Slow electron velocity-map imaging photoelectron spectra of the methoxide anion

High resolution anion photodetachment spectra are presented for the methoxide anion and its fully deuterated counterpart. The spectra were obtained with slow electron velocity-map imaging. Improved electron affinities are determined for CH3O as 1.5690+/-0.0019 eV and for CD3O as 1.5546+/-0.0019 eV. The spectra resolve many features associated with spin-orbit and vibronic coupling that were not seen in previous photodetachment studies. Photoelectron angular distributions taken as a function of detachment wavelength for the ground vibronic state transitions are recorded and are consistent with the removal of a nonbonding, p-type electron localized on the oxygen atom. Several hot bands and sequence bands are observed for the first time, providing insight into the vibrational structure of the methoxide anion. The results are compared to recent calculations of the anion photoelectron spectra that incorporate bilinear coupling terms among the methoxy vibrational modes and are found to be in reasonable agreement.     

ZEKE-PFI spectroscopy of benzocaine

The adiabatic ionization threshold (AIT) of trans- and gauche-benzocaine has been measured by zero electron kinetic energy-pulsed field ionization (ZEKE-PFI) spectroscopy to be 7.8412+/-0.0008 eV (lasers at 34,134.4 and 29,109.3 cm(-1)) and 7.8421+/-0.0004 eV (34,144.8+29105.7 cm(-1)), respectively. AITs computed at the B3LYP/AUG-cc-p-VDZ level for the two conformers are some approximately 2,500 cm(-1) lower than the experimental; in contrast their energy difference is very close. The trans-benzocaine cation ZEKE spectra has been recorded taking a number of S(1) intermediate vibronic states. The spectra provide an energy threshold for the appearance of intramolecular vibrational redistribution (IVR) around approximately 540 cm(-1) in the S(1) state.     

A vacuum ultraviolet pulsed field ionization-photoelectron study of cyanogen cation in the energy range of 13.2-15.9 eV

The vacuum ultraviolet pulsed field ionization-photoelectron and photoionization efficiency spectra of NCCN have been measured in the energy region of 13.25-17.75 eV. The analyses of these spectra have provided accurate ionization energy (IE) values of 13.371+/-0.001, 14.529+/-0.001, 14.770+/-0.001, and 15.516+/-0.001 eV for the formation of NCCN(+) in the X(2)Pi(g), A(2)Sigma(g) (+), B(2)Sigma(u) (+), and C(2)Pi(u) states, respectively. The ionization energy [NCCN(+)(B(2)Sigma(u) (+))] value determined here indicates that the origin of the NCCN(+)(B(2)Sigma(u) (+)) state lies lower in energy by 25 meV than previously reported. A set of spectroscopic parameters for NCCN(+)(X(2)Pi(g)) has been calculated using high level ab initio calculations. The experimental spectra are found to consist of ionizing transitions populating the vibronic levels of NCCN(+), which consist of pure vibronic progressions, combination modes involving the symmetric CN stretch, the CC stretch, and even quanta of the antisymmetric CN stretch, and bending vibrations. These bands are identified with the guidance of the present ab initio calculations.     

Structure of the vinyldiazomethyl anion and energetic comparison to the cyclic isomers

The 351.1 nm photoelectron spectrum of the vinyldiazomethyl anion has been measured. The ion is generated through the reaction of the allyl anion with N(2)O in helium buffer gas in a flowing afterglow source. The spectrum exhibits the vibronic structure of the vinyldiazomethyl radical in its electronic ground state as well as in the first excited state. Electronic structure calculations have been performed for these molecules at the B3LYP/6-311++G(d,p) level of theory. A Franck-Condon simulation of the X (2)A' state portion of the spectrum has been carried out using the geometries and normal modes of the anion and radical obtained from these calculations. The simulation unambiguously shows that the ions predominantly have an E conformation. The electron affinity (EA) of the radical has been determined to be 1.864 +/- 0.007 eV. Vibrational frequencies of 185 +/- 10 and 415 +/- 20 cm(-1) observed in the spectrum have been identified as in-plane CCN bending and CCC bending modes, respectively, for the X (2)A' state. The spectrum for the A (2)A' state is broad and structureless, reflecting large geometry differences between the anion and the radical, particularly in the CCN angle, as well as vibronic coupling with the X (2)A' state. The DFT calculations have also been used to better understand the mechanism of the allyl anion reaction with N(2)O. Collision-induced dissociation of the structural isomer of the vinyldiazomethyl anion, the 1-pyrazolide ion, has been examined, and energetics of the structural isomers is discussed.     

