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Photofragmentation electronic spectra of isolated single-isomeric N-protonated quinoline (quinolinium) and isoquinoline (isoquinolinium) ions have been measured at a temperature of ~40 K using a mass-selective, 10 cm-1 spectral resolution, photodissociation spectrometer. Additionally, ab initio adiabatic transition energies calculated using the RI-ADC(2) method have been employed to assist in the assignment of the spectra. Three electronic transitions having ππ* character were clearly evidenced for both protonated ions within the UV and deep-UV spectral ranges. The corresponding spectra at room temperature were previously reported by Hansen et al., together with TD-DFT calculations and a careful analysis of the possible fragmentation mechanisms. This information will be complemented in the present study by appending better resolved spectra, characteristic of cold ions, in which well-defined vibrational progressions associated with the S1 ← S0 and S3 ← S0 transitions exhibit clear 0-0 bands at hν0-0 = 27868 and 42230 cm-1, for protonated quinoline, and at hν0-0 = 28043 and 41988 cm-1, for protonated isoquinoline. Active vibrations in the spectra were assigned with the help of calculated normal modes, looking very similar to those of the structurally related protonated naphthalene. Finally, we have observed that the bandwidths associated with the deep-UV S3 ← S0 transition denote a lifetime for the S3 excited state in the subpicosecond time scale, in contrast with that of S1. [ABSTRACT FROM AUTHOR]

The lowest two electronically excited singlet states of indole and its derivatives are labeled as La or Lb, based on the orientation of the transition dipole moment (TDM) and the magnitude of the permanent electric dipole moment. Rotationally resolved electronic Stark spectroscopy in combination with high level ab initio calculations offers the possibility to determine these characteristics and thus the electronic nature of the excited states. In the present contribution this approach was pursued for the systems 4- and 6-fluoroindole and the results compared to the previously investigated system 5-fluoroindole. Changing the position of the fluorine atom from 5 to 4 or 6 is accompanied by an increasing amount of La character in the S1 state. This dramatically influences the orientation of the TDM and erases its ability to be a reasonable identifier of the nature of the excited states for both molecules. However, for 4-fluoroindole, where the influence of the La is weak, the nature of the S1 state can still be assigned to be mainly Lb based on the excited state dipole moment. For 6-fluoroindole, this is not the case anymore, and the La/Lb nomenclature completely breaks down due to heavily mixed excited states. [ABSTRACT FROM AUTHOR]

A model for simulating the transient electronic absorption spectra of donor-acceptor dyads undergoing ultrafast intramolecular charge transfer in solution has been developed. It is based on the stochastic multichannel point-transition approach and includes the reorganization of high-frequency intramolecular modes (treated quantum mechanically) and of low frequency intramolecular and solvent modes (described classically). The relaxation of the slow modes is assumed to be exponential with time constants taken from experiments. The excited-state dynamics is obtained by simulating the population distribution of each quantum state after optical excitation and upon electronic and vibrational transitions. This model was used to simulate the transient electronic absorption spectra measured previously with a pyrylium phenolate in acetonitrile. A very good agreement between the simulated and measured spectra was obtained assuming a three-level model including the ground state, the optically excited state, and a dark state with large charge-transfer character and a substantially different geometry relative to that of the optically excited state. The merit of this approach to disentangle the contributions of both population changes and relaxation processes to the ultrafast spectral dynamics will be discussed. [ABSTRACT FROM AUTHOR]

We report the electronic spectra of mass selected [(bpy)(tpy)Ru-OH2]2+·(H2O)n clusters (bpy = 2,2′-bipyridine, tpy =2,2′:6′2″-terpyridine, n = 0-4) in the spectral region of their metal-to-ligand charge transfer bands. The spectra of the mono- and dihydrate clusters exhibit partially resolved individual electronic transitions. The water network forming at the aqua ligand leads to a rapid solvatochromic shift of the peak of the band envelope: addition of only four solvent water molecules can recover 78% of the solvatochromic shift in bulk solution. The sequential shift of the band shows a clear change in behavior with the closing of the first hydration shell. We compare our experimental data to density function theory (DFT) calculations for the ground and excited states. [ABSTRACT FROM AUTHOR]

The electronic and infrared spectra of the 5-methyl-2-furanylmethyl (MFM) radical have been characterized under jet-cooled conditions in the gas phase. This resonance-stabilized radical is formed by H atom loss from one of the methyl groups of 2,5-dimethylfuran (DMF), a promising second-generation biofuel. As a resonance-stabilized radical, it plays an important role in the flame chemistry of DMF. The D0-D1 transition was studied using two-color resonant two-photon ionization (2C-R2PI) spectroscopy. The electronic origin is in the middle of the visible spectrum (21934 cm-1 = 455.9 nm) and is accompanied by Franck-Condon activity involving the hindered methyl rotor. The frequencies and intensities are fit to a one-dimensional methyl rotor potential, using the calculated form of the ground state potential. The methyl rotor reports sensitively on the local electronic environment and how it changes with electronic excitation, shifting from a preferred ground state orientation with one CH in-plane and anti to the furan oxygen, to an orientation in the excited state in which one CH group is axial to the plane of the furan ring. Ground and excited state alkyl CH stretch infrared spectra are recorded using resonant ion-dip infrared (RIDIR) spectroscopy, offering a complementary view of the methyl group and its response to electronic excitation. Dramatic changes in the CH stretch transitions with electronic state reflect the changing preference for the methyl group orientation. [ABSTRACT FROM AUTHOR]

Electronic spectra of C6H are measured in the 18 950-21 100 cm-1 domain using cavity ring-down spectroscopy of a supersonically expanding hydrocarbon plasma. In total, 19 (sub)bands of C6H are presented, all probing the vibrational manifold of the B²Π electronically excited state. The assignments are guided by electronic spectra available from matrix isolation work, isotopic substitution experiments (yielding also spectra for 13C6H and C6D), predictions from ab initio calculations, and rotational fitting and vibrational contour simulations using the available ground state parameters as obtained from microwave experiments. Besides the 00 0 origin band, three nondegenerate stretching vibrations along the linear backbone of the C6H molecule are assigned: the ν6 mode associated with the C-C bond vibration and the ν4 and ν3 modes associated with CC triple bonds. For the two lowest ν11 and ν10 bending modes, a Renner-Teller analysis is performed identifying the μ²Σ(ν11) and both μ²Σ(ν10) and κ²Σ(ν10) components. In addition, two higher lying bending modes are observed, which are tentatively assigned as μ²Σ(ν9) and μ²Σ(ν8) levels. In the excitation region below the first nondegenerate vibration (ν6), some ²Π-²Π transitions are observed that are assigned as even combination modes of low-lying bending vibrations. The same holds for a ²Π ²Π transition found above the ν6 level. From these spectroscopic data and the vibronic analysis a comprehensive energy level diagram for the B²Π state of C6H is derived and presented. [ABSTRACT FROM AUTHOR]

