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The high-frequency O-H stretching vibrational overtone spectrum of the water trimer has been studied computationally. The water trimer has been approximated as three individually vibrating water monomers. An internal coordinate Hamiltonian is constructed for each triatomic monomer unit using an exact kinetic-energy operator within the Born-Oppenheimer approximation and the two O-H distances and the H-O-H bending angle as the internal coordinates. The potential-energy surface, PES, is calculated using the coupled cluster method with single, double, and perturbative triple excitations, CCSD(T), and augmented correlation-consistent polarized valence triple-zeta, aug-cc-pVTZ, basis set. The PES is improved applying the counterpoise correction. The finite differences method is used to obtain the dipole moment surface. Eigenvalues of the Hamiltonians are computed with the variational method. Finally, matrix isolation infrared data are used to optimize some PES parameters to improve the results.

Gas phase overtone spectra of dimethyl ether (ΔvCH=2–5) and acetone (ΔvCH=3) are measured using conventional near infrared (NIR) spectroscopy. Intracavity dye laser photoacoustic spectroscopy (IDL‐PAS) has been used to measure the ΔvCH=5–7 gas phase spectra of both dimethyl ether and acetone. Oscillator strengths are calculated using a harmonically coupled anharmonic oscillator local mode description to obtain the vibrational wave functions and ab initio molecular orbital (MO) calculations to obtain the dipole moment function. The calculations, which use no adjustable parameters, can account for the magnitude of the intensities and for the falloff in intensity with increasing v, for both molecules. It can also account reasonably well for the relative intensity of various peaks within a given vibrational manifold and for the relative intensity in the spectra of these two molecules and of propane.

A combination of vapor phase infrared spectroscopy and ab initio calculations has been used to show that sulfur is weaker than, but nearly equivalent to, oxygen as a hydrogen bond acceptor. Enthalpies of hydrogen bond formation were obtained for the hydrogen bonded complexes formed between methanol and either dimethyl sulfide or dimethyl ether by temperature dependence studies of the infrared spectra.

We have calculated electronic transitions for sulfuric acid in the ultraviolet region using a hierarchy of coupled cluster response functions and correlation consistent basis sets. Our calculations indicate that the lowest energy singlet transition occurs at 8.42 eV with an oscillator strength of 0.01. The lowest energy triplet state occurs at 8.24 eV. Thus, the cross section of sulfuric acid in the actinic region is likely to be very small and smaller than the upper limit put on this cross section by previous experimental investigations. We estimate the cross section of sulfuric acid in the atmospherically relevant Lyman-alpha region ( approximately 10.2 eV) to be approximately 6 x 10 (-17) cm (2) molecule (-1), a value approximately 30 times larger than the speculative value used in previous atmospheric simulations. We have calculated the J values for photodissociation of sulfuric acid with absorption of visible, UV, and Lyman-alpha radiation, at altitudes between 30 and 100 km. We find that the dominant photodissociation mechanism of sulfuric acid below 70 km is absorption in the visible region by OH stretching overtone transitions, whereas above 70 km, absorption of Lyman-alpha radiation by high energy Rydberg excited states is the favored mechanism. The low lying electronic transitions of sulfuric acid in the UV region do not contribute significantly to its dissociation at any altitude.

We have calculated frequencies and intensities of fundamental and overtone vibrational transitions in water and water dimer with use of different vibrational methods. We have compared results obtained with correlation-corrected vibrational self-consistent-field theory and vibrational second-order perturbation theory both using normal modes and finally with a harmonically coupled anharmonic oscillator local mode model including OH-stretching and HOH-bending local modes. The coupled cluster with singles, doubles, and perturbative triples ab initio method with augmented correlation-consistent triple-zeta Dunning and atomic natural orbital basis sets has been used to obtain the necessary potential energy and dipole moment surfaces. We identify the strengths and weaknesses of these different vibrational approaches and compare our results to the available experimental results.

We have calculated vertical excitation energies and oscillator strengths of the low lying electronic transitions in H2O, NH3, and H2O∙NH3 using a hierarchy of coupled cluster response functions [coupled cluster singles (CCS), second order approximate coupled cluster singles and doubles (CC2), coupled cluster singles and doubles (CCSD), and third order approximate coupled cluster singles, doubles, and triples (CC3)] and correlation consistent basis functions (n-aug-cc-pVXZ, where n=s,d,t and X=D,T,Q). Our calculations indicate that significant changes in the absorption spectra of the photodissociative states of H2O and NH3 monomers occur upon complexation. In particular, we find that the electronic transitions originating from NH3 are blueshifted, whereas the electronic transitions originating from H2O are redshifted.