Thermochemical studies of N-methylpyrazole and N-methylimidazole

The 351.1 nm photoelectron spectra of the N-methyl-5-pyrazolide anion and the N-methyl-5-imidazolide anion are reported. The photoelectron spectra of both isomers display extended vibrational progressions in the X2A' ground states of the corresponding radicals that are well reproduced by Franck-Condon simulations, based on the results of B3LYP/6-311++G(d,p) calculations. The electron affinities of the N-methyl-5-pyrazolyl radical and the N-methyl-5-imidazolyl radical are 2.054 +/- 0.006 eV and 1.987 +/- 0.008 eV, respectively. Broad vibronic features of the A(2)A' ' states are also observed in the spectra. The gas-phase acidities of N-methylpyrazole and N-methylimidazole are determined from measurements of proton-transfer rate constants using a flowing afterglow-selected ion flow tube instrument. The acidity of N-methylpyrazole is measured to be Delta(acid)G(298) = 376.9 +/- 0.7 kcal mol(-1) and Delta(acid)H(298) = 384.0 +/- 0.7 kcal mol(-1), whereas the acidity of N-methylimidazole is determined to be Delta(acid)G(298) = 380.2 +/- 1.0 kcal mol(-1) and Delta(acid)H(298)= 388.1 +/- 1.0 kcal mol(-1). The gas-phase acidities are combined with the electron affinities in a negative ion thermochemical cycle to determine the C5-H bond dissociation energies, D(0)(C5-H, N-methylpyrazole) = 116.4 +/- 0.7 kcal mol(-1) and D(0)(C5-H, N-methylimidazole) = 119.0 +/- 1.0 kcal mol(-1). The bond strengths reported here are consistent with previously reported bond strengths of pyrazole and imidazole; however, the error bars are significantly reduced.     

Spectroscopic characterization of the ground and low-lying electronic states of Ga2N via anion photoelectron spectroscopy

Anion photoelectron spectra of Ga(2)N(-) were measured at photodetachment wavelengths of 416 nm(2.978 eV), 355 nm(3.493 eV), and 266 nm(4.661 eV). Both field-free time-of-flight and velocity-map imaging methods were used to collect the data. The field-free time-of-flight data provided better resolution of the features, while the velocity-map-imaging data provided more accurate anisotropy parameters for the peaks. Transitions from the ground electronic state of the anion to two electronic states of the neutral were observed and analyzed with the aid of electronic structure calculations and Franck-Condon simulations. The ground-state band was assigned to a transition between linear ground states of Ga(2)N(-)(X (1)Sigma(g) (+)) and Ga(2)N(X (2)Sigma(u) (+)), yielding the electron affinity of Ga(2)N, 2.506+/-0.008 eV. Vibrationally resolved features in the ground-state band were assigned to symmetric and antisymmetric stretch modes of Ga(2)N, with the latter allowed by vibronic coupling to an excited electronic state. The energy of the observed excited neutral state agrees with that calculated for the A (2)Pi(u) state, but the congested nature of this band in the photoelectron spectrum is more consistent with a transition to a bent neutral state.     

Photoelectron spectroscopy of phosphorus hydride anions

Negative-ion photoelectron spectroscopy is applied to the PH-, PH2-, P2H-, P2H2-, and P2H3-molecular anions. Franck-Condon simulations of the photoelectron spectra are used to analyze the spectra and to identify various P2H(n)- species. The simulations employ density-functional theory calculations of molecular geometries and vibrational frequencies and normal modes, and coupled-cluster theory calculations of electron affinities. The following electron affinities are obtained: EA0(PH) = 1.027 +/- 0.006 eV, EA0(PH2) = 1.263 +/- 0.006 eV, and EA0(P2H) = 1.514 +/- 0.010 eV. A band is identified as a mixture of trans-HPPH- and cis-HPPH-. Although the trans and cis bands cannot be definitively assigned from experimental information, using theory as a guide we obtain EA0(trans-HPPH)= 1.00 +/- 0.01 eV and EA0(cis-HPPH) = 1.03 +/- 0.01 eV. A weak feature tentatively assigned to P2H3- has a vertical detachment energy of 1.74 eV. The derived gas-phase acidity of phosphine is delta(acid)G298(PH3) < or = 1509.7 +/- 2.1 kJ mo1(-1).     

Effects of alkyl substitution on the energetics of enolate anions and radicals.

