Franck-Condon Analyses Research Articles

Relating reorganization energies, exciton diffusion length and non-radiative recombination to the room temperature UV-vis absorption spectra of NF-SMA.

Understanding excited-state reorganization energies, exciton diffusion lengths and non-radiative (NR) recombination, and the overall optoelectronic responses of nonfullerene small molecule acceptors (NF-SMAs) is important in order to rationally design new materials with controlled properties. While the effects of structural modifications on the optical gaps and electron affinities of NF-SMAs have been studied extensively, analyses of their absorption spectra that carefully characterize electronic and vibrational contributions that allow comparisons of reorganization energies and their implications for exciton diffusion lengths and NR recombination have yet to be reported. Here, we study the room temperature absorption spectra of three structural classes of NF-SMAs in dilute solutions through multiparameter Franck Condon (MFC) analyses and density functional theory (DFT) calculations. We show that the absorption spectra of these NF-SMAs can be categorized based on molecular structure-spectra correlation. The absorption spectra of curved, Y6-like structures can be described using an MFC model with two electronic transitions and two effective vibrational modes. The results of MFC/DFT analyses reveal that Y6 exhibits the smallest intra-molecular reorganization energy among the materials studied. Linear ITIC-like molecular structures reveal larger reorganization energies and reduced conformational uniformity compared to Y6. Meanwhile structures such as IDTBR and IEICO, which have an extra π-conjugated moiety between the donor and acceptor moieties, have large excited-state reorganization energies and low degrees of conformational uniformity. Since the intra-molecular reorganization energy is correlated with exciton diffusion length and nonradiative voltage losses (ΔVnr), our results highlight the power of RT absorption spectroscopy and DFT calculations as simple tools to designing improved OSCs materials with small reorganization energies, small ΔVnr, large exciton diffusion length and low energetic disorder (due to a strongly dominant conformation).

Experimentally Calibrated Analysis of the Electronic Structure of CuO+: Implications for Reactivity

AbstractThe CuO+ core is a central motif of reactive intermediates in copper‐catalysed oxidations occurring in nature. The high reactivity of CuO+ stems from a weak bonding between the atoms, which cannot be described by a simple classical model. To obtain the correct picture, we have investigated the acetonitrile‐ligated CuO+ ion using neon‐tagging photodissociation spectroscopy at 5 K. The spectra feature complex vibronic absorption progressions in NIR and visible regions. Employing Franck–Condon analyses, we derived low‐lying triplet potential energy surfaces that were further correlated with multireference calculations. This provided insight into the ground and low‐lying excited electronic states of the CuO+ unit and elucidated how these states are perturbed by the change in ligation. Thus, we show that the bare CuO+ ion has prevailingly a copper(I)‐biradical oxygen character. Increasing the number of ligands coordinated to copper changes the CuO+ character towards the copper(II)‐oxyl radical structure.

Experimentally Calibrated Analysis of the Electronic Structure of CuO+ : Implications for Reactivity.

The CuO+ core is a central motif of reactive intermediates in copper-catalysed oxidations occurring in nature. The high reactivity of CuO+ stems from a weak bonding between the atoms, which cannot be described by a simple classical model. To obtain the correct picture, we have investigated the acetonitrile-ligated CuO+ ion using neon-tagging photodissociation spectroscopy at 5 K. The spectra feature complex vibronic absorption progressions in NIR and visible regions. Employing Franck-Condon analyses, we derived low-lying triplet potential energy surfaces that were further correlated with multireference calculations. This provided insight into the ground and low-lying excited electronic states of the CuO+ unit and elucidated how these states are perturbed by the change in ligation. Thus, we show that the bare CuO+ ion has prevailingly a copper(I)-biradical oxygen character. Increasing the number of ligands coordinated to copper changes the CuO+ character towards the copper(II)-oxyl radical structure.

Ground and low-lying excited states of phenoxy, 1-naphthoxy, and 2-naphthoxy radicals via anion photoelectron spectroscopy.