The Fenna-Matthews-Olson (FMO) trimer (composed of identical subunits) from the green sulfur bacterium Chlorobaculum tepidum is an important protein model system to study exciton dynamics and excitation energy transfer (EET) in photosynthetic complexes. In addition, FMO is a popular model for excitonic calculations, with many theoretical parameter sets reported describing different linear and nonlinear optical spectra. Due to fast exciton relaxation within each subunit, intermonomer EET results predominantly from the lowest energy exciton states (contributed to by BChl a 3 and 4). Using experimentally determined shapes for the spectral densities, simulated optical spectra are obtained for the entire FMO trimer. Simultaneous fits of low-temperature absorption, fluorescence, and hole-burned spectra place constraints on the determined pigment site energies, providing a new Hamiltonian that should be further tested to improve modeling of 2D electronic spectroscopy data and our understanding of coherent and dissipation effects in this important protein complex. [ABSTRACT FROM AUTHOR]

Tetrapyrrole-based pigments play a crucial role in photosynthesis as principal light absorbers in light-harvesting chemical systems. As such, accurate theoretical descriptions of the electronic absorption spectra of these pigments will aid in the proper description and understanding of the overall photophysics of photosynthesis. In this work, time-dependent density functional theory (TD-DFT) at the CAM-B3LYP/6-31G* level of theory is employed to produce the theoretical absorption spectra of several tetrapyrrole-based pigments. However, the application of TD-DFT to large systems with several hundreds of atoms can become computationally prohibitive. Therefore, in this study, TD-DFT calculations with reduced orbital spaces (ROSs) that exclude portions of occupied and virtual orbitals are pursued as a viable, computationally cost-effective alternative to conventional TD-DFT calculations. The effects of reducing orbital space size on theoretical spectra are qualitatively and quantitatively described, and both conventional and ROS results are benchmarked against experimental absorption spectra of various tetrapyrrole-based pigments. The orbital reduction approach is also applied to a large natural pigment assembly that comprises the principal light-absorbing component of the reaction center in purple bacteria. Overall, we find that TD-DFT calculations with proper and judicious orbital space reductions can adequately reproduce conventional, full orbital space, TD-DFT results of all pigments studied in this work. [ABSTRACT FROM AUTHOR]

Properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF4- anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutral 19-electron radical, whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ~0.1 V upon going from 1 to 1a. Unsuccessful attempts to prepare several other aryl substituted derivatives of 1 by the classical synthetic route are described in the Supporting Information. [ABSTRACT FROM AUTHOR]

An effective time dependent approach based on a method that is similar to the Gaussian wave packet propagation (GWP) technique of Heller is developed for the computation of vibrationally resolved electronic spectra at finite temperatures in the harmonic, Franck-Condon/Hertzberg-Teller approximations. Since the vibrational thermal density matrix of the ground electronic surface and the time evolution operator on that surface commute, it is possible to write the spectrum generating correlation function as a trace of the time evolved doorway state. In the stated approximations, the doorway state is a superposition of the harmonic oscillator zero and one quantum eigenfunctions and thus can be propagated by the GWP. The algorithm has an O(N3) dependence on the number of vibrational modes. An application to pyrene absorption spectrum at two temperatures is presented as a proof of the concept. [ABSTRACT FROM AUTHOR]

We report electronic spectra of a series of ruthenium polypyridine complexes of the form [(trpy)(bipy)RuII-L]2+ (bipy = 2,2'-bipyridine and trpy = 2,2':6',2"-terpyridine), where L represents a small molecular ligand that occupies the last coordination site. Species with L = H2O, CO2, CH3CN, and N2 were investigated in vacuo using photodissociation spectroscopy. All species exhibit bright metal-to-ligand charger transfer (MLCT) bands in the visible and near UV, but with different spectral envelopes and peak energies, encoding the influence of the ligand L on the electronic structure of the complex. Several individual electronic bands can be resolved for L = H2O and CO2, while the spectra for L = N2 and CH3CN are more congested, even at low ion temperatures. The experimental results are discussed in the framework of time-dependent density functional theory. [ABSTRACT FROM AUTHOR]

The ground and many excited states of the Mg+He van der Waals molecular system have been explored using a one-electron pseudopotential approach. In this approach, effective potentials are used to consider the Mg2+ core and the electron-He effects. Furthermore, a core-core interaction is included. This has reduced the number of active electrons of the Mg+He, to be considered in the calculation, to a single valence electron. This has permitted to use extended Gaussian basis sets for Mg and He. Therefore, the potentianl energy and dipole moments calculations are carried out at the Hartree-Fock level of theory, and the spin-orbit effect is included using a semiclassical approach. The core-core interaction for the Mg2+He ground state is included using accurate CCSD(T) calculations. The spectroscopic constants of the Mg+He electronic states are extracted and compared with the existing theoretical works, where very good agreement is observed. Moreover, the transition dipole function has been determined for a large and dense grid of internuclear distances including the spin-orbit effect. [ABSTRACT FROM AUTHOR]

Extending our earlier studies on cyclophanes, we here report the structure, chemical shifts, spin-spin coupling constants, absorption and emission properties of [m.n]paracyclophanes, m, n = 2-4, obtained using a combination of experimental and computational techniques. Accurate values of proton chemical shifts as well as of JHH for the bridges are determined. The experimental chemical shifts, coupling constants, absorption and emission wavelengths are satisfactorily reproduced using density functional theory calculations, using both the B3LYP and ?B97X-D functionals. The geometries predicted using a functional that includes dispersion corrections (?B97X-D) are in a better agreement with available experimental values than those obtained using the B3LYP method. Up to 8 UV-vis absorption/emission bands have been observed (or anticipated in the region below 200 nm) and assigned on the basis of quantum-chemical calculations. Optimized excited-state geometries showed that the distances between the aromatic bridgehead carbon atoms of all the [m.n]paracyclophanes in the excited state decrease compared to the ground-state geometries by ca. 0.2-0.9 Å, the largest being for [4.4]paracyclophane, though the rather large differences in the calculated emission wavelength compared to experiment cast some doubts on the accuracy of the excited-state geometries. [ABSTRACT FROM AUTHOR]

