Excited Manifold Research Articles

Solute–solvent intermolecular vibronic coupling as manifested by the molecular near-field effect in resonance hyper-Raman scattering

Vibronic coupling within the excited electronic manifold of the solute all-trans-β-carotene through the vibrational motions of the solvent cyclohexane is shown to manifest as the "molecular near-field effect," in which the solvent hyper-Raman bands are subject to marked intensity enhancements under the presence of all-trans-β-carotene. The resonance hyper-Raman excitation profiles of the enhanced solvent bands exhibit similar peaks to those of the solute bands in the wavenumber region of 21,700-25,000 cm(-1) (10,850-12,500 cm(-1) in the hyper-Raman exciting wavenumber), where the solute all-trans-β-carotene shows a strong absorption assigned to the 1A(g) → 1B(u) transition. This fact indicates that the solvent hyper-Raman bands gain their intensities through resonances with the electronic states of the solute. The observed excitation profiles are quantitatively analyzed and are successfully accounted for by an extended vibronic theory of resonance hyper-Raman scattering that incorporates the vibronic coupling within the excited electronic manifold of all-trans-β-carotene through the vibrational motions of cyclohexane. It is shown that the major resonance arises from the B-term (vibronic) coupling between the first excited vibrational level (v = 1) of the 1B(u) state and the ground vibrational level (v = 0) of a nearby A(g) state through ungerade vibrational modes of both the solute and the solvent molecules. The inversion symmetry of the solute all-trans-β-carotene is preserved, suggesting the weak perturbative nature of the solute-solvent interaction in the molecular near-field effect. The present study introduces a new concept, "intermolecular vibronic coupling," which may provide an experimentally accessible∕theoretically tractable model for understanding weak solute-solvent interactions in liquid.

Vibrational analysis of excited and ground electronic states of all-trans retinal protonated Schiff-bases

We report on vibrational coherence dynamics in excited and ground electronic states of all-trans retinal protonated Schiff-bases (RPSB), investigated by time-resolved Degenerate Four-Wave-Mixing (DFWM). The results show that wave packet dynamics in the excited state of RPSB consist of only low-frequency (<800 cm(-1)) modes. Such low-frequency wave packet motion is observed over a broad range of detection wavelengths ranging from excited state absorption (∼500 nm) to stimulated emission (>600 nm). Our results indicate that low-frequency coherences in the excited state are not activated directly by laser excitation but rather by internal vibrational energy redistribution. This is supported by the observation that similar coherence dynamics are not observed in the electronic ground state. Challenging previous experimental results, we show that the formation of low-frequency coherence dynamics in RPSB does not require significant excess vibrational energy deposition in the excited state vibrational manifolds. Concerning ground state wave packet dynamics, we observe a set of high-frequency (>800 cm(-1)) modes, reflecting mainly single and double bond stretching motion in the retinal polyene-chain. Dephasing of these high-frequency coherences is mode-dependent and partially differs from analogous vibrational dephasing of the all-trans retinal chromophore in a protein environment (bacteriorhodopsin).

Crystal field fine spectroscopy of trivalent terbium in yttrium aluminum borate single crystals

Tb3+ doped single crystals of huntite-type YAl3(BO3)4 (YAB) have been characterized by means of Fourier transform absorption spectroscopy in the wave number range 500-25000 cm−1 and in the temperature range 9-300 K, and by means of 9 K linear dichroism measurements. Crystal-field splitting of the fundamental 7F6 and of the excited 7F5, 7F4, 7F3, 7F2, 7F1, 7F0, and 5D4 manifolds of Tb3+ have been analyzed and fitted within a single ion Hamiltonian model, to obtain free-ion and crystal-field parameters. The electron-phonon interaction has been put into evidence by thermally induced line shift and discussed in the framework of a single phonon coupling model.

Insights into the orbital invariance problem in state-specific multireference coupled cluster theory

In this communication we report the results of our studies on the orbital invariance properties of the state-specific multireference coupled cluster approach suggested by Mukherjee and co-workers (Mk-MRCC). In particular, we have gathered numerical evidence to show that even when the linear excitation manifold is modified in order to span the same space for each reference, the resulting method is not orbital invariant. In order to test this conjecture we have proposed a new truncation scheme (Mk-MRCCSDtq) which, in addition to full single and double excitations, contains partial triple and quadruple excitations. For a reference space generated by all possible combinations of two electrons in two orbitals, the linear excitation manifold of Mk-MRCCSDtq spans the same set for each reference determinant. Mk-MRCCSDtq is found to lack energy invariance for rotations among active molecular orbitals but it is less sensitive to orbital rotations than the conventional scheme which includes only singles and doubles (Mk-MRCCSD). Nevertheless, Mk-MRCCSDtq is a very accurate method, superior with respect to multireference configuration interaction approaches, and competitive with the active-space coupled cluster method and the MRexpT ansatz.