We present the slow electron velocity map imaging spectroscopy of cryogenically cooled phenoxide, 1-naphthoxide, and 2-naphthoxide anions. The results allow us to examine the ground state and the lowest energy excited state in the corresponding neutral radicals. Care was taken to minimize autodetachment signals in the photoelectron spectra, allowing for more straightforward comparisons with Franck-Condon analyses. The ground states of these three aromatic oxide radicals all have the unpaired electron residing in a π orbital delocalized throughout the molecule. The electron affinity of 1-naphthoxy is measured to be 2.290(2) eV, while that of 2-naphthoxy is measured to be 2.404(2) eV, both of which are higher than that of the smaller phenoxy molecule at 2.253(1) eV. The first excited states have the unpaired electron residing in a more localized σ orbital, yielding measured term energies for the state of 1.237(2) eV in 1-naphthoxy and 1.068(1) eV in 2-naphthoxy, while that of phenoxy is lower at 0.952(1) eV. The calculated Franck-Condon spectra generally showed good agreement with the experimental spectra, yielding assignments of the more active vibrations in each electronic state. Significant autodetachment signals arising from dipole bound states near the ground states of all three radicals were observed in our efforts to avoid them, and comparably less autodetachment signals were observed near the excited states. Besides this type of non-Franck-Condon intensities in the photoelectron spectra, we also observed minor features arising due to vibronic coupling in the ground states of all three radicals.

A combined theoretical and experimental study of the valence and Rydberg states of iodopentafluorobenzene.

A new ultraviolet (UV) and vacuum ultraviolet (VUV) spectrum for iodopentafluorobenzene (C6F5I) using synchrotron radiation is reported. The measurements have been combined with those from a recent high-resolution photoelectron spectroscopic study. A major theoretical study, which includes both Franck-Condon (FC) and Herzberg-Teller (HT) analyses, leads to conclusions, which are compatible with both experimental studies. Our observation that the VUV multiplet at 7.926 eV in the VUV spectrum is a Rydberg state rather than a valence state leads to a fundamental reassignment of the VUV Rydberg spectrum over previous studies and removes an anomaly where some previously assigned Rydberg states were to optically forbidden states. Adiabatic excitation energies (AEEs) were determined from equations-of-motion coupled cluster with singles and doubles excitation; these were combined with time dependent density functional theoretical methods. Frequencies from these two methods are very similar, and this enabled the evaluation of both FC and HT contributions in the lower valence states. Multi-reference multi-root configuration interaction gave a satisfactory account of the principal UV+VUV spectral profile of C6F5I, with vertical band positions and intensities. The UV spectral onset consists of two very weak transitions assigned to 11B1 (πσ*) and 11B2 (σσ*) symmetries. The lowest unoccupied molecular orbital of a σ*(a1) symmetry has a significant C-I* antibonding character. This results in considerable lengthening of the C-I bond for both these excited states. The vibrational intensity of the lowest 11B1 state is dominated by HT contributions; the 11B2 state contains both HT and FC contributions; the third band, which contains three states, two ππ*(11A1, 21B2) and one πσ*(21B1), is dominated by FC contributions in the 1A1 state. In this 1A1 state, and the spectrally dominant bands near 6.7 (1A1) and 7.3 eV (1A1 + 1B2), the C-I bond length is in the normal range, and FC components dominate.

Effect of alkoxy side chains on intra and interchain exciton coupling in PPE-PPV copolymers solution

The effects of alkoxy side chains on the optical and morphological properties of five poly (p-phenylene-ethylene)-alt-poly (p-phenylene-vinylene)s (PPE-PPVs) solutions are investigated. By steady-state and time-resolved photoluminescence spectroscopy combined with Franck-Condon analyses, we show that the introduction of symmetrical side chains onto the PPE-PPV backbone increases the π–π stacking between the polymer chains leading to interchain interactions hence H-aggregate domains. Total dissymmetrical side chains lead to J-aggregate domains through intrachain interactions. On the other hand partial dissymmetrical side chain configurations lead to H and HJ-aggregate domains.