The photoelectron spectra of the structural isomers of the three- and four-carbon enolate anions, n-C3H5O(-), i-C3H5O(-), n-C4H7O(-), s-C4H7O(-), and i-C4H7O(-) have been measured at 355 nm. Both the X(2A' ') ground and A(2A') first excited states of the corresponding radicals were accessed from the X(1A') ground state of the enolate anions. The separation energies of the ground and first excited states (T0) were determined: T0[(E)-n-C3H5O] = 1.19 +/- 0.02 eV, T0[(Z)-n-C3H5O] = 0.99 +/- 0.02 eV, T0[i-C3H5O] = 1.01 +/- 0.02 eV, T0[n-C4H7O] = 1.19 +/- 0.02 eV, T0[(2,3)-s-C4H7O] = 1.25 +/- 0.02 eV, T0[(1,2)-s-C4H7O] = 0.98 +/- 0.02 eV, and T0[i-C4H7O] = 1.36 +/- 0.02 eV. The effects of alkyl substitution on the vibronic structure and energetics previously observed in the vinoxy radical are discussed. The X(1A')-X(2A' ') relative stability is strongly influenced by substitution whereas the X(1A')-A(2A') relative stability remains nearly constant for all of the observed structural isomers. Alkyl substitution at the carbonyl carbon affects vibronic structure more profoundly than the energetics, while the converse is observed upon alkyl substitution at the alpha carbon.     

The band 12 issue in the electron momentum spectra of norbornane: a comparison with additional Green's Function calculations and ultraviolet photoemission measurements

In continuation of a recent study of the electronic structure of norbornane [J. Chem. Phys., 2004, 121, 10525] by means of electron momentum spectroscopy (EMS), we present Green's Function calculations of the ionization spectrum of this compound at the ADC(3) level using basis sets of varying quality, along with accurate evaluations at the CCSD(T) level of the vertical (26.5 eV) and adiabatic (22.1 eV) double ionization thresholds under C(2v) symmetry. The obtained results are compared with newly recorded ultraviolet photoemission spectra (UPS), up to binding energies of 40 eV. The theoretical predictions are entirely consistent with experiment and indicate that, in a vertical depiction of ionization, shake-up states at binding energies larger than approximately 26.5 eV tend to decay via emission of a second electron in the continuum. A band of s-type symmetry that has been previously seen at approximately 25 eV in the electron impact ionization spectra of norbornane is entirely missing in the UPS measurements and theoretical ADC(3) spectra. With regard to these results and to the time scales characterizing electron-electron interactions in EMS (10(-17) s) as compared with that (10(-13) s) of photon-electron interactions in UPS, and considering the p-type symmetry of the electron momentum distributions for the nearest 1b(1) and 1b(2) orbitals, this additional band can certainly not be due to adiabatic double ionization processes starting from the ground electronic state of norbornane, or to exceptionally strong vibronic coupling interactions between cationic states derived from ionization of the latter orbitals. It is therefore tentatively ascribed to autoionization processes via electronically excited and possibly dissociating states.     

Study of the valence wave function of thiophene with high resolution electron momentum spectroscopy and advanced Dyson orbital theories

Results of an exhaustive experimental study of the valence electronic structure of thiophene using high resolution electron momentum spectroscopy at impact energies of 1200 and 2400 eV are presented. The measurements were performed using an electron momentum spectrometer of the third generation at Tsinghua University, which enables energy, polar and azimuthal angular resolutions of the order of DeltaE = 0.8 eV, Deltatheta = +/-0.53 degrees and Deltaphi = +/-0.84 degrees . These measurements were interpreted by comparison with Green's function calculations of one-electron and shake-up ionization energies as well as of the related Dyson orbital electron momentum distributions, using the so-called third-order algebraic diagrammatic construction scheme (ADC(3)). Comparison of spherically averaged theoretical electron momentum distributions with experimental results very convincingly confirms the presence of two rather intense pi-2 pi*+1 shake-up lines at electron binding energies of 13.8 and 15.5 eV, with pole strengths equal to 0.18 and 0.13, respectively. Analysis of the electron momentum distributions associated with the two lowest 2A2 (pi3-1) and 2B1 (pi2-1) cationic states provides indirect evidence for a symmetry lowering and nuclear dynamical effects due to vibronic coupling interactions between these two states. ADC(3) Dyson orbital momentum distributions are systematically compared with distributions derived from Kohn-Sham (B3LYP) orbitals, and found to provide most generally superior insights into experiment.     

