggesting a strong paramagnetic response of the 4f n−1 5d electronic configuration following VUV laser excitation at 157 nm. In addition, the concentration of the Pr 3+ and Tm 3+ ions in KY 3F 10 and CaF 2 crystal hosts can be accurately evaluated by measuring the magnetic moment of the Pr 3+ and Tm 3+ ions, using the vibrating sample magnetometer method, in a non-destructive way for the first time to our knowledge. Since the efficiency of the laser crystals doped with trivalent RE ions depends on the degree of the homogeneous distribution of the concentration of the trivalent RE ions over the crystal volume, the method can be used to evaluate the quality of the laser crystals.

Internal Conversion and Vibronic Relaxation from Higher Excited Electronic State of Porphyrins: Femtosecond Fluorescence Dynamics Studies

To elucidate the dynamics and mechanisms of radiationless transitions from higher excited electronic states as well as the ultrafast intramolecular vibronic relaxation in porphyrin derivatives, we ...

The microwave spectrum of the cesium monoxide CsO radical

The microwave spectrum of CsO has been observed and analyzed, not only in the ground vibrational state, but also in the v=1–3 excited vibrational states. The CsO radical was generated by the reaction of N2O with Cs vapor, which was produced by the reaction of Li metal with CsCl at 500–530 °C. The observed spectra were found to conform to those expected for a Σ2 diatomic molecule, thereby establishing the ground electronic state of CsO to be of Σ2. The observed rotational and centrifugal distortion constants yielded the equilibrium bond length and the harmonic vibrational frequency to be 2.300 745 (16) Å and 356.78 (11) cm−1, respectively, based on the Born–Oppenheimer approximation. A careful examination of the observed spectral pattern definitely concluded that the spin-rotation interaction constant was positive, at variance with the expectation from a simple Σ2/2Π two-states interaction. This observation was interpreted by assuming positive contributions from higher excited electronic states which superseded a negative contribution from the Π2 lowest excited state; the latter state was responsible for the large dependence of the spin-rotation interaction constant on the vibrational quantum number and was estimated from this vibrational dependence to be located at 1225 cm−1 above the ground electronic state. In reverse to the spin-rotation splitting, the hyperfine splitting was found to increase with the vibrational excitation; in the v=3 state the hyperfine structure was found completely resolved. However, the hyperfine coupling constants did not vary much with the vibrational quantum number, namely the vibrational dependence of the hyperfine splitting was caused primarily by that of the spin-rotation splitting. The observed hyperfine interaction constants indicated that CsO was an ionic molecule.

Photobleaching of Fluorescent Dyes under Conditions Used for Single-Molecule Detection: Evidence of Two-Step Photolysis

The photostability of fluorescent dyes is of crucial importance for the statistical accuracy of single-molecule detection (SMD) and for the image quality of scanning confocal microscopy. Concurrent results for the photostability were obtained by two different experimental techniques. First, the photostabilities of several coumarin and rhodamine derivatives in aqueous solution were obtained by monitoring the steady-state fluorescence decay in a quartz cell. Furthermore, an epi-illuminated microscope, continuous wave (CW) excitation at 514.5 nm, and fluorescence correlation spectroscopy (FCS) with a newly developed theory were used to study the photobleaching characteristics of rhodamines under conditions used for SMD. Depending on the rhodamine structure, the probability of photobleaching, p(b), is in the order of 10(-)(6)-10(-)(7) for irradiances below 10(3) W/cm(2). However, a considerable increase of p(b) for irradiances above this level was observed which can only be described by photobleaching reactions from higher excited states (two-step photolysis). In view of these observations, the probability of photobleaching, p(b), as well as a closed expression of its dependence on the CW excitation irradiance considering a five-level molecular electronic state model with the possibility of photobleaching from higher excited electronic states, is derived. From this model, optimal conditions for SMD with respect to the number of emitted fluorescence photons and to the signal-to-background ratio are discussed, taking into account both saturation and photobleaching. The additional photobleaching due to two-step photolysis limits the applicable irradiance.

A multiphotochromic tetraanthraporphyrazine based on the involvement of molecular singlet oxygen

A photochromic system working in the red-near IR region is described. The photooxygenation of the palladium complex of octaphenyltetraantltra-porphyrazine 1 ( λ max = 846 nm in benzene) in the presence of molecular oxygen is studied by absorption spectroscopy. Species with different absorption behaviour are formed and detected in the spectral range 600–850 nm. The final photoproduct is assigned to be a substituted palladium phthalocyanine 2 containing four trans-annular endoperoxide bridges in the middle part of the anthracene unit. The formation of this photoproduct involves singlet oxygen. Excitation of the photoproduct 2 into higher excited electronic states by UV-laser light results in the release of molecular oxygen and regeneration of the starting molecule 1.