Using an ab initio approach based on nonempirical pseudopotentials for the Mg2+ and Li+ cores, Gaussian basis sets, effective core polarization potentials and full configuration interaction calculations, the adiabatic potential energy curves, the spectroscopic constants, the permanent and transition electric dipole moments of the several lowest electronic states of the alkali-alkaline earth ion MgLi+ have been performed. These states dissociate into Mg+(3s and 3p) + Li (2s, 2p, 3s, 3p, 3d, 4s, 4p, and 4d) and Mg (3s², 3s3p, 3s4s, 3s3d, 3s4p, 3s5s, and 3s4d) + Li+. The spectroscopic constants (Re, De, Te, ωe, ωexe, and Be) of the ground state and nearly 53 excited states of 1,3Σ+, 1,3Π, and 1,3Δ symmetries are derived. Most of them are computed for the first time. Moreover, several avoided crossings between the electronic states of 1,3Σ+, 1,3Π symmetries are localized and analyzed. Their existence is related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Mg+Li and MgLi+. Furthermore, accurate adiabatic permanent and transition dipole moments for several transitions have been calculated for a large and dense grid of internuclear distances for the first 15 ¹Σ+ electronic states. A linear behavior is observed in the permanent dipole moments for several electronic states. Additionally, the transition electric dipole moments between neighbor states have shown many peaks situated around the avoided crossing positions. [ABSTRACT FROM AUTHOR]

Transient electronic and vibrational absorption spectroscopy unravel the mechanisms and dynamics of bimolecular reactions of CN radicals with acetone in deuterated chloroform solutions. The CN radicals are produced by ultrafast ultraviolet photolysis of dissolved ICN. Two reactive forms of CN radicals are distinguished by their electronic absorption bands: "free" (uncomplexed) CN radicals, and "solvated" CN radicals that are complexed with solvent molecules. The lifetimes of the free CN radicals are limited to a few picoseconds following their photolytic production because of geminate recombination to ICN and INC, complexation with CDCl3 molecules, and reaction with acetone. The acetone reaction occurs with a rate coefficient of (8.0 ± 0.5) × 1010 M-1 s-1 and transient vibrational spectra in the C-N and C-O stretching regions reveal that both the nascent HCN and 2-oxopropyl (CH3C(O)CH2) radical products are vibrationally excited. The rate coefficient for the reaction of solvated CN with acetone is 40 times slower than for free CN, with a rate coefficient of (2.0 ± 0.9) × 109 M-1 s-1 obtained from the rise in the HCN product v1(C-N stretch) IR absorption band. Evidence is also presented for CN complexes with acetone that are more strongly bound than the CN-CDCl3 complexes because of CN interactions with the carbonyl group. The rates of reactions of these more strongly associated radicals are slower still. [ABSTRACT FROM AUTHOR]

Center line slope (CLS) analysisin 2D infrared spectroscopy has been extensively used to extract frequency–frequencycorrelation functions of vibrational transitions. We apply this conceptto 2D electronic spectroscopy, where CLS is a measure of electronicgap fluctuations. The two domains, infrared and electronic, possessdifferences: In the infrared, the frequency fluctuations are classical,often slow and Gaussian. In contrast, electronic spectra are subjectto fast spectral diffusion and affected by underdamped vibrationalwavepackets in addition to Stokes shift. All these effects resultin non-Gaussian peak profiles. Here, we extend CLS-analysis beyondGaussian line shapes and test the developed methodology on a solvatedmolecule, zinc phthalocyanine. We find that CLS facilitates the interpretationof 2D electronic spectra by reducing their complexity to one dimension.In this way, CLS provides a highly sensitive measure of model parametersdescribing electronic–vibrational and electronic–solventinteraction. [ABSTRACT FROM AUTHOR]

We refine analytical representationsof the potential energy surfaces for the 1 2A′,2 2A′, and 1 2A″ electronic statesof BeOH in simultaneous least-squares fittings of experimental and ab initiodata. These optimizations are carried out withthe MORBID and RENNER programs, using input data from Mascaritolo,Merritt, Heaven, and Jensen (Experimental and Theoretical Characterization of the 22A′-12A′ Transition of BeOH/D. J. Phys. Chem. A.2013, 117, 13654−13663). Withthe refined potential energy surfaces, we make predictions of energylevels for BeOH/D that have not been experimentally determined sofar. We hope that these predictions will permit further assignmentsto be made in the electronic spectra of BeOH/D. [ABSTRACT FROM AUTHOR]

The electronic spectroscopy of isolated toluene in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 4.0-10.8 eV energy range, with absolute cross-section measurements derived. We present the first set of ab initio calculations (vertical energies and oscillator strengths), which we use in the assignment of valence and Rydberg transitions of the toluene molecule. The spectrum reveals several new features not previously reported in the literature, with particular relevance to 7.989 and 8.958 eV, which are here tentatively assigned to the p*(17a') ? s(15a') and 1p*(10a?) ? 1p(14a') transitions, respectively. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of toluene in the upper stratosphere (20-50 km). [ABSTRACT FROM AUTHOR]

The structural, electronic, and spectroscopicproperties of methanediolin aqueous solutions have been studied by a combined approach basedon Car–Parrinello molecular dynamics simulations and ab initiocalculations. The hydrogen bond interactions between the solute andwater have been characterized, showing the important role of the solventin the stabilization of the methanediol conformers in solution. Firstinsights on the experimental vibrational spectra have been obtainedby the analysis of the simulation results, with particular regardto the most prominent band at 1050 cm–1that hasbeen attributed to both the symmetric and antisymmetric CO stretchingmodes. The assignment has been completed adopting both electric andmechanical anharmonic calculations considering the interactions withthe solvent using a polarizable continuum model. [ABSTRACT FROM AUTHOR]

The vibronic coupling model of Köppel,Domcke, and Cederbaum is a powerful means to understand, predict,and analyze electronic spectra of molecules, especially those thatexhibit phenomena that involve breakdown of the Born–Oppenheimerapproximation. In this work, we describe a new parallel algorithmfor carrying out such calculations. The algorithm is conceptuallyfounded upon a “stencil” representation of the requiredcomputational steps, which motivates an efficient strategy for coarse-grainedparallelization. The equations involved in the direct-CI type diagonalizationof the model Hamiltonian are presented, the parallelization strategyis discussed in detail, and the method is illustrated by calculationsinvolving direct-product basis sets with as many as 17 vibrationalmodes and 130 billion basis functions. [ABSTRACT FROM AUTHOR]

