Dibenzo-p-dioxin. An ab initio CASSCF/CASPT2 study of the pi-pi* and n-pi* valence excited states

The pi-pi* and n-pi* valence excited states of dibenzo-p-dioxin (DD) were studied via the complete active space SCF and multiconfigurational second-order perturbation theory employing the cc-pVDZ basis set and the full pi-electron active spaces of 16 electrons in 14 active orbitals. The geometry and harmonic vibrational wavenumbers of the ground state correlate well with the experimental and other theoretical data. In particular, significant improvements over previously reported theoretical results are observed for the excitation energies. All of the pi-pi* excited states exhibit planar D(2h)minima. Thus no evidence was found for a C(2v) butterfly-like relaxation, although the wavenumbers of the b(3u) butterfly flapping mode proved exceedingly low in both the ground S(0)((1)A(g)) and the lowest dipole allowed excited S(1)((1)B(2u)) state. The calculations of oscillator strengths established the 2(1)B(2u) <-- 1(1)A(g) and 2(1)B(1u) <-- 1(1)A(g) transitions as by far the most intense, whereas the only allowed of the n-pi* transitions ((1)B(3u)) should possess only a modest intensity. Studies into dependence of the oscillator strengths on the extent of the butterfly-like folding showed that the electronic spectrum is more consistent with a folded equilibrium geometry assumed by DD in solution.     

Electronic transitions in [Re6S8X6](4-) (X = Cl, Br, I): results from time-dependent density functional theory and solid-state calculations

Relativistic time-dependent density functional theory (TDDFT) calculations were performed on the excited states of the [Re6S8X6](4-) (X = Cl, Br, I) series. For all members of the series, the lowest excited states in the spectra do not correspond to a ligand-to-metal (or ligand-to-cluster) excitation but rather a cluster-cluster transition from the HOMO e(g) to antibonding t(1u) orbitals with only a modest admixture of Re-X sigma* character. These results lead to a re-evaluation of the role of the axial ligand in these compounds. The calculated excitation energies reproduce the experimental absorption and emission spectra. This work also confirms previous TDDFT calculations on the emission energies. Results for discrete cluster ions are compared with those obtained from calculations in the solid state in Cs4[Re6S8X6].CsX (X = Cl, Br) and Cs4[Re6S8I6].2CsI. Significant differences are seen in the relatively higher energies of the antibonding t(1u) orbital in the solid-state case, and an inversion in the orbital character of the two allowed absorptions is calculated. The e(g) (HOMO)-to-a(2g) (LUMO) orbital energy differences corresponding to the emission transition are quite comparable for the solid state and discrete cluster calculations, and both overestimate the observed emission energy by the same margin.     

Quantum chemical modeling of photoadsorption properties of the nitrogen-vacancy point defect in diamond

Quantum chemical calculations of geometric and electronic structure and vertical transition energies for several low-lying excited states of the neutral and negatively charged nitrogen-vacancy point defect in diamond (NV(0) and NV(-)) have been performed employing various theoretical methods and basis sets and using finite model NC(n)H(m) clusters. Unpaired electrons in the ground doublet state of NV(0) and triplet state of NV(-) are found to be localized mainly on three carbon atoms around the vacancy and the electronic density on the nitrogen and rest of C atoms is only weakly disturbed. The lowest excited states involve different electronic distributions on molecular orbitals localized close to the vacancy and their wave functions exhibit a strong multireference character with significant contributions from diffuse functions. CASSCF calculations underestimate excitation energies for the anionic defect and overestimate those for the neutral system. The inclusion of dynamic electronic correlation at the CASPT2 level leads to a reasonable agreement (within 0.25 eV) of the calculated transition energy to the lowest excited state with experiment for both systems. Several excited states for NV(-) are found in the energy range of 2-3 eV, but only for the 1(3)E and 5(3)E states the excitation probabilities from the ground state are significant, with the first absorption band calculated at approximately 1.9 eV and the second lying 0.8-1 eV higher in energy than the first one. For NV(0), we predict the following order of electronic states: 1(2)E (0.0), 1(2)A(2) (approximately 2.4 eV), 2(2)E (2.7-2.8 eV), 1(2)A(1), 3(2)E (approximately 3.2 eV and higher).     