A quantum differentiation of k-SAT instances

We present a quantum adiabatic algorithm to differentiate between k-SAT instances, those with no solutions and those that have many solutions. The time complexity of the algorithm is a function of the energy gap between the subspace of all 0-eigenvectors (ground states) and the first excited states manifold, and scales polynomially with the number of resources. The idea of gaps between subspaces suggests a new tool to analyze time complexity in adiabatic quantum machines.

Photoisomerization in a Platinum−Amido Pincer Complex: An Excited-State Reaction Pathway Controlled by Localized Ligand Photochemistry

Computational investigations of the electronic spectroscopy and photochemical isomerization in the complex (bis(8-quinolinyl)amido)PtMe2I are presented. Time-dependent density functional theory, in conjunction with the polarizable continuum solvent model, reproduce the experimental spectra for the mer and fac isomers well. The nature of the initially populated states for the mer isomer are ππ* in nature and localized on the BQA ligand. Geometry optimization shows that the system relaxes in the excited manifold to a fac-like geometry in the S1 electronic state. Complete active space self-consistent field (CASSCF) calculations show that there exists a sloped conical intersection that connects the excited- and ground-state fac species, allowing for radiationless deactivation in fac-like geometries.

Purely-long-range krypton molecules in singly and doubly excited binding potentials

Diatomic potentials for krypton are computed and also probed experimentally. For a probe-laser wavelength near 811 nm, several strong dipole-dipole interactions produce purely-long-range potential wells in the singly excited manifold of (s+p) potentials and in the doubly excited manifold of (p+p) and (s+d) potentials. Evidence of resonant photoassociation into bound states of these potential wells is observed in the emission of ions and ultraviolet photons from a magneto-optically trapped krypton cloud.

Excited States of [3.3](4,4′)Biphenylophane: The Role of Charge-Transfer Excitations in Dimers With π−π Interaction

The singlet and triplet electronic excitation manifold of [3.3](4,4')biphenylophane (BPP), an intramolecular dimer, and 4,4'-dimethylbiphenyl (DMBP), the corresponding monomer, has been analyzed by employing the approximate coupled-cluster singles and doubles model (CC2). The calculated triplet-triplet and singlet-singlet transient absorption spectra show good agreement with recent experimental results. The calculations suggest a strong interaction of the two biphenyl moieties of BPP in the first singlet and triplet excited states due to the overlapping pi-electron systems, and Forster-Dexter theory for weak coupling cannot be applied. Both the first excited singlet and triplet states of BPP can be characterized as excimeric states with a strong admixture of charge-transfer contributions.

Triplet formation of 6-azauridine and singlet oxygen sensitization with UV light irradiation

Excited state characteristics of 6-azauridine (6AUd), which is known as a medicine against psoriasis and neoplastic, were investigated with laser plash photolysis, time-resolved thermal lensing, and near IR single photon counting method. The triplet-triplet absorption spectrum of 6AUd was observed for the first time. The formation quantum yield of excited triplet 6AUd (Phi(ISC)) was estimated by acetone triplet sensitization and actinometry with benzophenone to be 1.00 +/- 0.07 (248 nm excitation) and 0.78 +/- 0.05 (308 nm excitation). This excitation wavelength effect could be explained by intersystem crossing (ISC) to the excited triplet manifolds occurring during the relaxation on the potential energy surface (PES) of the S(1)(npi*) state and be in competition with internal conversion to the S(0) state after the relaxation to the minimum of the S(1)(npi*) state. 6AUd had a lower Phi(ISC) value than 6-azauracil (6AU) with the 308 nm excitation (Phi(ISC) = 0.93 +/- 0.04 for 6AU). The nucleoside has more vibrational modes than 6AU, and therefore the ribose would accelerate intramolecular vibrational energy redistribution and the relaxation to the minimum of the PES of the S(1)(npi*) state. Sensitized singlet oxygen formation of 6AUd was also detected in the O(2)-saturated condition with quantum yields of 0.49 +/- 0.01 with the 248 nm excitation, indicating the high phototoxicity of 6AUd.