Electronic theory calculations areapplied to the study of theUO molecule and the UO誉. Relativistic effective corepotentials are used along with the accompanying valence spin–orbitoperators. Polarized double-ς and triple-ς basis setsare used. Molecular orbitals are obtained from state-averaged multiconfigurationself-consistent field calculations and then used in multireferencespin–orbit configuration interaction calculations with a numberof millions of terms. The ground state of UO has open shells of 5f37s1, angular momentum Ω = 4, and a spin–orbit-inducedavoided crossing near the equilibrium internuclear distance. ManyUO excited states are studied with rotational constants, intensities,and experimental comparisons. The ground state of UOof 5f3nature with Ω = 9/2. Many UO笗⊵states are also studied. The open-shell nature of both UO and UO闦 to many low-lying excited states. [ABSTRACT FROM AUTHOR]

The electronic absorption spectrumof 9,9-dimethyl-2,7-dinitrofluoreneradical anion in HMPA displays both a NIR intervalence charge transferand a visible excited state mixed valence transition. These transitionscontain a similar vibronic progression resulting from molecular orbitalsthat are common to both transitions. Vibrational frequency and intensitydata are acquired from the resonance Raman spectrum and used to calculatea best fit for the absorption spectrum. The normal coordinate distortionsare analyzed in terms of the electronic changes for both transitionsto explain their similarity. The Raman scattering intensity decreasesat lower excitation wavelength as a result of Raman de-enhancementcaused by interference between neighboring excited states. [ABSTRACT FROM AUTHOR]

A combinationof ultrafast transient electronic absorption spectroscopy(TEAS) and transient vibrational absorption spectroscopy (TVAS) isused to investigate whether photoinduced N–H bond fission,mediated by a dissociative 1πσ* state, is activein aqueous adenine (Ade) at 266 and 220 nm. In order to isolate UV/visibleand IR spectral signatures of the adeninyl radical (Ade[-H]), formedas a result of N–H bond fission, TEAS and TVAS are performedon Ade in D2O under basic conditions (pD = 12.5), whichforms Ade[-H]−anions via deprotonation at the N7or N9 sites of Ade’s 7H and 9H tautomers. At 220 nm we observeone-photon detachment of an electron from Ade[-H]−, which generates solvated electrons (eaq–) together with Ade[-H] radicals,with clear signatures in both TEAS and TVAS. Additional wavelengthdependent TEAS measurements between 240–260 nm identify a thresholdof 4.9 ± 0.1 eV (∼250 nm) for this photodetachment processin D2O. Analogous TEAS experiments on aqueous Ade at pD= 7.4 generate a similar photoproduct signal together with eaq–afterexcitation at 266 and 220 nm. These eaq–are born from ionization ofAde, together with Ade+cations, which are indistinguishablefrom Ade[-H] radicals in TEAS. Ade+and Ade[-H] are foundto have different signatures in TVAS and we verify that the pD = 7.4photoproduct signal observed in TEAS following 220 nm excitation issolely due to Ade+cations. Based on these observations,we conclude that: (i) N–H bond fission in aqueous Ade is inactiveat wavelengths ≥220 nm; and (ii) if such a channel exists inaqueous solution, its threshold is strongly blue-shifted relativeto the onset of the same process in gas phase 9H-Ade (≤233nm). In addition, we extract excited state lifetimes and vibrationalcooling dynamics for 9H-Ade and Ade[-H]−. In both cases, excited state lifetimes of <500fs are identified, while vibrational cooling occurs within a timeframe of 4–5 ps. In contrast, 7H-Ade is confirmed to have alonger excited state lifetime of ∼5–10 ps through bothTEAS and TVAS. [ABSTRACT FROM AUTHOR]

A detailed mechanistic investigationof the early stages of thePaternò–Büchi reaction following 267 nm excitationof benzaldehyde in cyclohexene has been completed using ultrafast,broadband transient UV–visible and IR absorption spectroscopies.Absorption due to electronically excited triplet state benzaldehydedecays on a 80 ps time scale via reaction with cyclohexene. The growthand subsequent decay of the biradical intermediate produced followingC–O bond formation is followed by transient vibrational spectroscopy.The biradical decays by ring closure to an oxetane or by dissociating,reforming the ground state reactants. Detailed kinetic analysis allowedderivation of quantum yields and rate constants for these competingbiradical decay processes, ϕoxetane= 0.53, ϕdiss= 0.47, koxetane= 0.27 ±0.09 ns–1and kdiss=0.24 ± 0.09 ns–1. This study provides a strikingillustration of the ways in which contemporary ultrafast transientabsorption spectroscopy methods can be used to dissect the mechanismand kinetics of a classic photoreaction. [ABSTRACT FROM AUTHOR]

9,9′-Bifluorenylidene hasbeen proposed as an alternativeand flexible electron acceptor in organic photovoltaic cells. Herewe characterize its excited state properties and photokinetics, combiningultrafast fluorescence and transient IR measurements with quantumchemical calculations. The fluorescence decay is ultrafast (sub-100fs) and remarkably independent of viscosity. This suggests that largescale structure change is not the primary relaxation mode. The ultrafastdecay populates a dark state characterized by distinct vibrationaland electronic spectra. This state decays with a 6 ps time constantto a hot ground state that ultimately populates the initial statewith a 20 ps time constant; these times are also insensitive to solventviscosity. No metastable intermediate structures are resolved in thephotocycle after population of the dark state. The implications ofthese results for the operation of 9,9′-bifluorenylidene asan electron acceptor and as a potential molecular switch are discussed. [ABSTRACT FROM AUTHOR]

Wereport a theoretical study of the structures, energetics, andelectronic spectra of the PtII/RuIImixed-metalcomplex RuPt2(tppz)2Cl2(PF6)4(tppz = 2,3,5,6-tetra(2-pyridyl)pyrazine) in acetonitrile.The hybrid B3LYP density functional theory and its TDDFT methods wereused with a complete basis set (CBS) extrapolation scheme and a conductorpolarizable continuum model (C-PCM) for solvation effects. Resultsshowed that the trinuclear complex has four types of stable conformersand/or enantiomers. They are separated by high barriers owing to therepulsive H/H geometrical constraints in tppz. A strong entropy effectwas found for the dissociation of RuPt2(tppz)2Cl2(PF6)nin acetonitrile. The UV–visibleand emission spectra of the complex were also simulated. They arein good agreement with experiments. In this work we have largely focusedon exploring the origin of anomalous electronic circular dichroism(ECD) spectra of the RuPt2(tppz)2Cl2(PF6)4complex in acetonitrile. As a result,a new mechanism has been proposed together with a clear illustrationby using a physical model. [ABSTRACT FROM AUTHOR]