Combined theoretical and experimental study of the valence, Rydberg, and ionic states of chlorobenzene.

New photoelectron (PE) and ultra violet (UV) and vacuum UV (VUV) spectra have been obtained for chlorobenzene by synchrotron study with higher sensitivity and resolution than previous work and are subjected to detailed analysis. In addition, we report on the mass-resolved (2 + 1) resonance enhanced multiphoton ionization (REMPI) spectra of a jet-cooled sample. Both the VUV and REMPI spectra have enabled identification of a considerable number of Rydberg states for the first time. The use of ab initio calculations, which include both multi-reference multi-root doubles and singles configuration interaction (MRD-CI) and time dependent density functional theoretical (TDDFT) methods, has led to major advances in interpretation of the vibrational structure of the ionic and electronically excited states. Franck-Condon (FC) analyses of the PE spectra, including both hot and cold bands, indicate much more complex envelopes than previously thought. The sequence of ionic states can be best interpreted by our multi-configuration self-consistent field computations and also by comparison of the calculated vibrational structure of the B and C ionic states with experiment; these conclusions suggest that the leading sequence is the same as that of iodobenzene and bromobenzene, namely: X(2)B1(3b1 (-1)) < A(2)A2(1a2 (-1)) < B(2)B2(6b2 (-1)) < C(2)B1(2b1 (-1)). The absorption onset near 4.6 eV has been investigated using MRD-CI and TDDFT calculations; the principal component of this band is (1)B2 and an interpretation based on the superposition of FC and Herzberg-Teller contributions has been performed. The other low-lying absorption band near 5.8 eV is dominated by a (1)A1 state, but an underlying weak (1)B1 state (πσ(∗)) is also found. The strongest band in the VUV spectrum near 6.7 eV is poorly resolved and is analyzed in terms of two ππ(∗) states of (1)A1 (higher oscillator strength) and (1)B2 (lower oscillator strength) symmetries, respectively. The calculated vertical excitation energies of these two states are critically dependent upon the presence of Rydberg functions in the basis set, since both manifolds are strongly perturbed by the Rydberg states in this energy range. A number of equilibrium structures of the ionic and singlet excited states show that the molecular structure is less subject to variation than corresponding studies for iodobenzene and bromobenzene.

Heteroleptic [Os(H)(CO)(N∧N)(tpp)2]+ and [Os(Cl)(CO)(N∧N)(tpp)2]+ complexes - comparative studies of their luminescence properties.

Two series of cationic heteroleptic osmium(ii) complexes with a coordinated CO molecule, a chloride Cl- or hydride H- anion, two monodentate triphenylphosphine (tpp) ligands and one bidentate α-dimine (N∧N) ligand were prepared from an OsCl2(CO)2(tpp)2 precursor. The investigated complexes, available in the form of PF6- salts, have been identified by means of FT-IR, 1H and 31P NMR spectroscopy and X-ray diffraction studies. Their photophysical properties have been investigated in dichloromethane solutions at room temperature and 1 : 1 ethanol-methanol matrices at 77 K. The investigated complexes exhibit metal to ligand charge-transfer (MLCT) phosphorescence with the emission characteristics distinctly affected by the nature of coordinated α-diimine N∧N and Cl- or H- ligands. Franck-Condon emission spectral band shape analyses and DFT/TD-DFT calculations have been applied to obtain more detailed insight into the nature of emissive 3*[Os(H)(CO)(N∧N)(tpp)2]+ and 3*[Os(Cl)(CO)(N∧N)(tpp)2]+ species.

Interpretation of the photoelectron, ultraviolet, and vacuum ultraviolet photoabsorption spectra of bromobenzene by ab initio configuration interaction and DFT computations.