We have calculated the band profiles of the OH-stretching fundamental and overtone transitions in the proton donor unit of the water dimer complex. We have used a local mode Hamiltonian that includes both OH-stretching and OO-stretching motion but separates these adiabatically. The variation of OH-stretching frequency and anharmonicity with OO displacement from equilibrium contributes to the effective OO-stretching potentials for each OH-stretching state. The resulting OO-stretching energy levels and wave functions are used to simulate the vibrational profile of each OH-stretching transition. The coupled cluster with singles, doubles, and perturbative triples ab initio method with an augmented triple-zeta correlation consistent basis set has been used to obtain the necessary parameters, potentials, and dipole moment functions. We find that the OO-stretching transitions associated with a given hydrogen bonded OH-stretching transition are spread significantly and this spread increases with overtone. The spread is minor for the free OH-stretching transition. The inclusion of the OO-stretching mode has a limited effect on the overall OH-stretching band intensity.

We describe theoretical methods for the calculation of vibrational and electronic transitions in sulfuric acid, from which absorption cross sections can be obtained in the infrared through to the vacuum ultraviolet region. In the absence of experimental cross sections these calculations provide invaluable input for the assessment of the atmospheric photolysis of sulfuric acid. The vibrational model is based on a local mode model that includes the OH-stretching and SOH-bending vibrations, while the electronic transitions are calculated with coupled cluster response theory. These approaches are sufficient to describe the dominant vibrational transitions in the near infrared and visible regions, the lowest lying electronic transitions in the ultraviolet region and the higher energy electronic transitions in the region of Lyman- α radiation. We highlight the influence quantum mechanical calculations have had in the recent discussion of the atmospheric photolysis of sulfuric acid, and show that theoretical calculations can provide absorption cross sections of an accuracy that is useful in atmospheric science.

The gas phase vibrational overtone spectrum of propane is measured using conventional near infrared (NIR) spectroscopy for the ΔvCH=2–5 regions and intracavity dye laser photoacoustic spectroscopy (IDL‐PAS) for the ΔvCH=5 and 6 regions. The peaks are assigned in terms of the local mode model. Experimental oscillator strengths are compared to values calculated for the CH‐stretching components of the spectrum. The calculations use a harmonically coupled, anharmonic oscillator local mode model to obtain the vibrational wave functions, and ab initio MO calculations at the SCF level with a 6‐31G* basis set to obtain the dipole moment function. The importance of intermanifold coupling is explored. The calculations can account for the fall‐off in intensity with increasing v, and can give a reasonably quantitative account of the relative intensities of the individual peaks within a given vibrational manifold. The questions of the relative intensities of primary and secondary CH bonds, and of the relative intensities of different methyl CH bonds are also explored.

The quantum mechanical Hamiltonian in curvilinear coordinates is obtained in a straightforward manner without using results from tensor analysis.

We have calculated the frequencies and intensities of the hydrogen-bonded OH-stretching transitions in the water dimer complex. The potential-energy curve and dipole-moment function are calculated ab initio at the coupled cluster with singles, doubles, and perturbative triples level of theory with correlation-consistent Dunning basis sets. The vibrational frequencies and wavefunctions are found from a numerical solution to a one-dimensional Schrödinger equation. The corresponding transition intensities are found from numerical integration of these vibrational wavefunctions with the ab initio calculated dipole moment function. We investigate the effect of counterpoise correcting both the potential-energy surface and dipole-moment function. We find that the effect of using a numeric potential is significant for higher overtones and that inclusion of a counterpoise correction for basis set superposition error is important.