Relativistic calculations of ground and excited states of LiYb molecule for ultracold photoassociation spectroscopy studies

We report a series of quantum-chemical calculations for the ground and some of the low-lying excited states of an isolated LiYb molecule by the spin-orbit multistate complete active space second-order perturbation theory (SO-MS-CASPT2). Potential energy curves, spectroscopic constants, and transition dipole moments (TDMs) at both spin-free and spin-orbit levels are obtained. Large spin-orbit effects especially in the TDMs of the molecular states dissociating to Yb((3)P(0,1,2)) excited states are found. To ensure the reliability of our calculations, we test five types of incremental basis sets and study their effect on the equilibrium distance and dissociation energy of the ground state. We also compare CASPT2 and CCSD(T) results for the ground state spectroscopic constants at the spin-free relativistic level. The discrepancies between the CASPT2 and CCSD(T) results are only 0.01 ? in equilibrium bond distance (R(e)) and 200 cm(-1) in dissociation energy (D(e)). Our CASPT2 calculation in the supermolecular state (R=100 a.u.) with the largest basis set reproduces experimental atomic excitation energies within 3% error. Transition dipole moments of the super molecular state (R=100 a.u.) dissociating to Li((2)P) excited states are quite close to experimental atomic TDMs as compared to the Yb((3)P) and Yb((1)P) excited states. The information obtained from this work would be useful for ultracold photoassociation experiments on LiYb.     

Computational investigation of the vibrational and electronic states of S2N2

The structures and vibrational frequencies of the ground and excited states of S(2)N(2) have been calculated using density functional (DF) methods. Time-dependent DF theory (TDDFT) has been used to calculate the excitation energies of the lowest 20 singlet-singlet transitions using a variety of methods. All computational methods predict a small highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap. There is some disagreement in the ordering of the b(2g) and b(3g) pi orbitals. This is reflected in the ordering of the B(2u) and B(3u) states from the TDDFT calculations. The excitation energies and oscillator strengths strongly suggest it is the transitions to these states that are responsible for the experimental electronic spectrum. The calculated geometries and vibrational frequencies for these two states show that both have C(2v) equilibrium structures. Modelling of the vibrational progressions and band shapes suggest that the ordering of the states is B(2u)相似文献   

Potentials of the D¹0u⁺ (6¹S₀) and F³1u(6³P₂) electronic Rydberg states of Cd₂ from ab initio calculations and laser-induced fluorescence excitation spectra

The method of supersonic free-jet expansion beam combined with techniques of laser spectroscopy was used in an investigation of vibronic and isotopic structures in the D10(u)? (61S?) and F31(u)(63P?) electronic energy Rydberg states of Cd?. Laser-induced fluorescence excitation spectra recorded using the D10(u)? ← X10(g)?(51S?) and F31(u) ← X10(g)? transitions in the region of 206-218 nm provided spectroscopic characteristics of the excited states and allowed constructing of their intratomic potentials. Isotopic structures recorded in the (υ',υ') bands of the D10(u)? ← X10(g)? transition were used in determination of the D10(u)? state vibrational characteristics (ω'(e)x'(e), ω'(e)x'(e)) and υ' assignment. The ν(0,0) recorded directly in the F31(u) ← X10(g)? transition enabled determination of the bottom of the F31(u) state potential well. Valence ab initio calculations of Cd? interatomic potentials were performed with relativistic and spin-orbit effects taken into account. The experimental results were compared with results of the ab initio calculations. A free-jet expansion of Cd? as a source of entangled atoms for a test of Bell's inequality was analyzed.     

Symmetry switching of the fluorescent excited state in alpha,omega-diphenylpolyynes