Probing intermolecular couplings in liquid water with two-dimensional infrared photon echo spectroscopy

Two-dimensional infrared photon echo and pump probe studies of the OH stretch vibration provide a sensitive probe of the correlations and couplings in the hydrogen bond network of liquid water. The nonlinear response is simulated using numerical integration of the Schrodinger equation with a Hamiltonian constructed to explicitly treat intermolecular coupling and nonadiabatic effects in the highly disordered singly and doubly excited vibrational exciton manifolds. The simulated two-dimensional spectra are in close agreement with our recent experimental results. The high sensitivity of the OH stretch vibration to the bath dynamics is found to arise from intramolecular mixing between states in the two-dimensional anharmonic OH stretch potential. Surprisingly small intermolecular couplings reproduce the experimentally observed intermolecular energy transfer times.

Intensity analysis and crystal-field modeling of Ho3+ in KPb2Cl5 host

Optical absorption and emission intensities are investigated for Ho3+ doped into single-crystal KPb2Cl5. Room temperature absorption spectra of Ho3+(4f10), representing transitions from I58 to excited multiplet manifolds observed between 400 and 2100 nm, have been analyzed using the Judd–Ofelt (JO) model to obtain the phenomenological intensity parameters Ω2, Ω4, and Ω6. The JO intensity parameters are used to calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios of the Ho3+ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds L2S+1J of Ho3+. The room temperature fluorescence spectrum in the near infrared region is reported between 850 and 1550 nm. The emission cross section for the intermanifold transition, F55→I57 (0.98 μm) has been determined. The 8 K absorption spectrum was examined as well. The detailed structure observed in the absorption bands I57, S52, F54, and F53, was analyzed in terms of the crystal-field splitting of each manifold using a charge-compensation model first developed for Er3+ doped into KPb2Cl5. The optical and spectroscopic characteristics of Ho3+:KPb2Cl5 demonstrate that this material has potential as a laser host system at various wavelengths.

Circular dichroism of helical structures using semiempirical methods

A general semiempirical scheme has been elaborated to simulate circular dichroism (CD) spectra of supramolecular systems. This approach adopts the analytical method of Beck and Hohlneicher [Theor. Chem. Acc. 101, 297 (1999).] to evaluate the one- and two-center integrals over Slater atomic orbitals. The performance of the method, employing INDO/S and CNDO/S semiempirical parametrizations, has been assessed by considering (i) the effect of the size of the singly excited states manifold, (ii) the origin invariance, and (iii) comparisons with the experimental and other theoretical spectra of several helicenes as well as pyridine-pyrimidine oligomers, which can adopt helical conformations. The main results are (i) the INDO/S parametrization with rather small excitation manifolds is able to reproduce, at low computational costs, the experimental CD spectra of several helicenes as well as CD simulations performed at ab initio and time-dependent density functional theory level of approximation; (ii) in the series of homohelicenes, the rotatory strength of the lowest-energy band increases almost linearly with the size of the helix; (iii) as evidenced by the study of tetradodecyloxy helicene bisquinone, packing effects can change the sign of remarkable CD bands, which are used to assign the structure configuration.

Characterization of 4I9/2 ↔ 4F3/2 optical transitions in trivalent Nd3+ ions in GaLaS glass

The positions of Stark levels have been determined, using a step-by-step procedure, in the 4I9/2 and 4F3/2 manifolds of Nd3+ ions from absorption and photoluminescence measurements in the 12–293 K temperature range. This data has been used to calculate the emission cross-section for which the maximum value turns out to be ∼2.3 × 10−20 cm2. The radiative recombination time, calculated using Judd–Ofelt analysis, of the 4F3/2 manifold is in close vicinity to the experimentally determined times that were measured by the conventional decay of PL after interruption of excitation and by QFRS. Moreover, the peak time defined by QFRS is independent of temperature. Therefore, the dominant relaxation mechanism from the 4F3/2 excited manifold of Nd3+ ions in GaLaS glass is believed to be by radiative emission.