Resonance-enhancedmultiphoton ionization spectroscopy of supersonicallycooled gas-phase 9-hydroxy-9-fluorene carboxylic acid (9HFCA) is reportedfor its first electronic excited state, S1. The UV–UVhole-burning experiment identifies a single conformer in the molecularbeam, stabilized by an intramolecular hydrogen bond. For this Cssymmetric conformer, twolow frequencies in the S1spectrum are assigned: an in-planerocking mode of the carboxylic acid side chain lies at 58 cm–1, and an in-plane fluorene bending mode appears at 183 cm–1. The corresponding mode frequencies in the cation, 58 and 196 cm–1, are measured by zero electron kinetic energy (ZEKE)spectroscopy upon pumping the S1vibronic states. The adiabaticionization potential is measured to be 64 923 ± 5 cm–1. In addition, a feature established by ZEKE spectroscopyupon pumping the hot band is found at 67 cm–1. Thisis assigned as a hot band of the HO–C9–COOH rockingmode in the neutral ground state. [ABSTRACT FROM AUTHOR]

Recently 1-(phenylethynyl)naphthalene(1-PEN) was suggested tobe the primary dimerization product of phenylpropargyl radicals andtherefore an important polycyclic hydrocarbon in combustion processes.Here we describe a spectroscopic investigation of a genuine 1-PENsample by several complementary techniques, infrared spectroscopy,multiphoton ionization (MPI), and threshold photoelectron spectroscopy.The infrared spectrum recorded in a gas cell confirms that 1-PEN isindeed the previously observed dimerization product of phenylpropargyl.The origin of the transition into the electronically excited S1state lies at 30823 cm–1, as found by MPI.Considerable vibrational activity is observed, and a number of low-wavenumberbands are assigned to a progression in the torsional motion. Valuesof 6 cm–1(S0) and 17 cm–1(S1) were derived for the fundamental of the torsion.In the investigated energy range the excited state lifetimes are inthe nanosecond range. Spectra of the 1-PEN/Ar cluster exhibit a redshift of the electronic origin of 22 cm–1, in goodagreement with other aromatic molecules. A threshold photoelectronspectrum recorded using synchrotron radiation yields an ionizationenergy of 7.58 eV for 1-PEN. An excited electronic state of the cationis found at 7.76 eV, and dissociative photoionization does not setin below 15 eV. [ABSTRACT FROM AUTHOR]

Wereport a combined gas phase and solution phase study of 9-fluorenone.The structure and dynamics of isolated fluorenone in the S3-state were studied by resonant enhanced multiphoton ionization withpicosecond pulses in a free jet of molecules excited between 285 and312 nm. Ionization was performed with a second ps-pulse at 351 nm.The electronic spectrum is structured, and the origin of the C 1B2← X 1A1transitionwas observed at 32 122 cm–1. Several vibrational fundamentals appear in the spectrum.In the gas phase we observe a biexponential decay, which suggestsan internal conversion to the coupled S1/S2-statewithin 10–40 ps. A further decay that is assigned to intersystemcrossing was found to be longer than 500 ps. In addition to the gasphase measurements, we studied the photophysics of 9-fluorenone incyclohexane by femtosecond-time-resolved transient absorption spectroscopyand observed very similar dynamics upon excitation to the S3state: It deactivates within 8–11 ps by internal conversion,followed by intersystem crossing within 120–150 ps, forminga long-lived triplet state. Experiments in acetonitrile, however,showed marked differences. Intersystem crossing is ineffective inpolar solvents because the lowest excited singlest state is of ππ*character and does not interact with the 3ππ*. [ABSTRACT FROM AUTHOR]

Donor–acceptor molecules incorporatingfluoren-9-ylidenemalononitrile acceptor units conjugated to trimethoxystyrene and/ordiarylamine donor units were synthesized, and their electronic spectralproperties and electrochemical behaviors were evaluated by comparisonto those of the analogous fluorenones. Frontier energy level and opticaltransition energy trends are explained based on a quantitative, modulardonor–acceptor interaction model. A connectivity effect onabsorption transition moment strength is also described. [ABSTRACT FROM AUTHOR]

Building upon our recent studies of noncovalent interactions in chlorobenzene and bromobenzene clusters, in this work we focus on interactions of chlorobenzene (PhCl) with a prototypical N atom donor, ammonia (NH3). Thus, we have obtained electronic spectra of PhCl···(NH3)n (n = 1-3) complexes in the region of the PhCl monomer S0 −S¹ (ππ*) transition using resonant 2-photon ionization (R2PI) methods combined with time-of-flight mass analysis. Consistent with previous studies, we find that upon ionization the PhCl···NH3 dimer cation radical reacts primarily via Cl atom loss. A second channel, HCl loss, is identified for the first time in R2PI studies of the 1:1 complex, and a third channel, H atom loss, is identified for the first time. While prior studies have assumed the dominance of a π-type complex, we find that the reactive complex corresponds instead to an in-plane σ-type complex. This is supported by electronic structure calculations using density functional theory and post-Hartree-Fock methods and Franck-Condon analysis. The reactive pathways in this system were extensively characterized computationally, and consistent with results from previous calculations, we find two nearly isoenergetic arenium ions (Wheland intermediates; denoted WH1, WH2), which lie energetically below the initially formed dimer cation radical complex. At the energy of our experiment, intermediate WH1, produced from ipso-addition, is not stable with respect to Cl or HCl loss, and the relative branching between these channels observed in our experiment is well reproduced by microcanonical transition state theory calculations based upon the calculated parameters. Intermediate WH2, where NH3 adds ortho to the halogen, decomposes over a large barrier via H atom loss to form protonated o-chloroaniline. This channel is not open at the (2-photon) energy of our experiments, and it is suggested that photodissociation of a long-lived (i.e., several ns) WH2 intermediate leads to the observed products. [ABSTRACT FROM AUTHOR]

Gas-phase ThS has been produced viathe reaction of laser ablatedTh with H2S. Rotationally resolved electronic spectra wererecorded by laser-induced fluorescence (LIF) over the range 17500–24000cm–1. Resonance-enhanced multiphoton ionizationwas used in conjunction with a time-of-flight mass spectrometer toconfirm the assignments of nine LIF bands to ThS. Using excitationof a ThS band centered at 22118 cm–1, a dispersedfluorescence spectrum revealed a vibrational progression of the X1Σ+ground electronic state and the term energiesof two low-lying excited states (3Δ1and 3Δ2). Two-color photoionization spectroscopywas used to study ThS+. An accurate ionization energy forThS was obtained (54425(3) cm–1); ThS+vibronic term energies upto v= 7 in the X2Σ+groundstate and v= 3 in the 2Δ3/2first excited state were recorded. High-level electronic structurecalculations, with inclusion of the spin–orbit interactionsyielded predictions that were in good agreement with the experimentaldata for ThS and ThS+. The spectroscopic properties ofThS/ThS+are compared with those of the valence isoelectronicpairs ThO/ThO+, HfO/HfO+, and HfS/HfS+. [ABSTRACT FROM AUTHOR]