By using MO calculations based on DFT, absorption, and fluorescence spectroscopy, we have comprehensively studied the low-lying excited singlet states of alpha,omega-diphenylpolyynes (DPY) having 1-6 triple bonds. The a(g) vibrational modes of the C(triple bond)C stretching and of the phenyl ring motion were observed in the fluorescence spectra of diphenylacetylene and 1,4-diphenylbutadiyne. On the other hand, in the fluorescence spectra of the long DPY with the triple-bond number (N) more than two, the phenyl ring motion with a(g) symmetry disappeared and the b(1g) modes of the phenyl ring twisting (approximately 400 cm(-1)) and of the C-H bending (approximately 900 cm(-1)) were detected. The observed fluorescent states of DPY with N < or = 2 and N > or = 3 are assigned to the 1(1)B(1u) (pi(x)pi(x*)) and 1(1)A(u) (pi(x)pi(y*) and/or pi(y)pi(x*)) states, respectively, based on the vibronic structures, the relatively short lifetimes, and the solvatochromic shifts of the fluorescence spectra. Not only the allowed transition of 1(1)B(1u) <-- S(0) but also the forbidden transition of 1(1)A(u) <-- S(0) was detected in the fluorescence excitation spectra of the long DPY with N > or = 3. The low-lying excited state with A(u) symmetry is characteristic in polyyne, which does not exist in polyene. The oscillator strength (f) of the first absorption band in DPY decreases with an increase in N, which is the opposite behavior of the all-trans-alpha,omega-diphenylpolyenes. The N-dependence of the f value is understood by the configuration interaction between the 1(1)B(1u) and 2(1)B(1u) (pi(y)pi(y*)) states, which is consistent with the reduction of the nonlinear optical response of polyyne.     

Density functional theory investigation of Eu(III) complexes with beta-diketonates and phosphine oxides: model complexes of fluorescence compounds for ultraviolet LED devices

The density functional theory was employed to investigate Eu(III) complexes with three beta-diketonates and two phosphine oxides (complex M1: Eu(bdk)3(TPPO)2, complex M2: Eu(bdk)3(TMPO)2, and complex M3: Eu(bdk)3(TPPO)(TMPO)) deemed to be the model complexes of the fluorescence compounds for the ultraviolet LED devices we have recently developed. For each complex, two minimum energy points corresponding to two different optimized geometries (structures A and B) have been found, and the difference of the energy between two minimum energy points is found to be quite small (less than 1 kcal/mol). Vertical excitation energies and oscillator strengths for each complex at two optimized geometries have been obtained by the time-dependent density functional theory, and the character of the excited states has been investigated. For complex M3, the absorption edge is red-shifted, and the oscillator strengths are relatively large. The efficiency of intersystem crossing and energy transfer from the triplet excited state to the Eu(III) ion is considered by calculating DeltaE(ISC) (the energy difference between the first singlet excited state and the first triplet excited state) and DeltaE(ET) (the difference between the excitation energy of the complex for the first triplet excited state and the emission energy of the Eu(III) ion for 5D to 7F).     

Electronic structures of low-lying Bu excited states in trans-oligoenes: Pariser-Parr-Pople and ab initio calculations

Two lowest-lying excited singlets with B(u) symmetry of all-trans-oligoenes, the well-known ionic 1(1)B(u)(+) state as well as the "hidden" ionic-covalent-mixed 1(1)B(u)(-) state, are calculated within both the Pariser-Parr-Pople (PPP) model at full configuration interaction (FCI) level and ab initio methods. The vertical excitation energies as well as wavefunctions from PPP-FCI calculations are found to be in good agreement with those from high-level multi-reference methods, such as multi-reference complete active space self-consistent field (CASSCF) with second order perturbative corrections (CASPT2), multi-reference M?ller-Plesset perturbation theory (MRMP), and complete active space valence bond theory (CASVB). The oscillator strengths from PPP calculation are in good agreement with spectroscopy experiments. The relatively small oscillator strength of 1(1)B(u)(-) is due to the approximate electron-hole symmetry of this state. In addition, the bond lengths in both states are found to show remarkable relativity with the bond orders calculated with ground state geometries, which suggests a possible strategy for initial guess in geometry optimization of excited states.     

Rydberg-valence mixing in the carbon 1s near-edge X-ray absorption fine structure spectra of gaseous alkanes

We have acquired high-resolution carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of methane, ethane, propane, isobutane, and neopentane. These experimental measurements are complemented by high-quality ab initio calculations, performed with the improved virtual orbital approximation. The degree and character of Rydberg-valence mixing in the preedge of the NEXAFS spectra of these species is explored. Significant Rydberg-valence mixing only occurs when there are excited states of valence sigma(C-H) character that have the appropriate symmetry to interact with excited states of Rydberg character. Our results show that this mixing is only present when there are C-H bonds to the core excited carbon atom.     