Spectral analysis of synthesized nanocrystalline aggregates of Er3+:Y2O3

The absorption and fluorescence spectra of nanocrystalline aggregates of Y2O3 doped with Er3+ are reported between 8K and room temperature. The nanocrystalline particles were synthesized from a homogenous solution of the metal ions and urea at elevated temperatures in order to control the precipitation of the mixed hydroxides by a slow uniform reaction throughout the solution. The morphology of the calcinated materials revealed uniformly spherical aggregates 200nm or less depending on the ratio of the metal ions in the initial solution. Spectra obtained from these particles were analyzed in detail for the crystal-field splitting of the LJ2S+1 multiplet manifolds of Er3+(4f11) including the ground-state manifold I15∕24, and excited manifolds I9∕24, F9∕24, S3∕24, H11∕22, F7∕24, F5∕24, and F3∕24. Fluorescence lifetimes and results from an analysis of the intensities of manifold-to-manifold transitions are also reported. The sharp-line absorption and emission spectra are comparable to spectra reported earlier for Er3+:Y2O3 grown as large single crystals by a flame fusion method. The results described in the present study suggest that the simple, inexpensive method of preparation that is reported will lead to further investigation of these nanocrystals for their optical properties, especially in the near infrared region of the spectrum.

Modeling the crystal-field splitting of energy levels of Er3+(4f11) in charge-compensated sites of KPb2Cl5

A point-charge lattice-sum model corrected for induced multipoles is used to investigate the crystal-field splitting of the LJ2S+1 energy levels of Er3+(4f11) ions that occupy charge-compensated sites in the laser host crystal KPb2Cl5. Spectroscopic data are reported and analyzed for Er3+ between 1550 and 440nm at cryogenic temperatures. The crystal-field (Stark) splitting of the ground-state manifold I15∕24 and the splitting of individual excited manifolds of Er3+ are established from analyses of temperature-dependent (hot band) absorption spectra. The analyses confirm the Stark splitting of the IJ4 and F9∕24 manifolds that are reported in the literature. From an analysis of the data, it appears that only one of the two possible Pb2+ sites serving as a charge-compensated site for Er3+ is involved in the optical activity of the Er3+ ions. From an examination of the crystallographic data of KPb2Cl5, we identify a possible site for the optically active Er3+ ion in the lattice and calculate the lattice-sum components for that site. These components are used to evaluate the crystal-field splitting of the energy levels of Er3+ at that site. The charge-compensation model assumes that Er3+ substitutes for Pb2+ in the Pb(2) site with a vacancy in a nearby K+ site. To obtain the best overall agreement between calculated and experimental levels, the position of the Er3+ ion is treated as an adjustable parameter along the quantization axis. Individual manifold centroids of the Er3+ ion are also varied. From a least-squares fitting analysis, we obtain a rms deviation of 10cm−1 between 48 calculated-to-observed Stark levels.

Energy levels and intensity parameters of ions in Y3Al5O12 and Lu3Al5O12

The energy levels of the trivalent lanthanide Ho3+ in Y3Al5O12 (YAG) and Lu3Al5O12 (LuAG) have been measured. The Stark split levels for the first nine Ho manifolds in these materials have been measured, and the results have been fit to a free ion plus crystal field Hamiltonian to generate a theoretical set of energy levels. Crystal field parameters were varied to determine the best fit between experimental and theoretical energy levels. The energy levels of Ho:LuAG are seen to be very similar to those in Ho:YAG. However, subtle changes resulting from replacing Y3+ with Lu3+ in the garnet crystal Y3Al5O12 result in different transition wavelengths in LuAG. This has implications for Ho I75→I85 lasers operating at ∼2.1μm. Although the energy levels have been measured previously in Ho:YAG, they have not been measured in Ho:LuAG. A comparison of the energy levels in Ho:YAG measured here show some discrepancies with previous measurements. The consistency of the energy level placements between Ho:LuAG and Ho:YAG indicate that the earlier studies may have some errors in the assignments. Finally, a Judd–Ofelt analysis is performed on Ho:YAG and Ho:LuAG to determine the intensity parameters, and thus, the transition probabilities and branching ratios of the first eight excited manifolds.