In J-aggregates of cyanine dyes,closely packed molecules formmesoscopic tubes with nanometer-diameter and micrometer-length. Theirefficient energy transfer pathways make them suitable candidates forartificial light harvesting systems. This great potential calls foran in-depth spectroscopic analysis of the underlying energy deactivationnetwork and coherence dynamics. We use two-dimensional electronicspectroscopy with sub-10 fs laser pulses in combination with two-dimensionaldecay-associated spectra analysis to describe the population flowwithin the aggregate. Based on the analysis of Fourier-transform amplitudemaps, we distinguish between vibrational or vibronic coherence dynamicsas the origin of pronounced oscillations in our two-dimensional electronicspectra. [ABSTRACT FROM AUTHOR]

Theelectronic spectroscopy of cold protonated indole was investigatedexperimentally and theoretically. Two isomers were observed by experiment:The first isomer corresponds to the lowest-energy isomer in the calculations,absorbing at ∼350 nm and protonated on the C3atomof the pyrrole ring. According to our calculations, the absorptionsof the other isomers protonated on carbon atoms (C2, C4, C5, C6, and C7) are inthe visible region. Indeed, the absorption of the second observedisomer starts at 488 nm and was assigned to protonation on the C2carbon of the pyrrole ring. Because good agreement was obtainedbetween the calculated and experimental transitions for the observedisomers, reasonable ab initio transition energies can also be expectedfor the higher-energy isomers protonated on other carbon atoms, whichshould also absorb in the visible region. Protonation on the nitrogenatom leads to a transition that is blue-shifted with respect to thatof the most stable isomer. [ABSTRACT FROM AUTHOR]

Transient infrared absorption spectroscopymonitors condensed-phasephotodissociation dynamics of 30 mM CHBr3and 50 mM CHI3in liquid CCl4. The experiments have picosecondtime resolution and monitor the C–H stretch region of boththe parent polyhalomethanes and their photolytically generated isomers.The C–H stretching transitions of these isomers, in which theemergent halogen atom returns to form a C–X–X bondingmotif, appear about 9 ps after photolysis for iso-CHBr2–Br and in about 46 ps for iso-CHI2–I. These time scales are consistent with,but differ from, the time evolution of the transient electronic absorptionspectra of the same samples, highlighting the subtle differences betweenmonitoring the vibrational and electronic chromophores. The specificityof using vibrational transitions to track condensed-phase reactiondynamics permits reassessment of the transient electronic spectrumof photolysis in neat CHBr3, which has an additional promptfeature near 400 nm. Calculations show that this feature, which arisesfrom a precursor to the isomer, is a charge-transfer transition ofa contact pair between the nascent Br fragment and a nearby CHBr3molecule. Dilution and solvent studies show that transitionis independent of the solvent. The iso-CHBr2–Br transition wavelength, however, shifts over the rangeof 400 to 510 nm depending on the solvent. Time-dependent densityfunctional calculations faithfully reproduce these trends. [ABSTRACT FROM AUTHOR]

2′,7′-Dichloro- and 2′,7′-difluorofluoresceinsare superior alternatives to underivatized fluorescein. Although severalstudies characterizing their condensed-phase photophysical propertieshave been reported, little is known about their intrinsic characteristics.Here, the gas-phase properties of three charge states of each fluoresceinare characterized using a quadrupole ion trap mass spectrometer whichhas been modified for spectroscopy. Electronic action spectra, constructedby monitoring the extent of photodissociation as a function of excitationwavelength, indicate that the gaseous dianions and cations resembletheir solution-phase counterparts. In contrast, a large shift in theelectronic action spectra of the monoanions indicates the presenceof a different tautomer in the gas phase than that present in solution.The gaseous monoanion is deprotonated on the xanthene ring, ratherthan being deprotonated on the pendant group as found in soluion.The dianions and cations do not emit detectable fluorescence in thegas phase. In contrast, the monoanions do fluoresce, but the emissionintensity is low and the spectra are broad. This work illustratesthe effect of halogenation on the intrinsic properties of the dyesand provides useful fundamental understanding that promises to aidthe development more robust fluorescent dyes. [ABSTRACT FROM AUTHOR]

The electronic spectra of Co+(H2O), Co+(HOD), and Co+(D2O) havebeen measuredfrom 13 500 to 18 400 cm–1using photodissociation spectroscopy. Transitionsto four excited electronic states with vibrational and partially resolvedrotational structure are observed. Each electronic transition hasan extended progression in the metal–ligand stretch, v3, and the absolute vibrational quantum numbering is assignedby comparing isotopic shifts between Co+(H216O) and Co+(H218O). For thelow-lying excited electronic states, the first observed transitionis to v3′ = 1. This allows the Co+–(H2O) binding energy to be determined as D0(0 K)(Co+–H2O) = 13730 ±90 cm–1(164.2 ± 1.1 kJ/mol). The photodissociationspectrum shows a well-resolved Kaband structure due to rotation about the Co–O axis.This permits determination of the spin rotation constants ϵaa″= −6 cm–1and ϵaa′= 4cm–1. However, the Karotational structure depends on v3′.These perturbations in the spectrum make the rotational constantsunreliable. From the nuclear spin statistics of the rotational structure,the ground state is assigned as 3B1. The electronictransitions observed are from the Co+(H2O) groundstate, which correlates to the cobalt ion’s 3F,3d8ground state, to excited states which correlate tothe 3F, 3d74s and 3P, 3d8excited states of Co+. These excited states of Co+interact less strongly with water than the ground state.As a result, the excited states are less tightly bound and have longermetal–ligand bonds. Calculations at the CCSD(T)/aug-cc-pVTZlevel also predict that binding to Co+increases the H–O–Hangle in water from 104.1° to 106.8°, as the metal removeselectron density from the oxygen lone pairs. The O–H stretchingfrequencies of the ground electronic state of Co+(H2O) and Co+(HOD) have been measured by combiningIR excitation with visible photodissociation in a double resonanceexperiment. In Co+(H2O) the O–H symmetricstretch is ν1″ = 3609.7 ± 1 cm–1. The antisymmetric stretch is ν5″ = 3679.5± 2 cm–1. These values are 47 and 76 cm–1, respectively, lower than those in bare H2O. In Co+(HOD) the O–H stretch is observed at 3650cm–1, a red shift of 57 cm–1relativeto bare HOD. [ABSTRACT FROM AUTHOR]