New photoelectron, ultraviolet (UV), and vacuum UV (VUV) spectra have been obtained for bromobenzene by synchrotron study with higher sensitivity and resolution than previous work. This, together with use of ab initio calculations with both configuration interaction and time dependent density functional theoretical methods, has led to major advances in interpretation. The VUV spectrum has led to identification of a considerable number of Rydberg states for the first time. The Franck-Condon (FC) analyses including both hot and cold bands lead to identification of the vibrational structure of both ionic and electronically excited states including two Rydberg states. The UV onset has been interpreted in some detail, and an interpretation based on the superposition of FC and Herzberg-Teller contributions has been performed. In a similar way, the 6 eV absorption band which is poorly resolved is analysed in terms of the presence of two ππ* states of (1)A1 (higher oscillator strength) and (1)B2 (lower oscillator strength) symmetries, respectively. The detailed analysis of the vibrational structure of the 2(2)B1 ionic state is particularly challenging, and the best interpretation is based on equation-of-motion-coupled cluster with singles and doubles computations. A number of equilibrium structures of the ionic and singlet excited states show that the molecular structure is less subject to variation than corresponding studies for iodobenzene. The equilibrium structures of the 3b13s and 6b23s (valence shell numbering) Rydberg states have been obtained and compared with the corresponding ionic limit structures.

Spectroscopic Signature of Two Distinct H-Aggregate Species in Poly(3-hexylthiophene)

In an endeavor to correlate the optoelectronic properties of π-conjugated polymers with their structural properties, we investigated the aggregation of P3HT in THF solution within a temperature range from 300 to 5 K. By detailed steady-state, site-selective, and time-resolved fluorescence spectroscopy combined with Franck–Condon analyses, we show that below a certain transition temperature (265 K) aggregates are formed that prevail in different polymorphs. At 5 K, we can spectroscopically identify two H-type aggregates with planar polymer backbones yet different degree of order regarding their side chains. Upon heating, the H-character of the aggregates becomes gradually eroded, until just below the transition temperature the prevailing “aggregate” structure is that of still phase-separated, yet disordered main and side chains. These conclusions are derived by analyzing the vibrational structure of the spectra and from comparing the solution spectra with those obtained from thin films that were cooled slo...

Varying the electronic structure of surface-bound ruthenium(II) polypyridyl complexes.

In the design of light-harvesting chromophores for use in dye-sensitized photoelectrosynthesis cells (DSPECs), surface binding to metal oxides in aqueous solutions is often inhibited by synthetic difficulties. We report here a systematic synthesis approach for preparing a family of Ru(II) polypyridyl complexes of the type [Ru(4,4'-R2-bpy)2(4,4'-(PO3H2)2-bpy)](2+) (4,4'(PO3H2)2-bpy = [2,2'-bipyridine]-4,4'-diylbis(phosphonic acid); 4,4'-R2-bpy = 4,4'-R2-2,2'-bipyridine; and R = OCH3, CH3, H, or Br). In this series, the nature of the 4,4'-R2-bpy ligand is modified through the incorporation of electron-donating (R = OCH3 or CH3) or electron-withdrawing (R = Br) functionalities to tune redox potentials and excited-state energies. Electrochemical measurements show that the ground-state potentials, E(o')(Ru(3+/2+)), vary from 1.08 to 1.45 V (vs NHE) when the complexes are immobilized on TiO2 electrodes in aqueous HClO4 (0.1 M) as a result of increased Ru dπ-π* back-bonding caused by the lowering of the π* orbitals on the 4,4'-R2-bpy ligand. The same ligand variations cause a negligible shift in the metal-to-ligand charge-transfer absorption energies. Emission energies decrease from λmax = 644 to 708 nm across the series. Excited-state redox potentials are derived from single-mode Franck-Condon analyses of room-temperature emission spectra and are discussed in the context of DSPEC applications.