Lipophilic monocations can pass through phospholipid bilayers and accumulate in negatively-charged compartments such as the mitochondrial matrix, driven by the membrane potential. This property is used to visualize mitochondria, to deliver therapeutic molecules to mitochondria and to measure the membrane potential. In theory, lipophilic dications have a number of advantages over monocations for these tasks, as the double charge should lead to a far greater and more selective uptake by mitochondria, increasing their therapeutic potential. However, the double charge might also limit the movement of lipophilic dications through phospholipid bilayers and little is known about their interaction with mitochondria. To see whether lipophilic dications could be taken up by mitochondria and cells, we made a series of bistriphenylphosphonium cations comprising two triphenylphosphonium moieties linked by a 2-, 4-, 5-, 6- or 10-carbon methylene bridge. The 5-, 6- and 10-carbon dications were taken up by energized mitochondria, whereas the 2- and 4-carbon dications were not. The accumulation of the dication was greater than that of the monocation methyltriphenylphosphonium. However, the uptake of dications was only described by the Nernst equation at low levels of accumulation, and beyond a threshold membrane potential of 90–100 mV there was negligible increase in dication uptake. Interestingly, the 5- and 6-carbon dications were not accumulated by cells, due to lack of permeation through the plasma membrane. These findings indicate that conjugating compounds to dications offers only a minor increase over monocations in delivery to mitochondria. Instead, this suggests that it may be possible to form dications within mitochondria that then remain within the cell.

We have calculated the equilibrium geometries of the hydrated complexes, H2O∙CO2, H2O∙CS2,H2O∙OCS, H2O∙SO2, and H2O∙SO3, in the electronic ground state. We have used the coupled cluster with singles, doubles, and perturbative triples ab initio method with a correlation consistent augmented triple-zeta basis set. We find that a counterpoise corrected optimization scheme is important for an accurate description of the geometries. These high level ab initio calculated geometries are of comparable quality to those obtained experimentally.

The spectroscopy of the vapor phase hydrogen bonded complex formed between methanol and trimethylamine has been studied in the near-infrared region. A combination band involving one quantum of OH stretch and one quantum of COH bend has been observed for the complex. The much less intense first OH-stretching overtone transition has been tentatively assigned. This assignment is supported by anharmonic oscillator local mode calculations.

We have recorded the vibrational absorption spectrum of 1,1,1,2-tetrafluoroethane (HFC-134a) in the fundamental and first five CH-stretching overtone regions with the use of Fourier transform infrared, dispersive long-path, intracavity laser photoacoustic, and cavity ringdown spectroscopies. We compare our measured total oscillator strengths in each region with intensities calculated using an anharmonic oscillator local mode model. We calculate intensities with 1D, 2D, and 3D Hamiltonians, including one or two CH stretches and two CH stretches with the HCH bending mode, respectively. The dipole moment function is calculated ab initio with self-consistent-field Hartree-Fock and density functional theories combined with double- and triple-zeta-quality basis sets. We find that the basis set choice affects the total intensity more than the choice of the Hamiltonian. We achieve agreement between the calculated and measured total intensities of approximately a factor of 2 or better for the fundamental and first five overtones.

We have measured the OH- and OD-stretching fundamental and overtone spectra of phenol and its deuterated isotopomers under jet-cooled conditions using nonresonant ionization detection spectroscopy and vapor-phase infrared (IR) and near-infrared (NIR) spectra at room temperature using conventional and photoacoustic spectroscopy. The OH- and OD-stretching bands in the jet-cooled spectra are about 1-10 cm(-1) wide and generally show a few Lorentzian shaped peaks. The bands in the room-temperature spectra have widths of 20-30 cm(-1) and display clear rotational profiles. The band profiles in the jet-cooled spectra arise mostly from nonstatistical intramolecular vibrational redistribution (IVR) with specific coupling to "doorway" states, which are likely to involve CH- and CD-stretching vibrations. The transition dipole moment that determines the rotational structure is found to rotate significantly from the fundamental to the third overtone and is not directed along the OH(D) bond. We use these calculated transition dipole moments to simulate the rotational structure. We determine the rotational temperature in the jet-cooled spectra to be about 0.5 K. Anharmonic oscillator local mode calculations of frequencies and intensities of the OH- and OD-stretching transitions are compared with our measured results. The calculated intensities are in good agreement with the absolute intensities obtained from conventional spectroscopy and with the relative intensities obtained from the room-temperature laser spectroscopy.

We report measurement and analysis of the photodissociation spectrum of hydroxymethyl hydroperoxide (HOCH(2)OOH) and its partially deuterated analogue, HOCD(2)OOH, in the OH-stretching region. Spectra are obtained by Fourier transform infrared spectroscopy in the 1nu(OH) and 2nu(OH) regions, and by laser induced fluorescence detection of the OH fragment produced from dissociation of HOCH(2)OOH initiated by excitation of the 4nu(OH) and 5nu(OH) overtone regions (action spectroscopy). A one-dimensional local-mode model of each OH chromophore is used with ab initio calculated OH-stretching potential energy and dipole moment curves at the coupled-cluster level of theory. Major features in the observed absorption and photodissociation spectra are explained by our local-mode model. In the 4nu(OH) region, explanation of the photodissocation spectrum requires a nonuniform quantum yield, which is estimated by assuming statistical energy distribution in the excited state. Based on the estimated dissociation threshold, overtone photodissociation is not expected to significantly influence the atmospheric lifetime of hydroxymethyl hydroperoxide.