Mass-analyzed threshold ionization spectroscopy of pyridine. Structural distortion in the first excited state

For the first time, vibrational spectra of the pyridine cation in the electronic ground state have been measured via several intermediate states (0(0), 16b0(2), 16b0(4), 6a0(1), 6b(1), 16a0(1), 10a0(1) and 12(1)) by Mass-Analyzed Threshold Ionization (MATI) spectroscopy. From the MATI spectra, the adiabatic ionization energy of pyridine has been determined to be 74,185 +/- 6 cm(-1) (9.1978 +/- 0.0008 eV). Several vibronic modes in the ionic ground state could be assigned for the first time. An intensity gain of vibrations having b1 symmetry could be observed by activating the ion ground state. Also, a breakdown of the "delta nu = 0 propensity rule" for the excitation via the 16b(2) and 16b(4) states of the first excited states are displayed in the recorded spectra. In conjunction with ab initio calculations these observations can be explained by a strong geometrical distortion along the 16b vibration in the first excited state, leading to a "boat distortion".     

Negative electron binding energies observed in a triply charged anion: photoelectron spectroscopy of 1-hydroxy-3,6,8-pyrene-trisulfonate

We report the observation of negative electron binding energies (BEs) in a triply charged anion, 1-hydroxy-3,6,8-pyrene-trisulfonate (HPTS(3-)). Low-temperature photoelectron spectra were obtained for HPTS(3-) at several photon energies, revealing three detachment features below 0 electron BE. The HPTS(3-) trianion was measured to possess a negative BE of -0.66 eV. Despite the relatively high excess energy stored in HPTS(3-), it was observed to be a long-lived anion due to its high repulsive Coulomb barrier (RCB) ( approximately 3.3 eV), which prevents spontaneous electron emission. Theoretical calculations were carried out, which confirmed the negative electron BEs observed. The calculations further showed that the highest occupied molecular orbital in HPTS(3-) is an antibonding pi orbital on the pyrene rings, followed by lone pair electrons in the peripheral -SO(3) (-) groups. Negative electron BE is a unique feature of multiply charged anions due to the presence of the RCB. Such metastable species may be good models to study electron-electron and vibronic interactions in complex molecules.     

Nonadiabatic effects in the photoelectron spectrum of the pyrazolide-d3 anion: three-state interactions in the pyrazolyl-d3 radical

The 351.1 nm photoelectron spectrum of the 1-pyrazolide-d(3) anion has been measured. The photoelectron angular distributions indicate the presence of nearly degenerate electronic states of the 1-pyrazolyl-d(3) radical. Equation-of-motion ionization potential coupled-cluster singles and doubles (EOMIP-CCSD) calculations have been performed to study the low-lying electronic states. The calculations strongly suggest that three electronic states, energetically close to each other, are accessed in the photodetachment process. Strong interactions of the pseudo-Jahn-Teller type in each pair of the three states are evident in the calculations for the radical at the anion geometry. Model diabatic potentials of the three states have been constructed around the anion geometry in terms of the anion reduced normal coordinates up to the second order. An analytic method to parametrize the quadratic vibronic coupling (QVC) model potentials has been introduced. Parameters of the QVC model potentials have been determined from the EOMIP-CCSD and CCSD(T) calculations. Simulations of the 1-pyrazolide-d(3) spectrum have been performed with the model Hamiltonian, treating all vibronic interactions amongst the three states simultaneously. The simulation reproduces the fine structure of the observed spectrum very well, revealing complicated nonadiabatic effects in the low-lying states of the radical. The ground state of the 1-pyrazolyl-d(3) radical is (2)A(2) and the electron affinity is 2.935+/-0.006 eV. The first excited state is (2)B(1) with a term energy of 32+/-1 meV. While the high-symmetry (C(2v)) stationary points of the X (2)A(2) and A (2)B(1) states are minima, that of the state is a saddle point as a result of the pseudo-Jahn-Teller interactions with the other two states. The topology of the adiabatic potential energy surfaces is discussed.     