Mn-activated Na2SiF6 red and yellowish-green phosphors: A comparative study

Mn4+- and Mn2+-activated red and yellowish-green phosphors have been synthesized by the wet chemical etching of Si wafers in aqueous HF/NaMnO4 · H2O and HF/Na2Cr2O7 · 2H2O/Mn solutions, respectively. X-ray diffraction patterns suggest that the synthesized powders are Na2SiF6:Mn4+ and Na2SiF6:Mn2+ with a trigonal structure (space group = D32-P321). Photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and diffuse reflectance measurements were carried out to investigate the optical properties of the phosphors. Franck-Condon analyses of the PL and PLE spectra were performed to determine the zero-phonon energies of the Mn4+- and Mn2+-related transitions in Na2SiF6. Temperature-dependent PL and luminescence decay time measurements were performed from 20 to 300 K, and the obtained results are explained on the basis of the energy level diagram of the 3d3 (Mn4+) and 3d5(Mn2+) electrons in Na2SiF6, taking into account the thermal quenching effect. Electron spin resonance measurements were also performed. This is the first reported synthesis of a yellowish-green phosphor using Na2XF6 (X = a tetravalent metallic ion) as the host crystal.

A combined ab initio and Franck–Condon simulation study of the photodetachment spectrum of the [formula omitted] anion

A general analytical expression for the calculation of the two-dimensional four-mode Franck–Condon overlap integrals was presented and applied to scrutinize the photoelectron spectroscopy of ClO 2 - . Geometry optimization and harmonic vibrational frequency calculations have been performed on the X ∼ 2B 1 state of ClO 2 and X ∼ 1A 1 state of ClO 2 - by using the density functional theory (B2PLYP functional) and the coupled cluster singles and doubles with perturbative triples [CCSD(T)] methods with various basis sets up to aug-cc-pVQZ. The adiabatic electron affinity of ClO 2 was computed by using the CCSD(T) method extrapolated to the complete basis set limit with aug-cc-pVXZ (X = D, T, Q). Franck–Condon analyses and spectral simulation were carried out on the ClO 2( X ∼ 2B 1)–( ClO 2 - X ∼ 1A 1) photodetachment process. The simulated photoelectron spectrum of ClO 2 - are in accord with the experiment. While the Duschinsky effect plays a minor role and can be neglected. In addition, the equilibrium geometry parameters, R(Cl–O) = 1.572 ± 0.005 Å and ∠ (O–Cl–O) = 112.5 ± 0.5°, of the X ∼ 1A 1 state of ClO 2 - , are obtained by employing an iterative Franck–Condon analysis procedure in the spectral simulations.

A general analytical expression for the two-dimensional Franck–Condon integral and simulation of the photoelectron spectra of nitrogen dioxide

On the basis of the harmonic oscillator approximation, the two-dimensional four-mode Franck–Condon vibrational overlap integral under mode-mixing effects has been reduced to a product expression of one-dimensional Gaussian integrals with the aid of expanding Hermite polynomials. A more general analytical expression for the calculation of the two-dimensional four-mode Franck–Condon overlap integrals was derived by directly calculating the Gaussian integrals. This analytical expression was applied to investigate the photoelectron spectra of considering mode-mixing and hot band effects. Geometry optimizations and harmonic vibrational frequency calculations were performed on the 2A1 state of NO2 and the 1A1 state of . Franck–Condon analyses and spectral simulations were carried out on the NO2( 2A1)–( 1A1) photodetachment processes. The spectral simulations of vibrational structures based on the computed Franck–Condon factors are in excellent agreement with the observed spectra. In addition, the equilibrium geometric parameters of the 1A1 state of were obtained in the spectral simulations: bond length R(ON) = 1.248 ± 0.005 Å and bond angle ∠ (ONO) = 116.8 ± 0.5°.