We have simulated the HOONO vibrational overtone spectrum with use of a local mode Hamiltonian that includes the OH-stretching, OOH-bending, and NOOH-torsional modes and coupling between all three modes. The local mode parameters and the dipole moment function are calculated with coupled-cluster ab initio theory and an augmented Dunning-type triple-zeta basis set. We investigate the accuracy of the local mode parameters obtained from two different potential-energy fitting routines, as well as the sensitivity of these parameters to the basis set employed. We compare our simulated spectra to previously published action spectra in the first and second OH-stretching overtone regions. In addition we have recorded the spectrum in the OH-stretch and OOH-bend combination region around 7700 cm-1 and we also compare to this. Our simulated spectrum is in qualitative agreement with experiment in the first and second OH-stretching overtone and in the stretch-bend regions.

[1] We present the first microphysical calculations confirming that photolysis of sulfuric acid vapor by visible light is responsible for the formation of the springtime “CN layer” observed in the polar stratosphere. Our calculations show that the recently proposed photolysis mechanism is also sufficient to explain observations of vertically increasing SO2 mixing ratios in the upper stratosphere. Such photolysis, however, does not sufficiently explain the limited observations above 40 km of vertically decreasing H2SO4 and SO3 vapor, suggesting an additional loss mechanism there. We rule out previous speculation regarding reaction of H2SO4 with O(1D) or OH as inconsistent with observations of SO2. Rather, the loss is consistent with a permanent sink for sulfur, such as H2SO4 neutralization by metals on meteoritic dust. In light of such removal, H2SO4 photolysis to SO2 gains added importance in preserving gaseous sulfur in the upper stratosphere. We also present new cross sections derived from ab initio calculations for H2SO4 absorption at visible and Lyman-α wavelengths and evaluate their atmospheric implications. Our atmospheric model reveals that photolysis of H2SO4 by Lyman-α radiation is responsible for up to one third of the SO2 in the mesosphere and 10% of the particles in the polar stratospheric CN layer.

The lowest-energy electronic transitions in the hydroxyl radical and the hydrogen bound complex H(2)O.HO have been studied using ab initio methods. We have used the complete active-space self-consistent field and multireference configuration interaction (MRCI) methods to calculate vertical excitation energies and oscillator strengths. At the MRCI level the lowest-lying (2)Sigma(+)--(2)Pi electronic transition is redshifted by about 2500 cm(-1) upon formation of the H(2)O.HO complex. We propose that this transition could be used to identify the complex in the gas phase, which in turn could be used to examine the role of H(2)O.HO in atmospheric reactions.

[1] Estimates of absorption optical depths for the bound complexes H2O-H2O and the sum of H2O-N2, H2O-O2, and H2O-Ar at visible and near-infrared wavelengths are compared to the same quantities calculated from a frequently used water continuum parameterization (MT_CKD) and from a theoretical far wing water vapor lineshape theory. The temperature dependences of some of these optical depths are also compared. The comparisons suggest qualitatively that water complexes may contribute to the continuum at these wavelengths, and show that the temperature dependence of the continuum might provide insight into the role of the complexes in the atmosphere. Because of the dearth of laboratory measurements of the continuum at these wavelengths, and because the current estimates for the equilibrium constants of these water vapor complexes remain highly uncertain, more observations are needed before the importance of water complexes can be accurately quantified.

We have measured the infrared spectrum of H2O.HO in argon matrices at 11.5 +/- 0.5 K. We have also calculated the vibrational frequencies and intensities of the H2O.HO complex. As a result of these measurements and calculations, we have assigned a previously unassigned absorption band at 3442.1 cm-1 to the OH stretch in the radical complexed to the water molecule. This absorption originates from a complex that is situated in a different site within the argon matrix to those absorptions already assigned to this vibration at 3452.2 and 3428.0 cm-1. We observe a decrease in intensity of the OH radical stretching vibration of the H2O.HO complex upon isotopic substitution of D for H that agrees well with our calculations.