Theoretical investigations of the perylene electronic structure: Monomer,dimers, and excimers

The structural and electronic properties of perylene molecule, dimers, and excimers have been computationally studied. The present work represents the first systematic study of perylene molecule and dimer forms by means of long‐range corrected time‐dependent density functional theory (TDDFT) approaches. Initially, the study explores the photophysical properties of the molecular species. Vertical transitions to many excited singlet states have been computed and rationalized with different exchange‐correlation functionals. Differences between excitation energies are discussed and compared to the absorption spectrum of perylene in gas phase and diluted solution. De‐excitation energy from the relaxed geometry of the lowest excited singlet is in good agreement with the experimental fluorescence emission. Optimization of several coplanar forms of the perylene pair prove that, contrary to generalized gradient approximation (GGA) and hybrid exchange‐correlation functionals, corrected TDDFT is able to bind the perylene dimer in the ground state. Excitation energies from different dimer conformers point to dimer formation prior to photoexcitation. The fully relaxed excimer geometry belongs to the perfectly eclipsed conformation with D_2h symmetry. The excimer equilibrium intermolecular distance is shorter than the separation found for the ground state, which is an indication of stronger interchromophore interaction in the excimer state. Excimer de‐excitation energy is in rather good agreement with the excimer band of perylene in concentrated solution. The study also scans the energy profiles of the ground and lowest excited states along several geometrical distortions. The nature of the interactions responsible for the excimer stabilization is explored in terms of excitonic and charge resonance contributions. © 2015 Wiley Periodicals, Inc.     

Theoretical investigation of excited states of C(3)

In this work, we present ab initio calculations for the potential energy surfaces of C(3) in different electronic configurations, including the singlet ground state [X (1)Sigma(g) (+),((1)A(1))], the triplet ground state [a (3)Pi(u),((3)B(1), (3)A(1))], and some higher excited states. The geometries studied include triangular shapes with two identical bond lengths, but different bond angles between them. For the singlet and triplet ground states in the linear geometry, the total energies resulting from the mixed density functional--Hartree-Fock and quadratic configuration interaction methods reproduce the experimental values, i.e., the triplet occurs 2.1 eV above the singlet. In the geometry of an equilateral triangle, we find a low-lying triplet state with an energy of only 0.8 eV above the energy of the singlet in the linear configuration, so that the triangular geometry yields the lowest excited state of C(3). For the higher excited states up to about 8 eV above the ground state, we apply time-dependent density functional theory. Even though the systematic error produced by this approach is of the order of 0.4 eV, the results give different prospective to insight into the potential energy landscape for higher excitation energies.     

Photoelectron spectroscopy of higher bromine and iodine oxide anions: electron affinities and electronic structures of BrO(2,3) and IO(2-4) radicals

This report details a photoelectron spectroscopy (PES) and theoretical investigation of electron affinities (EAs) and electronic structures of several atmospherically relevant higher bromine and iodine oxide molecules in the gas phase. PES spectra of BrO(2)(-) and IO(2)(-) were recorded at 12 K and four photon energies--355 nm/3.496 eV, 266 nm/4.661 eV, 193 nm/6.424 eV, and 157 nm/7.867 eV--while BrO(3)(-), IO(3)(-), and IO(4)(-) were only studied at 193 and 157 nm due to their expected high electron binding energies. Spectral features corresponding to transitions from the anionic ground state to the ground and excited states of the neutral are unraveled and resolved for each species. The EAs of these bromine and iodine oxides are experimentally determined for the first time (except for IO(2)) to be 2.515 ± 0.010 (BrO(2)), 2.575 ± 0.010 (IO(2)), 4.60 ± 0.05 (BrO(3)), 4.70 ± 0.05 (IO(3)), and 6.05 ± 0.05 eV (IO(4)). Three low-lying excited states along with their respective excitation energies are obtained for BrO(2) [1.69 (A (2)B(2)), 1.79 (B (2)A(1)), 1.99 eV (C (2)A(2))], BrO(3) [0.7 (A (2)A(2)), 1.6 (B (2)E), 3.1 eV (C (2)E)], and IO(3) [0.60 (A (2)A(2)), 1.20 (B (2)E), ～3.0 eV (C (2)E)], whereas six excited states of IO(2) are determined along with their respective excitation energies of 1.63 (A (2)B(2)), 1.73 (B (2)A(1)), 1.83 (C (2)A(2)), 4.23 (D (2)A(1)), 4.63 (E (2)B(2)), and 5.23 eV (F (2)B(1)). Periodate (IO(4)(-)) possesses a very high electron binding energy. Only one excited state feature with 0.95 eV excitation energy is shown in the 157 nm spectrum. Accompanying theoretical calculations reveal structural changes from the anions to the neutrals, and the calculated EAs are in good agreement with experimentally determined values. Franck-Condon factors simulations nicely reproduce the observed vibrational progressions for BrO(2) and IO(2). The low-lying excited state information is compared with theoretical calculations and discussed with their atmospheric implications.     