Use of Ultrafast Dispersed Pump−Dump−Probe and Pump−Repump−Probe Spectroscopies to Explore the Light-Induced Dynamics of Peridinin in Solution

Optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol was studied by dispersed pump-probe, pump-dump-probe, and pump-repump-probe transient absorption spectroscopy in the visible region. Dispersed pump-probe measurements show that the decay of the initially excited S2 state populates two excited states, the S1 and the intramolecular charge-transfer (ICT) state, at a ratio determined by the excitation wavelength. The ensuing spectral evolution occurs on the time scale of a few picoseconds and suggests the equilibration of these states. Dumping the stimulated emission of the ICT state with an additional 800-nm pulse after 400- and 530-nm excitation preferentially removes the ICT state contribution from the broad excited-state absorption, allowing for its spectral characterization. At the same time, an unrelaxed ground-state species, which has a subpicosecond lifetime, is populated. The application of the 800-nm pulse at early times, when the S2 state is still populated, led to direct generation of the peridinin cation, observed for the first time in a transient absorption experiment. The excited and ground electronic states manifold of peridinin has been reconstructed using target analysis; this approach combined with the measured multipulse spectroscopic data allows us to estimate the spectra and time scales of the corresponding transient states.

Er3+-doped tellurofluorophosphate glasses for lasers and optical amplifiers

Absorption, fluorescence and decay properties of erbium-doped alkalitellurofluorophosphate glasses (RTFP) with the molar compositions of50 (NaPO3)6–10 TeO2–20 AlF3–19 RF–1 Er2O3 (R = Li,Na or K) have been investigated in order to utilize these materials for the development of fibreamplifiers and lasers. The Judd–Ofelt (JO) model was applied to the absorption intensities ofEr3+ (4f11) transitions to determine the JO intensity parametersΩλ (λ = 2,4 or 6). These evaluated intensity parameters are used to calculate thespontaneous emission probabilities and branching ratios from the excited stateJ manifolds tothe lower lying J′ manifolds of Er3+ emission transitions. The radiative lifetimes of these excited states are determined from their respectivespontaneous emission probabilities. Visible and NIR emission spectra have been studied for all threeEr3+-doped tellurofluorophosphate glasses. In particular, for the emission at1.5 µm corresponding to the transition, radiative parameters like the full width at half maximum (FWHM), emission cross-sections(σe) and figureof merit (FWHM × σe) were determined and compared with other hosts. The measured lifetimes of the4S3/2 level are compared with predicted radiative lifetimes calculated from the JO theory. The potentialityof Er3+-doped tellurofluorophosphate glasses for devices such as lasers and optical amplifiers isdiscussed.

Spectroscopic characterisation of the Tm3+ doped KLa(WO4)2 single crystals

Abstract The spectroscopic characterisation of the Tm3+ doped double potassium–lanthanum tungstate KLa(WO4)2 (KLWO) through the absorption, fluorescence and lifetime measurements is presented. We show absorption spectra in the visible and NIR regions recorded at room and low temperature, the luminescence spectra especially that of the 3H4 → 3H6 transition lying in the 800 nm region which makes it suitable for diode laser pumping. The lifetimes were measured for KLa(WO4)2 with 2 at.% of Tm3+ and the values were 112 μs, 208 μs, 1.7 ms and 5.7 μs for 1G4, 3H4, 3F4, and 1D2, respectively. The results of the Judd–Ofelt analysis are presented and discussed. The obtained intensity parameters were used to determine the radiative decay rates, radiative lifetimes and branching ratios for the Tm3+ transitions from the excited multiplet manifolds to the lower lying manifold states. The infrared cross-section measurements were done.

Absolute electronic excitation cross sections for low-energy electron (5–12eV) scattering from condensed thymine

The absolute cross sections for electronic excitations of thymine by electron impact between 5 and 12 eV are determined by means of electron-energy loss (EEL) spectroscopy for the molecule deposited at submonolayer coverage on an inert Ar substrate. The lowest EEL features at 3.7 and 4.0 eV are attributed to the excitation of the triplet 1 3A'(pi --> pi*) and 1 3A''(n --> pi*) valence states of the molecule. The higher EEL features located at 4.9, 6.3, 7.3, and 9 eV with a weak shoulder around 6 eV are ascribed mostly to triplet valence (pi --> pi*) excitation manifold of the molecule. The energy dependence of the cross section for both the lowest triplet valence excitations shows essentially a peak at about 5 eV reaching a value of 2.9 x 10(-17) cm2. The cross sections for the higher EEL features are generally characterized by a common broad maximum around 8 eV. The latter reaches a value of 1.36 x 10(-16) cm2 for the combined 6 and 6.3 eV excitation region. The maxima in the present cross sections are found to correspond to the resonances that have been reported at about the same energies in the O- yield from electron impact on thymine in the gas phase.