The water amidogen radical complex (H(2)O-NH(2)) is a reactive intermediate in the atmospheric oxidation of ammonia by a hydroxyl radical. In the present study, we identify for the first time the H(2)O-NH(2) complex using matrix isolation infrared spectroscopy. We corroborate our experimental findings with high level coupled cluster ab initio calculations.

The gas phase reaction between methane sulfonic acid (CH3SO3H; MSA) and the hydroxyl radical (HO), without and with a water molecule, was investigated with DFT-B3LYP and CCSD(T)-F12 methods. For the bare reaction we have found two reaction mechanisms, involving proton coupled electron transfer and hydrogen atom transfer processes that produce CH3SO3 and H2O. We also found a third reaction mechanism involving the double proton transfer process, where the products and reactants are identical. The computed rate constant for the oxidation process is 8.3 × 10(-15) cm(3) s(-1) molecule(-1). CH3SO3H forms two very stable complexes with water with computed binding energies of about 10 kcal mol(-1). The presence of a single water molecule makes the reaction between CH3SO3H and HO much more complex, introducing a new reaction that consists in the interchange of H2O between HO and CH3SO3H. Our kinetic calculations show that 99.5% of the reaction involves this interchange of the water molecule and, consequently, water vapor does not play any role in the oxidation reaction of methane sulfonic acid by the hydroxyl radical.

We have identified the dimethylamine-trimethylamine complex (DMA-TMA) at room temperature in the gas phase. The Fourier transform infrared (FTIR) spectrum of DMA-TMA in the NH-stretching fundamental region was obtained by spectral subtraction of spectra of each monomer. Explicitly correlated coupled cluster calculations were used to determine the minimum energy structure and interaction energy of DMA-TMA. Frequencies and intensities of NH-stretching transitions were also calculated at this level of theory with an anharmonic oscillator local mode model. The fundamental NH-stretching intensity in DMA-TMA is calculated to be approximately 700 times larger than that of the DMA monomer. The measured and calculated intensity is used to determine a room temperature equilibrium constant of DMA-TMA of 1.7 × 10(-3) atm(-1) at 298 K.

The gas phase hydrogen abstraction reaction between OH and CY(2)XH, where X = H, F, OH, or NH(2) and Y = H, CH(3) or F, in the absence and presence of a single water molecule is investigated using both density function theory, B3LYP, and explicitly correlated coupled cluster theory, CCSD(T)-F12. We find that a single water molecule could have a catalytic effect at low temperatures possible in laboratory experiments, but does not seem to catalyze these reactions at 298 K, and will not play a role under relevant atmospheric conditions.

We report experimental evidence for the formation of C5-hydroperoxyaldehydes (HPALDs) from 1,6-H-shift isomerizations in peroxy radicals formed from the hydroxyl radical (OH) oxidation of 2-methyl-1,3-butadiene (isoprene). At 295 K, the isomerization rate of isoprene peroxy radicals (ISO∙_2) relative to the rate of reaction of (ISO∙_2) + HO_2 is (k^(295)_(isom))/(k^(295)_((ISO∙_2) + HO_2) = (1.2±0.6) × 10^8 mol cm^(-2), or k^(295)_(isom)≃0.002 s^(-1). The temperature dependence of this rate was determined through experiments conducted at 295, 310 and 318 K and is well described by (k_(isom))T))/(k_((ISO∙_2)+HO_2) (T) = 2.0 × 10^(21) exp(-9000/T)mol cm^(-3). The overall uncertainty in the isomerization rate (relative to k_((ISO∙_2)+HO_2) is estimated to be 50%. Peroxy radicals from the oxidation of the fully deuterated isoprene analog isomerize at a rate of ~15 times slower than non-deuterated isoprene. The fraction of isoprene peroxy radicals reacting by 1,6-H-shift isomerization is estimated to be 8–11% globally, with values up to 20% in tropical regions.

Claeys questions whether gaseous epoxydiol is formed from the oxidation of isoprene and whether it is relevant to the formation of isoprene-derived secondary organic aerosol (iSOA). We argue that the alternative mechanism she proposes for iSOA applies primarily to chamber studies with high isoprene and is not as important in the atmosphere, where isoprene concentrations are much lower.