Vibrationally resolved photoelectron spectroscopy of BO- and BO2-: a joint experimental and theoretical study

We report a photoelectron spectroscopy and computational study of two simple boron oxide species: BO- and BO2-. Vibrationally resolved photoelectron spectra are obtained at several photon energies (355, 266, 193, and 157 nm) for the 10B isotopomers, 10BO- and 10BO2-. In the spectra of 10BO-, we observe transitions to the 2Sigma+ ground state and the 2Pi excited state of 10BO at an excitation energy of 2.96 eV. The electron affinity of 10BO is measured to be 2.510+/-0.015 eV. The vibrational frequencies of the ground states of 10BO- and 10BO and the 2Pi excited state are measured to be 1725+/-40, 1935+/-30, and 1320+/-40 cm-1, respectively. For 10BO2-, we observe transitions to the 2Pig ground state and two excited states of 10BO2, 2Piu, and 2Sigmau+, at excitation energies of 2.26 and 3.04 eV, respectively. The electron affinity of 10BO2 is measured to be 4.46+/-0.03 eV and the symmetrical stretching vibrational frequency of the 2Piu excited state of 10BO2 is measured to be 980+/-30 cm-1. Both density functional and ab initio calculations are performed to elucidate the electronic structure and chemical bonding of the two boron oxide molecules. Comparisons with the isoelectronic AlO- and AlO2- species and the closely related molecules CO, N2, CN-, and CO2 are also discussed.     

Norbornane: an investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green's function theories

We report on the results of an exhaustive study of the valence electronic structure of norbornane (C(7)H(12)), up to binding energies of 29 eV. Experimental electron momentum spectroscopy and theoretical Green's function and density functional theory approaches were all utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among all the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-zeta quality provides the best representation of the electron momentum distributions for all of the 20 valence orbitals of norbornane. This experimentally validated quantum chemistry model was then used to extract some chemically important properties of norbornane. When these calculated properties are compared to corresponding results from other independent measurements, generally good agreement is found. Green's function calculations with the aid of the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than 22.5 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet photoemission and newly presented (e,2e) ionization spectra, except for the band associated with the 1a(2) (-1) one-hole state, which is probably subject to rather significant vibronic coupling effects, and a band at approximately 25 eV characterized by a momentum distribution of "s-type" symmetry, which Green's function calculations fail to reproduce. We note the vicinity of the vertical double ionization threshold at approximately 26 eV.     

Negative ions of nitroethane and its clusters

Valence and dipole-bound negative ions of the nitroethane (NE) molecule and its clusters are studied using photoelectron spectroscopy (PES), Rydberg electron transfer (RET) techniques, and ab initio methods. Valence adiabatic electron affinities (EA(a)s) of NE, C(2)H(5)NO(2), and its clusters, (C(2)H(5)NO(2))(n), n=2-5, are estimated using vibrationally unresolved PES to be 0.3+/-0.2 eV (n=1), 0.9+/-0.2 eV (n=2), 1.5+/-0.2 eV (n=3), 1.9+/-0.2 eV (n=4), and 2.1+/-0.2 eV (n=5). These energies were then used to determine stepwise anion-neutral solvation energies and compared with previous literature values. Vertical detachment energies for (C(2)H(5)NO(2))(n)(-) were also measured to be 0.92+/-0.10 eV (n=1), 1.63+/-0.10 eV (n=2), 2.04+/-0.10 eV (n=3), and 2.3+/-0.1 eV (n=4). RET experiments show that Rydberg electrons can be attached to NE both as dipole-bound and valence bound anion states. The results are similar to those found for nitromethane (NM), where it was argued that the diffuse dipole state act as a "doorway state" to the more tightly bound valence anion. Using previous models for relating the maximum in the RET dependence of the Rydberg effective principle number n(max)(*), the dipole-bound electron affinity is predicted to be approximately 25 meV. However, a close examination of the RET cross section data for NE and a re-examination of such data for NM finds a much broader dependence on n(*) than is seen for RET in conventional dipole bound states and, more importantly, a pronounced [l] dependence is found in n(max)(*) (n(max)(*) increases with [l]). Ab initio calculations agree well with the experimental results apart from the vertical electron affinity value associated with the dipole bound state which is predicted to be 8 meV. Moreover, the calculations help to visualize the dramatic difference in the distributions of the excess electron for dipole-bound and valence states, and suggest that NE clusters form only anions where the excess electron localizes on a single monomer.     