A clue to the diffuse structure in ultraviolet spectra of the GeCl2 A-X transition

Geometries, harmonic vibrational frequencies, and relative electronic energies of the two low-lying electronic states of the GeCl(2) dimer have been calculated at the CIS(D) method with a cc-pVTZ basis set. Minima corresponding to three isomers on the ground-state potential energy surface have been characterized. The most stable dimer has a dissociation energy of 0.74 eV and has a trans-(GeCl(2))(2) structure. There is also a related, less stable, cis minimum. A third, C(i) symmetry, isomer has a binding energy of 0.31 eV. It is found that this C(i) isomer has substantial dipole transition strength to the first excited singlet state of the dimer with a vertical excitation energy of 3.33 eV. The transition energy (T(0)) between this C(i) isomer and the van der Waals complex on the singlet excited state is predicted to be 4.007 eV, or a 1104 cm(-1) blueshift with respect to that of the GeCl(2) A-X transition. This finding may explain the diffuse structure which has been observed in the ultraviolet laser-induced fluorescence spectra of GeCl(2).     

Photodissociation dynamics of N2O at 130 nm: the N2(A 3Sigmau +,B 3Pig)+O(3PJ = 2,1,0) channels

Oxygen Rydberg time-of-flight spectroscopy was used to study the vacuum ultraviolet photodissociation dynamics of N(2)O near 130 nm. The O((3)P(J)) products were tagged by excitation to high-n Rydberg levels and subsequently field ionized at a detector. In agreement with previous work, we find that O((3)P(J)) formation following excitation to the repulsive N(2)O D((1)Sigma(+)) state produces the first two electronically excited states of the N(2) counterfragment, N(2)(A (3)Sigma(u) (+)) and N(2)(B (3)Pi(g)). The O((3)P(J)) translational energy distribution reveals that the overall branching ratio between N(2)(A (3)Sigma(u) (+)) and N(2)(B (3)Pi(g)) formation is approximately 1.0:1.0 for J = 1 and 2, with slightly less N(2)(B (3)Pi(g)) produced in coincidence with O((3)P(0)). The angular distributions were found to be independent of J and highly anisotropic, with beta = 1.5+/-0.2.     

Femtosecond time- and wavelength-resolved fluorescence and absorption spectroscopic study of the excited states of adenosine and an adenine oligomer

By employing broadband femtosecond Kerr-gated time-resolved fluorescence (KTRF) and transient absorption (TA) techniques, we report the first (to our knowledge) femtosecond combined time- and wavelength-resolved study on an ultraviolet-excited nucleoside and a single-stranded oligonucleotide (namely adenosine (Ado) and single-stranded adenine oligomer (dA)(20)) in aqueous solution. With the advantages of the ultrafast time resolution, the broad spectral and temporal probe window, and a high sensitivity, our KTRF and TA results enable the real time monitoring and spectral characterization of the excited-state relaxation processes of the Ado nucleoside and (dA)(20) oligonucleotide investigated. The temporal evolution of the 267 nm excited Ado KTRF spectra indicates there are two emitting components with lifetimes of approximately 0.13 ps and approximately 0.45 ps associated with the L(a) and L(b) pipi* excited states, respectively. These Ado results reveal no obvious evidence for the involvement of the npi* state along the irradiative internal conversion pathway. A distinct mechanism involving only the two pipi* states has been proposed for the ultrafast Ado deactivation dynamics in aqueous solution. The time dependence of the 267 nm excited (dA)(20) KTRF and TA spectra reveals temporal evolution from an ultrafast "A-like" state (with a approximately 0.39 ps decay time) to a relatively long-lived E(1) "excimer" (approximately 4.3 ps decay time) and an E(2) "excimer-like" (approximately 182 ps decay time) state. The "A-like" state has a spectral character closely resembling the excited state of Ado. Comparison of the spectral evolution between the results for Ado and (dA)(20) provides unequivocal evidence for the local excitation character of the initially photoexcited (dA)(20). The rapid transformation of the locally excited (dA)(20) component into the delocalized E(1) "excimer" state which then further evolves into the E(2) "excimer-like" state indicates that base stacking has a high ability to modify the excited-state deactivation pathway. This modification appears to occur by suppressing the internal conversion pathway of an individually excited base component where the stacking interaction mediates efficient interbase energy transfer and promotes formation of the collective excited states. This feature of the local excitation that is subsequently followed by rapid energy delocalization into nearby bases may occur in many base multimer systems. Our results provide an important new contribution to better understanding DNA photophysics.     