Vibrationally resolved photoelectron imaging of gold hydride cluster anions: AuH− and Au2H−

Photoelectron spectra and angular distributions in photodetachment of gold hydride anions AuH(-) and Au(2)H(-) have been obtained using photoelectron velocity-map imaging. Both the images exhibit vibrationally resolved ground state transitions. The adiabatic electron affinities of AuH and Au(2)H are measured to be 0.758(20) and 3.437(3) eV, respectively. Franck-Condon analyses of the AuH spectra determined that the equilibrium bond length of the ground state of AuH(-) is 1.597(6) A. The photoelectron images of Au(2)H(-) show a vibrational progression of 148(4) cm(-1) assigned to the Au-Au stretching mode at the ground state. Ab initio calculation results are in excellent agreement with the experimental results. For the ground state of Au(2)H, a new bent Au-Au-H structure with the angle of 131 degrees is suggested. Moreover, energy-dependent photoelectron anisotropy parameters are also reported and discussed.

Triplet energy transfer in conjugated polymers. III. An experimental assessment regarding the influence of disorder on polaronic transport

It is a general notion that, in organic semiconductors, the transport of electronic excitations, such as neutral excitons of singlet or triplet type and charge carriers, is controlled by both, polaron and disorder effects. For compounds with low energetic disorder triplet exciton diffusion can be described in the framework of Marcus-theory [see Sudha Devi et al.,Phys. Rev. B 78, 045210 (2008)], and a theoretical model for diffusion in more disordered compounds has been developed [see Fishchuk et al., Phys. Rev. B 78, 045211 (2008)]. Here we experimentally demonstrate that such a modified Marcus-type model is suitable to describe triplet exciton transport in commonly used poly($p$-phenylene)-type polymers and oligomers. In particular, we provide a quantitative spectroscopic assessment of the polaronic and the disorder contribution to triplet exciton transport as a function of conjugation length. Franck-Condon analyses of the phosphorescence spectra and temperature-dependent triplet diffusion combined with analytic transport theory demonstrate that, in contrast to charge carriers, Marcus-type jump rates with dominantly polaronic activation energies control the motion of triplet excitons above a transition temperature.

Calculation of Franck–Condon factors and simulation of photoelectron spectroscopy of D 2CO: Including Duschinsky effects

Calculations of Franck–Condon factors are crucial for interpreting vibronic spectra of molecules and studying nonradiative processes. On the base of the closed form expression of the Franck–Condon integrals between arbitrary multidimensional harmonic oscillators under the Duschinsky mixing effects, a more general algebraic expression for the calculation of the three-dimensional four-mode Franck–Condon factors was derived straightforwardly and applied to study the photoelectron spectrum of D 2 CO + ( B ∼ 2 A 1 ) . Geometry optimization and harmonic vibrational frequency calculations were performed on the X ∼ 1 A 1 state of D 2CO at B3LYP, QCISD, CCSD and CASSCF levels, and the B ∼ 2 A 1 state of D 2CO + at CIS, TD-B3LYP, and CASSCF levels. Franck–Condon analyses and spectral simulations were carried out on the D 2 CO + ( B ∼ 2 A 1 ) - D 2 CO ( X ∼ 1 A 1 ) photoionization process. The spectral simulations of vibrational structures based on the computed Franck–Condon factors are in excellent agreement with the observed spectrum. In addition, the equilibrium geometric parameters of the B ∼ 2 A 1 state of D 2CO + were obtained in the spectral simulations.

Temperature effects on quasi-isolated conjugated polymers as revealed by temperature-dependent optical spectra of 16-mer oligothiophene diluted in a sold matrix

Temperature dependences (4-300 K) of photoluminescence (PL) and absorption spectra of 16-mer oligothiophene (16 T) extremely diluted in polypropylene (PP) have been investigated in order to clarify temperature effects on quasi-isolated conjugated polymers. The PL and absorption spectra are found to blueshift with increasing temperature. The reason for the blueshift is discussed by comparing models based on the refractive index of the solvent (PP) and on the thermal conformational change of 16 T. The blueshift is concluded to result from the thermal conformational change. Time-resolved PL spectra show a redshift of PL band following photoexcitation (spectral migration). The amount of the migration is shown to increase with increasing temperature. The increased migration is concluded to be due to the thermal conformational change. The temperature dependence of the effective conjugation length (ECL) of 16 T is calculated for the absorption and PL transitions. The calculation suggests that ECL is reduced at room temperature to two-thirds of the intrinsic chain length. The activation energy of the conformational change is estimated to be 22.4 meV from the temperature dependence of ECL. We demonstrate that the steady-state PL spectra are well reproduced by simple Franck-Condon analyses using a single Huang-Ryes factor over a wide temperature range. The analyses reveal features of temperature dependence in important spectral parameters such as the Stokes shift, linewidth, and Huang-Ryes factor.