The absorption and fluorescence spectra of two analoguesof 10-hydroxybenzo[h]quinoline (10-HBQ), namely,1-hydroxy-7-methylbenzo[c]acridine (HMBA) and 4-hydroxybenzo[c]phenanthridine(HBPA), were studied in n-alkane matrices at 5 K.Considerable energy separation between the onsets of the spectra andbroadening of the bands wasan indication that intramolecular proton transfer (ESIPT) takes placeat such a low temperature. DFT and ab initio methods were used tocalculate the electronic transition energies and oscillator strengthsand the vibronic structure of the electronic spectra. Shortcomingsin our knowledge of the shape of the potential energy surface forESIPT systems are highlighted in the context of the discussion ofthe shape of the electronic spectra. The ?-expansion of the10-HBQ chromophore achieved by adding a benzene moiety at variouspositions adjacent to the pyridine ring led to compounds possessingdiverse photophysical properties, ranging from the non-ESIPT stronglyfluorescent molecule of 10-hydroxy-1-azaperylene to weakly emitting(or nonemitting) molecules, where ESIPT occurs very efficiently. [ABSTRACT FROM AUTHOR]

The potential energy curves and spectroscopic constantsof theground and excited states of the RbAr van der Waals system have beendetermined using a one-electron pseudopotential approach. This techniqueis used to replace the effect of the Rb+core and the electron–Arinteractions by effective potentials. The core–core interactionfor Rb+Ar was incorporated using the accurate CCSD(T) potentialof Hickling et al. [Hickling,H. L.; Viehland, L. A.; Shepherd, D. T.; Soldán, P.; Lee, E.P. F.; Wright, T. G. Phys. Chem. Chem. Phys.2004, 6, 4233−4239]. This model reduces the number of activeelectrons of the RbAr van der Waals systems to just the single valenceelectron, permitting the use of very large basis sets for the Rb andAr atoms. Using this approach, the potential energy curves of theground and excited states dissociating into Rb(5s, 5p, 4d, 6s, 6p,6d, and 7s) + Ar are calculated at the SCF level. Spin–orbitinteraction was also considered within a semiempirical scheme forthe states dissociating into Rb(5p) and Rb(6p). Spectroscopic constantsare derived and compared with the available theoretical and experimentaldata. Such comparisons for RbAr show very good agreement for the groundand the first excited states. Furthermore, we have predicted the B2Σ+1/2← X2Σ+, A2Π1/2← X2Σ+, A2Π3/2←X2Σ+, A2Π3/2← X2Σ+, 52Σ+← X2Σ+, 32Π1/2← X2Σ+, and 32Π3/2← X2Σ+absorptionspectra. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations have been employed forthe investigationof the lowest excited electronic states of lutein, with particularreference to its function within light harvesting antenna complexesof higher plants. Through comparative analysis obtained by using differentmethods based on gas-phase calculations of the spectra, it was determinedthat variations in the lengths of the long C–C valence bondsand the dihedral angles of the polyene chain are the dominant factorsin determining the spectral properties of Lut 1 and Lut 2 correspondingto the deformed lutein molecules taken from crystallographic dataof the major pigment–protein complex of photosystem II. ByMNDO-CAS-CI method, it was determined that the two singlet Bustates of lutein (nominally 1Bu–* and1Bu+) arise as a result of mixing of the canonical1Bu–and 1Bu+statesof the all-transpolyene due to the presence of theending rings in lutein. The 1Bu–* stateof lutein is optically allowed, while the 1Bu–of a pure all-transpolyene chain is opticallyforbidden. As demonstrated, the Bustates are much moresensitive to minor distortions of the conjugated chain due to mixingof the canonical states, resulting in states of poorly defined particle–holesymmetry. Conversely, the Agstates are relatively robustwith respect to geometric distortion, and their respective inversionand particle–hole symmetries remain relatively well-defined. [ABSTRACT FROM AUTHOR]

The electronic transition spectrum of IrO in the spectralregion between 448 and 650 nm has been recorded and analyzed usinglaser vaporization/reaction free jet expansion and laser induced fluorescencespectroscopy. The IrO molecule was produced by reacting laser-ablatediridium atoms with N2O seeded in argon. Five electronictransition systems, namely, the [17.6]2.5 – X2Δ5/2, [17.8]2.5 – X2Δ5/2,[21.5]2.5 – X2Δ5/2, [22.0]2.5 –X2Δ5/2, and [21.9]3.5 – Ω= 3.5 systems were identified. Transition lines of both the 191IrO and 193IrO isotopes were observed and analyzed. IrOwas determined to have a X2Δ5/2groundstate. A least squares fit of the measured rotational lines yieldedmolecular constants for the ground and low-lying electronic states.A molecular orbital energy level diagram has been used to help withthe assignment of the observed electronic states. [ABSTRACT FROM AUTHOR]

A detailed study of the structure, infrared, and electronicspectraof the mixed-metal group 7 carbonyls MnTc(CO)10, MnRe(CO)10, and TcRe(CO)10is presented using density functionaltheory, and time-dependent density functional theory, with a varietyof modern density functionals. Long-range corrected density functionalsare needed to accurately model the transitions in such complexes,and through calibration with data for known bimetallic carbonyls,DFT and TD-DFT can be used to predict the behavior of their as yetelusive counterparts. [ABSTRACT FROM AUTHOR]

Quantitative ab initio calculations are presented forthe ultraviolet–visiblepeaks of cycl[3.2.2]azine and its mono- and dibenzannulated polycycliccompounds at the multistate CASPT2 (MS-CASPT2) level of theory, with11 nm deviation from the experimental S0→ S1absorption. The electrophilic substitution reactions of cycl[3.2.2]azine,benzo[a]/[g]annulated cycl[3.2.2]azines,and 6-dimethylamino[2.2.3]cyclazine-1-carboxylates with 3-cyano-4-methylthiomaleimidegave the corresponding functionalized cycl[3.2.2]azine derivatives,which exhibited the absorption maxima around 510–630 nm. Thefirst intense peaks were investigated by means of time-dependent densityfunctional theory (TD-DFT). These peaks were systematically underevaluatedby ∼50 nm, within the acceptable accuracies of TD-DFT. Furthermore,we calculated vibronic coupling constants of the electronic excitedstates of cycl[3.2.2]azine and simulated absorption spectra both invacuo and in ethanol. The solvent effect is found to enhance oscillatorstrengths and vibronic couplings. This is because the solvent effectgives rise to changes in the electron density difference on the phenylring, and in turn, the intensified overlap between the electron densitydifference and the potential derivative in the phenyl ring leads toenhanced vibronic couplings in ethanol. [ABSTRACT FROM AUTHOR]