Reactivity of titanium dimer and molecular nitrogen in rare gas matrices. Vibrational and electronic spectra and structure of Ti2N2

The reactivity of diatomic titanium with molecular nitrogen has been investigated in rare gas matrices. The formation of Ti2N2 from the condensation of effusive beams of Ti and N2 in neon and argon matrices is observed after sample deposition. Our results also show that the in situ formation results from the spontaneous reaction at 9 K of ground state Ti2 with N2. Several low-lying excited states of Ti2N2 are also observed between 0.78 and 1.1 eV above the ground state, leading to a complex sequence of interacting vibronic transitions, merging into a broad continuum above 1.25 eV. Observations of Ti2(14)N2, Ti2(15)N2 and Ti2(14)N(15)N isotopic data enable the determination of all fundamental vibrations in the ground electronic state. Semi-empirical harmonic potential calculations lead to estimates of 3.22 N cm(-1) for the Ti-N bond force constant and 90 +/- 5 degrees for the bond angles. Comparisons with TiN diatomic data suggest a near square-planar structure with 175 +/- 3 pm TiN bond distance. Quantum chemical calculations at various levels indicate a 1A(g) ground state with a Ti-N distance close to 180 pm and 89 degrees for the NTiN bond angle, and give fundamental frequencies in excellent agreement with the experimentally observed values. Further MRCI calculations on all low-lying states enable an interpretation of the complex electronic spectrum in the NIR region.     

Vibrational cooling in a cold ion trap: vibrationally resolved photoelectron spectroscopy of cold C60(-) anions

We demonstrate vibrational cooling of anions via collisions with a background gas in an ion trap attached to a cryogenically controlled cold head (10-400 K). Photoelectron spectra of vibrationally cold C60(-) anions, produced by electrospray ionization and cooled in the cold ion trap, have been obtained. Relative to spectra taken at room temperature, vibrational hot bands are completely eliminated, yielding well-resolved vibrational structures and a more accurate electron affinity for neutral C60. The electron affinity of C60 is measured to be 2.683+/-0.008 eV. The cold spectra reveal complicated vibrational structures for the transition to the C60 ground state due to the Jahn-Teller effect in the ground state of C60(-). Vibrational excitations in the two A(g) modes and eight H(g) modes are observed, providing ideal data to assess the vibronic couplings in C60(-).     

The Kohn-Sham density of states and band gap of water: from small clusters to liquid water

Electronic properties of water clusters (H2O)(n), with n=2, 4, 8, 10, 15, 20, and 30 molecules were investigated by sequential Monte Carlo/density-functional theory (DFT) calculations. DFT calculations were carried out over uncorrelated configurations generated by Monte Carlo simulations of liquid water with a reparametrized exchange-correlation functional that reproduces the experimental information on the electronic properties (first ionization energy and highest occupied molecular orbital-lowest unoccupied molecular orbital gap) of the water dimer. The dependence of electronic properties on the cluster size (n) shows that the density of states (DOS) of small water clusters (n>10) exhibits the same basic features that are typical of larger aggregates, such as the mixing of the 3a1 and 1b1 valence bands. When long-ranged polarization effects are taken into account by the introduction of embedding charges, the DOS associated with 3a1 orbitals is significantly enhanced. In agreement with valence-band photoelectron spectra of liquid water, the 1b1, 3a1, and 1b2 electron binding energies in water aggregates are redshifted by approximately 1 eV relative to the isolated molecule. By extrapolating the results for larger clusters the threshold energy for photoelectron emission is 9.6+/-0.15 eV (free clusters) and 10.58+/-0.10 eV (embedded clusters). Our results for the electron affinity (V0=-0.17+/-0.05 eV) and adiabatic band gap (E(G,Ad)=6.83+/-0.05 eV) of liquid water are in excellent agreement with recent information from theoretical and experimental works.     

High resolution and low-temperature photoelectron spectroscopy of an oxygen-linked fullerene dimer dianion: C(120)O(2-)

C(120)O comprises two C(60) cages linked by a furan ring and is formed by reactions of C(60)O and C(60). We have produced doubly charged anions of this fullerene dimer (C(120)O(2-)) and studied its electronic structure and stability using photoelectron spectroscopy and theoretical calculations. High resolution and vibrationally resolved photoelectron spectra were obtained at 70 K and at several photon energies. The second electron affinity of C(120)O was measured to be 1.02+/-0.03 eV and the intramolecular Coulomb repulsion was estimated to be about 0.8 eV in C(120)O(2-) on the basis of the observed repulsive Coulomb barrier. A low-lying excited state ((2)B(1)) was also observed for C(120)O(-) at 0.09 eV above the ground state ((2)A(1)). The C(120)O(2-) dianion can be viewed as a single electron on each C(60) ball very weakly coupled. Theoretical calculations showed that the singlet and triplet states of C(120)O(2-) are nearly degenerate and can both be present in the experiment. The computed electron binding energies and excitation energies, as well as Franck-Condon factors, are used to help interpret the photoelectron spectra. A C-C bond-cleaved isomer, C(60)-O-C(60) (2-), was also observed with a higher electron binding energy of 1.54 eV.