A study of the ground and excited states of Al3 and Al3−. I. 488 nm anion photoelectron spectrum

The vibrationally resolved, 488 nm anion photoelectron spectrum of aluminum trimer displays transitions from two electronic states of Al(3)(-) to four states of Al(3). Franck-Condon analyses of the spectra in the independent harmonic oscillator, parallel mode approximation provide information concerning equilibrium bond length and bond angle differences among the observed states. The electron affinity of Al(3) is measured to be 1.916+/-0.004 eV. In the X (2)A(1)(') Al(3) ground state, fundamental symmetric stretching (nu(1)) and bending (nu(2)) vibrational frequencies are 357+/-10 and 240+/-10 cm(-1). In the X (1)A(1)(') Al(3)(-) ground state, these values are 365+/-15 and 257+/-15 cm(-1), and the equilibrium bond lengths are the same as those of Al(3) to within 0.02 A. The transition between the Al(3)(-) and Al(3) ground states displays only weak activity in the bending mode, consistent with essentially D(3h) structures for both states. An excited (3)B(2) Al(3)(-) state at 0.409+/-0.004 eV (T(0)) has vibrational frequencies of 330+/-20 (nu(1)) and 200+/-10 cm(-1) (nu(2)). This C(2v) state has a 65+/-1 degree apex bond angle and its two equal bond lengths are within 0.01 A of the ground state value. Liquid nitrogen cooling of the downstream portion of the approximately 60 cm long, 0.4-0.7 Torr flow tube anion source increases the observed relative population of this excited triplet state among the sampled anions, evidently slowing its relaxation to the singlet ground state. A (2)A(2)(") excited state of Al(3) lies 0.192+/-0.004 eV above the ground state and has frequencies of 315+/-15 (nu(1)) and 197+/-10 cm(-1) (nu(2)) and bonds 0.10+/-0.03 A longer than in the ground state. A (4)A(2) Al(3) excited state at 0.300+/-0.004 eV displays 315+/-15 (nu(1)) and 140+/-10 cm(-1) (nu(2)) vibrational frequencies. The Franck-Condon analysis of this state, which is accessed only from the (3)B(2) anion, indicates a C(2v) structure with a 69+/-2 degree apex bond angle and bonds 0.06+/-0.02 A longer than in the ground state. A (2)B(2) Al(3) excited state at 0.706+/-0.005 eV is also accessed from the (3)B(2) anion. The lack of vibrational features observable over overlapping transitions indicates similar structures for the (2)B(2) and (3)B(2) states. Primary stretching force constants (mdyn/A) are reported for the Al(3)(-) (0.70+/-0.06) and Al(3) (0.63+/-0.04) ground states and for three excited states. In the following paper, computational predictions for the ground and excited states of Al(3)(-) and Al(3) are reported and compared with these results.

Ab initio calculations and Franck–Condon analysis of photoelectron spectroscopy of CH 3OO − and CD 3OO −

Geometry optimization and harmonic vibrational frequency calculations were performed on the X ˜ 2 A ″ states of CH 3OO/CD 3OO and X ˜ 1 A ′ states of CH 3OO −/CD 3OO − at the B3LYP, QCISD and CCSD levels. The electron affinity energies of CH 3OO/CD 3OO were calculated at various theory levels. Franck–Condon analyses and spectral simulations were carried out on the X ˜ 2 A ″ - X ˜ 1 A ′ photodetachment processes. The spectral simulations of vibrational structures based on the computed Franck–Condon factors are in agreement with the observed spectra.