The photoreaction mechanisms of 2-naphthol and carbazolein low-temperatureargon matrices have been investigated by infrared and electronic absorptionspectroscopy with aids of density-functional-theory (DFT) and time-dependentDFT (TD-DFT) calculations. When the matrix samples were irradiatedupon UV light, 2-naphthoxyl and N-carbazolyl radicals were producedby the elimination of the H atom in the O–H group of 2-naphtholand in the N–H group of carbazole, respectively. The observedIR and electronic absorption spectra of the radicals were reproducedsatisfactorily by the quantum chemical calculations. To understanda role of the radicals in the excited-state proton transfer (ESPT),the fluorescence and excitation spectra of 2-naphthol and carbazolewere measured in aqueous solution at room temperature as well as inthe low-temperature argon matrices. It was found that the intensityof the fluorescence emitted from carbazole anion in aqueous solutiondecreased when oxygen gas was blown into the solution. [ABSTRACT FROM AUTHOR]

The structures of 17β-estradiol (estradiol) andits 1:1 clusterwith water have been investigated in supersonic jets. The S1–S0electronic spectrum of estradiol monomer showsfour strong sharp bands in the 35050–35200 cm–1region. Ultraviolet–ultraviolet hole-burning (UV–UVHB) and infrared-ultraviolet double-resonance (IR-UV DR) spectra ofthese bands indicate that they are due to four different conformersof estradiol originating from the different orientation of the OHgroups in the A- and D-rings. Theaddition of water vapor to the sample gas generates four new bandsin the 34700–34800 cm–1region, which areassigned to the estradiol–H2O 1:1 cluster with the A-ring (phenyl ring) OH acting as a hydrogen(H)-bond donor.In addition, we found very weak bands near the origin bands of bareestradiol upon the addition of water vapor. These bands are assignedto the isomers of estradiol–H2O 1:1 cluster havingan H-bond at the D-ring OH. We determine the conformationof bare estradiol and the structures of its monohydrated clusterswith the aid of density functional theory calculation and discussthe relationship between the stability of hydrated clusters and theconformation of estradiol. [ABSTRACT FROM AUTHOR]

The electronic spectra were measured and the unimoleculardecay kinetics of the isomeric forms (cis and trans) of 4-methoxyphenylnitrosooxide in acetonitrile, benzene, and hexane was studied using flashphotolysis. The cis form absorbed in a shorter wavelength region andwas more labile than the trans form. The difference between the reactivityof the two species increased on going from hexane to acetonitrile.The temperature dependences of reaction rate constants were studiedfor both isomeric forms. The analysis of products of flash photolysisof 4-methoxyphenyl azide in the presence of oxygen allowed for understandingthe mechanism of thermal decay of nitroso oxides. It was shown thatthe trans nitroso oxide is converted into cis nitroso oxide. The latterundergoes an unusual ring cleavage reaction to form 4-methoxy-6-oxohexa-2,4-dienenitrileN-oxide derivative. We conclude that the nitro- and nitrosobenzenes,which are the main products of the steady-state photolysis of aromaticazides in the presence of oxygen, are formed by the photochemicaltransformation of the nitroso oxides. [ABSTRACT FROM AUTHOR]

The electronic origin bands A and B of 5-hydroxyindolewere measuredusing rotationally resolved electronic spectroscopy. From comparisonof the experimental rotational constants to the results of ab initiocalculated structures, we could make the assignment of band A beingdue to the synconformer and of band B being dueto the anticonformer. These conformers, which differin the orientation of the hydroxy group with respect to the rest ofthe molecule, have considerably different S1state lifetimes. The most probable explanation for this surprising finding isa different conical intersection of the ππ* states ofboth conformers with the repulsive πσ* state. [ABSTRACT FROM AUTHOR]

Four-component relativistic time-dependent density functionaltheory(TD-DFT) is used to study charge-transfer (CT) excitation energiesof the uranyl molecule as well as the uranyl tetrachloride complex.Adiabatic excitation energies and vibrational frequencies of the excitedstates are calculated for the lower energy range of the spectrum.The results for TD-DFT with the CAM-B3LYP exchange–correlationfunctional for the [UO2Cl4]2–system are in good agreement with the experimentally observed spectrumof this species and agree also rather well with other theoreticaldata. Use of the global hybrid B3LYP gives qualitatively correct results,while use of the BLYP functional yields results that are qualitativelywrong due to the too low CT states calculated with this functional.The applicability of the overlap diagnostic of Peach et al. (J. Chem. Phys.2008, 128,044118) to identify such CT excitations is investigated for a widerange of vertical transitions using results obtained with three differentapproximate exchange–correlation functionals: BLYP, B3LYP,and CAM-B3LYP. [ABSTRACT FROM AUTHOR]

A series of europium cryptates are studied, using semiempiricalmethods to predict electronic and spectroscopic properties. The resultsare compared with theoretical (DFT) and experimental results publishedby Guillaumont and co-workers (ChemPhysChem2007, 8, 480). Triplet energies calculatedby semiempirical methods have errors similar to those obtained byTD-DFT methodology but hundreds of times faster. Moreover, the semiempiricalresults not only reproduce well the experimental values but also helpexplain the low values of quantum efficiency observed for these complexes. [ABSTRACT FROM AUTHOR]

Electronic spectra of the gas-phase isoquinoline+-Arand quinoline+-Ar complexes are recorded using photodissociationspectroscopy by monitoring the Ar loss channel. The D3←D0and D4←D0band origins forisoquinoline+-Ar are observed at 15245 ± 15 cm–1and 21960 ± 15 cm–1, respectively,whereas for quinoline+-Ar they appear at 16050 ± 15cm–1and 21955 ± 15 cm–1,respectively. Strong vibronic progressions for the D3←D0band systems ofboth isoquinoline+-Ar and quinoline+-Ar aremodeled and assigned in terms of ring deformation and carbon–carbonstretch vibrational modes using time-dependent density functionaltheory calculations in conjunction with Franck–Condon simulations.The properties of the isoquinoline+and quinoline+molecules are compared with those of the isoelectronic naphthalene+molecule. The existence of strong progressions in the visiblespectra of isoquinoline+-Ar and quinoline+-Arsuggests that the corresponding isoquinoline+and quinoline+molecular cations are unlikely to be responsible for diffuseinterstellar bands. [ABSTRACT FROM AUTHOR]