非線形分光法：原理と応用 ＩＶ．高励起電子状態の２波長二重共鳴分光

非線形分光法：原理と応用 ＩＶ．高励起電子状態の２波長二重共鳴分光

The first annulated porphyrazine containing four endoperoxide bridges

Photooxygenation of palladium octaphenyltetraanthraporphyrazine 1 to 2, which is the first example of a porphyrazine containing four endoperoxide bridges in the anthracene unit has a Q-band absorption maximum at 662 nm and exhibits photochromic properties. Irradiation of 2 into higher excited electronic states ( λ exc. < 350 nm) leads to a regeneration of the oxygen-free derivative with λ max = 846 nm due to a cycloreversion.

Photochemical elimination of singlet oxygen from iridium peroxo complexes

Abstract It has been found that Vaska's compound, Ir(CO)CI(PPh 3 2 (O 2 , eliminates singlet oxygen (3%) by irradiation, which is in contrast to results from previous work. Ir(CO)CI(PPh 3 ) 2 (O 2 ) was photolysed by a 308 nm laser pulse in degassed solvents. The singlet oxygen formed was detected by its emission at 1276 nm ( 1 Δ g → 3 Σ − g ). The nature of the emission was confirmed by the dependence of its lifetime on the solvent and the fact that it was quenched in methylene chloride by DABCO with a rate constant of 1 × 10 8 M −1 s −1 . The related complexes Ir(CO)X(PPh 3 ) 2 (O 2 ) (where XBr and I) and [Ir(dppe) 2 (O 2 )]Cl were also examined in respect to produce singlet oxygen by photolysis. With the exception of [Ir(dppe) 2 (O 2 )Cl, small amounts of singlet oxygen could be detected. Additionally, the wavelength dependence of the photolysis quantum yields shows that the observed photoelimination of oxygen obviously occurs from a higher excited electronic state. The excited state responsible for the elimination is likely to possess significant O δ− 2 → Ir δ+ LMCT character.

Higher excited electronic states in clusters of ZnSe, CdSe, and ZnS: Spin-orbit, vibronic, and relaxation phenomena

Metal selenide clusters have been made and characterized, using the arrested precipitation colloidal technique. A comparison of sulfide and selenide spectra enables observation of the effect of changes in the highest occupied molecular orbitals upon cluster electronic properties. The first and second excited electronic states are both observed as a function of size in ZnSe clusters. The systematic dependence of the spectra lead to assignment of the higher state to a 1S-type hole based upon the split-off valence band. It is shown that the energy spectrum of discrete hole states is controlled by the spin-orbit energy and the isotropic hole mass in small, highly symmetrical clusters. This result contrasts with the heavy hole and light hole states observed for planar confinement. In ≂ 20 Å diameter ZnS clusters, there is a strong vibronic temperature dependence in the excited state spectra, while in clusters of smaller gap materials such vibronic effects are very minor. We conjecture that lifetime broadening is severe in clusters of small gap materials.

Rotational spectroscopy of DO2 by FIR LMR and millimeter-wave absorption

Abstract We report the measurement of approximately 50 rotational transitions in the DO 2 radical between 230 and 2530 GHz by high-resolution millimeter-wave and far-infrared laser magnetic resonance spectroscopy. The radical was generated in the gas phase by the reaction of chlorine atoms and oxygen or discharged oxygen with deuterated methanol. The data were analyzed in conjunction with previously published high-resolution spectra of the molecule in the ground vibronic state in order to extract the best set of parameters in the effective Hamiltonian describing the molecule. The fine structure (spin-rotation) parameters derived in the present work were used together with those for HO 2 [A. Charo and F. C. De Lucia, J. Mol. Spectrosc. 94, 426–436 (1982)] in order to determine all of the symmetry-allowed spin-rotation tensor components for the hydroperoxyl radical. The results cannot be interpreted in terms of contamination of the ground state wavefunction by the lowest lying A 2 A state alone and information from quantum chemical calculations of spin-orbit matrix elements between the ground and higher excited states or additional experimental data involving higher excited electronic states are necessary before a complete rationalization of the results is possible.

Multiphoton probing of molecular Rydberg states

This feature article provides an overview of the additional insights that multiphoton excitation methods are providing to our understanding of the spectroscopy and the photophysics of some of the higher excited electronic states of gas phase molecular species.

ChemInform Abstract: PHOTOELECTRON‐PHOTON COINCIDENCE STUDIES OF HALOBENZENE CATIONS IN THEIR EXCITED ELECTRONIC STATES

Fluorescence quantum yields and lifetimes of the cations of 1,3,5‐trichloro‐, 1,3,5‐trichlorotrifluoro, 1,3,5‐tribromotrifluoro‐, 1,4‐dichloro‐, and of 1,3‐dichlorobenzene in selected levels of their B electronic states have been determined. The principle of these measurements is based on the detection of coincidences between photons and energy analyzed photoelectrons following photoionization. These data, obtained under collision free conditions, yield the radiative and nonradiative rate constants for the cations as a function of their internal energy. With the 1,3,5 derivatives, coincidences were also detected when their cations were generated in higher excited electronic states and the wavelength region of the resulting photons could be located. The implications of these observations on the spectroscopic and relaxation behavior of these cations are discussed.