Theoretical study on the singlet excited state of pterin and its deactivation pathway

The excited-state properties and related photophysical processes of the acidic and basic forms of pterin have been investigated by the density functional theory and ab initio methodologies. The solvent effects on the low-lying states have been estimated by the polarized continuum model and combined QM/MM calculations. Calculations reveal that the observed two strong absorptions arise from the strong pi --> pi* transitions to 1(pipi*L(a)) and 1(pipi*L(b)) in the acidic and basic forms of pterin. The first 1(pipi*L(a)) excited state is exclusively responsible for the experimental emission band. The vertical 1(n(N)pi*) state with a small oscillator strength, slightly higher in energy than the 1(pipi*L(a)) state, is less accessible by the direct electronic transition. The 1(n(N)pi*) state may be involved in the photophysical process of the excited pterin via the 1(pipi*L(a)/n(N)pi*) conical intersection. The radiationless decay of the excited PT to the ground state experiences a barrier of 13.8 kcal/mol for the acidic form to reach the (S(1)/S(0)) conical intersection. Such internal conversion can be enhanced with the increase in excitation energy, which will reduce the fluorescence intensity as observed experimentally.     

Excited state properties of 7-hydroxy-4-methylcoumarin in the gas phase and in solution. A theoretical study

TDDFT/B3LYP and RI-CC2 calculations with different basis sets have been performed for vertical and adiabatic excitations and emission properties of the lowest singlet states for the neutral (enol and keto), protonated and deprotonated forms of 7-hydroxy-4-methylcoumarin (7H4MC) in the gas phase and in solution. The effect of 7H4MC-solvent (water) interactions on the lowest excited and fluorescence states were computed using the Polarizable Continuum Method (PCM), 7H4MC-water clusters and a combination of both approaches. The calculations revealed that in aqueous solution the pi pi* energy is the lowest one for excitation and fluorescence transitions of all forms of 7H4MC studied. The calculated excitation and fluorescence energies in aqueous solution are in good agreement with experiment. It was found that, depending on the polarity of the medium, the solvent shifts vary, leading to a change in the character of the lowest excitation and fluorescence transition. The dipole-moment and electron-density changes of the excited states relative to the ground state correlate with the solvation effect on the singlet excited states and on transition energies, respectively. The calculations show that, in contrast to the ground state, the keto form has a lower energy in the pi pi* state as compared to enol, demonstrating from this point of view the energetic possibility of proton transfer from the enol to the keto form in the excited state.     

Theoretical study of the benzene excimer using time-dependent density functional theory

A theoretical characterization of the potential energy surfaces of the singlet benzene excimer states derived from the B2u monomer excited state has been performed using time-dependent density functional theory. The excited-state potential energy surfaces were initially characterized by computations along the parallel and perpendicular intermolecular translational coordinates. These calculations predict that the lowest excited state for parallel translation is bound with a minimum at 3.15 angstroms and with a binding energy of 0.46 eV, while the perpendicular translational coordinate was essentially found to be a repulsive state. At the calculated minimum distance, the effect of in-plane rotation, out-of-plane rotation, and slipped-parallel translation were examined. The rotational calculations predict that deviations from the D6h geometry lead to a destabilization of the excimer state; however, small angular variations in the range of 0 degrees -10 degrees are predicted to be energetically feasible. The slipped-parallel translational calculations also predict a destabilizing effect on the excimer state and were found to possess barriers to this type of dissociation in the range of 0.50-0.61 eV. When compared to experimentally determined values for the benzene excimer energetics, the calculated values were found to be in semiquantitative agreement. Overall, this study suggests that the time-dependent density functional theory method can be used to characterize the potential energy surfaces and the energetics of aromatic excimers with reasonable accuracy.