We investigate the OH-stretching overtone dynamics of fluorosulfonic acid (FSO(3)H) and chlorosulfonic acid (ClSO(3)H) using classical trajectory simulations. The initial nuclear coordinates and momenta for the trajectories are sampled from anharmonic correlation-corrected vibrational self consistent field (CC-VSCF) wavefunctions. We consider both OH-stretching overtone states and combination states containing a mix of OH-stretching overtones and SOH-bending or OSOH-torsional modes. Our molecular dynamics simulations confirm that photodissociation of these sulfonic acids to form the corresponding hydrogen halides and sulfur trioxide (HF + SO(3) and HCl + SO(3)), is possible via highly vibrationally excited states on a picosecond timescale. Hydrogen-hopping events are also observed in the trajectories whereby the hydrogen atom of the excited OH group is found to migrate to one of the adjacent S=O groups. The transition states, activation energies and dissociation dynamics of FSO(3)H and ClSO(3)H are found to be similar to those of H(2)SO(4). We suggest that these halogenated sulfonic acids should be suitable proxy molecules for an experimental investigation of the OH-stretching overtone induced photodissociation of H(2)SO(4) thought to be important in Earths' atmosphere.

Vertical and adiabatic excitation energies of the lowest (2)A(') excited state in the water-hydroxyl complex have been determined using coupled cluster, multireference configuration interaction, multireference perturbation theory, and density-functional methods. A significant redshift of about 0.4 eV in the vertical excitation energy of the complex compared to that of the hydroxyl radical monomer is found with the coupled cluster calculations validating previous results. Electronic excitation leads to a structure with near-equal sharing of the hydroxyl hydrogen by both oxygen atoms and a concomitantly large redshift of the adiabatic excitation energy of approximately 1 eV relative to the vertical excitation energy. The combination of redshifts ensures that the electronic transition in the complex lies well outside the equivalent excitation in the hydroxyl radical monomer. The complex is approximately five times more strongly bound in the excited state than in the ground state.

The room-temperature vibrational overtone spectra of the formic acid isotopomers HCOOH and DCOOH have been recorded in the third and fourth OH-stretching overtone regions with intracavity laser photoacoustic spectroscopy. Resonance coupling between the OH- and CH-stretching vibrations in HCOOH is clearly identified in the fourth overtone region. This is an example of strong coupling across bonds. In the third overtone region, no resonance is observed. Vibrational energies and intensities of the OH- and CH-stretching overtones and combination bands have been calculated with an anharmonic oscillator local mode model. The pure OH-stretching bright state carries almost all the intensity prior to resonance coupling.

The room temperature vibrational overtone spectrum of aniline vapour has been recorded by intracavity laser photoacoustic spectroscopy in the 9700 cm−1 to 16 600 cm−1 region. The NH-stretching overtone bands exhibit spectral structure due to the tunneling splitting of the amino group inversion states. We find that this tunneling splitting steadily decreases with increasing NH-stretching vibrational excitation, and at the fourth NH-stretching overtone the splitting is negligible. Wave numbers and intensities of the NH- and CH-stretching vibrational overtones were calculated with a harmonically coupled anharmonic oscillator local mode model to facilitate spectral assignment. The conventional liquid phase overtone spectra of aniline were recorded and the measured absolute intensities are in good agreement with the calculated intensities.

We have calculated the fundamental and overtone OH-stretching and HOH-bending vibrational spectrum of the water dimer up to 20 000 cm−1. The calculated frequencies and intensities of the transitions up to 8000 cm−1 agree well with previously recorded matrix isolation spectra. We compare our calculated spectrum of the water dimer to the observed water monomer spectrum, and suggest regions in which spectral features due to the water dimer are most likely to be observed in the laboratory and our atmosphere.

An analysis of the structure, vibrational and electronic spectra, and the molecular orbitals of 2,6-diazaanthracene-9,10-dione (DAAD) (1) and its radical anion is presented. Strong π-stacking is seen in the crystal structure of (1) and observed bond lengths and angles are in good agreement with those calculated with the B3LYP/6-31G(d) method. The vibrational spectra of (1) show strong bands at 1686 cm–1 (IR) and 1676 cm–1 (Raman) corresponding to the antisymmetric and symmetric C=O stretch, respectively, in good agreement with calculated data. Electrochemical or chemical reduction to (1)•- results in a new spectrum with a strong absorption due to the antisymmetric stretch at 1481 cm–1 (predicted 1470 cm–1). The lowest energy electronic transition for (1) occurs at 317 nm; new transitions at lower energy (403, 573, and 910 nm) are seen in the spectrum of (1)•-. The dark purple radical anion (1)•- was isolated as the Cp2Co+ salt but its ESR spectrum did not display hyperfine coupling.