Ab initio calculations on low-lying electronic states of SnCl(2)- and Franck-Condon simulation of its photodetachment spectrum

Geometry optimization and harmonic vibrational frequency calculations have been carried out on low-lying doublet and quartet electronic states of stannous (tin(II)) dichloride anion (SnCl(2)(-)) employing the CASSCF and RCCSD(T) methods. The small-core fully-relativistic effective core potential, ECP28MDF, was used for Sn in these calculations, together with valence basis sets of up to augmented correlation-consistent polarized-valence quintuple-zeta (aug-cc-pV5Z) quality. The ground electronic state of SnCl(2)(-) is determined to be the X(2)B(1) state, with the A(2)B(2) and ?(4)Sigma state, calculated to be ca. 1.50 and 2.72 eV higher in energy respectively. The electron affinities of the X(1)A(1) and ?(3)B(1) states of SnCl(2) have been computed to be 1.568+/-0.007 and 4.458+/-0.002 eV respectively, including contributions of core correlation and extrapolation to the complete basis set limit. The SnCl(2) (X(1)A(1)) + e <-- SnCl(2)(-) (X(2)B(1)) and SnCl(2) (?(3)B(1)) + e <-- SnCl(2)(-) (X(2)B(1)) photodetachment bands have been simulated with computed Franck-Condon factors, which include an allowance for anharmonicity and Duschinsky rotation.     

Vibronic coupling in the superoxide anion: the vibrational dependence of the photoelectron angular distribution

We present a comprehensive photoelectron imaging study of the O(2)(X (3)Σ(g)(-),v(')=0-6)←O(2)(-)(X (2)Π(g),v(")=0) and O(2)(a?(1)Δ(g),v(')=0-4)←O(2)(-)(X (2)Π(g),v(")=0) photodetachment bands at wavelengths between 900 and 455 nm, examining the effect of vibronic coupling on the photoelectron angular distribution (PAD). This work extends the v(')=1-4 data for detachment into the ground electronic state, presented in a recent communication [R. Mabbs, F. Mbaiwa, J. Wei, M. Van Duzor, S. T. Gibson, S. J. Cavanagh, and B. R. Lewis, Phys. Rev. A 82, 011401(R) (2010)]. Measured vibronic intensities are compared to Franck-Condon predictions and used as supporting evidence of vibronic coupling. The results are analyzed within the context of the one-electron, zero core contribution (ZCC) model [R. M. Stehman and S. B. Woo, Phys. Rev. A 23, 2866 (1981)]. For both bands, the photoelectron anisotropy parameter variation with electron kinetic energy, β(E), displays the characteristics of photodetachment from a d-like orbital, consistent with the π(g)(?) 2p highest occupied molecular orbital of O(2)(-). However, differences exist between the β(E) trends for detachment into different vibrational levels of the X (3)Σ(g)(-) and a?(1)Δ(g) electronic states of O(2). The ZCC model invokes vibrational channel specific "detachment orbitals" and attributes this behavior to coupling of the electronic and nuclear motion in the parent anion. The spatial extent of the model detachment orbital is dependent on the final state of O(2): the higher the neutral vibrational excitation, the larger the electron binding energy. Although vibronic coupling is ignored in most theoretical treatments of PADs in the direct photodetachment of molecular anions, the present findings clearly show that it can be important. These results represent a benchmark data set for a relatively simple system, upon which to base rigorous tests of more sophisticated models.     

Vacuum ultraviolet photoionization of C3

Photoionization efficiency (PIE) curves for C(3) molecules produced by laser ablation are measured from 11.0 to 13.5 eV with tunable vacuum ultraviolet undulator radiation. A step in the PIE curve versus photon energy, obtained with N(2) as the carrier gas, supports the conclusion of very effective cooling of C(3) to its linear (1)Sigma(g)(+) ground state. The second step observed in the PIE curve versus photon energy could be the first experimental evidence of the C(3)(+)((2)Sigma(g)(+)) excited state. The experimental results, complemented by ab initio calculations, suggest a state-to-state vertical ionization energy of 11.70 +/- 0.05 eV between the C(3)(X(1)Sigma(g)(+)) and the C(3)(+)(X(2)Sigma(u)(+)) states. An ionization energy of 11.61 +/- 0.07 eV between the neutral and ionic ground states of C(3) is deduced using the data together with our calculations. Accurate ab initio calculations are performed for both linear and bent geometries on the lowest doublet electronic states of C(3)(+) using Configuration Interaction (CI) approaches and large basis sets. These calculations confirm that C(3)(+) is bent in its electronic ground state, which is separated by a small potential barrier from the (2)Sigma(u)(+) minimum. The gradual increase at the onset of the PIE curve suggests a geometry change between the ground neutral and cationic states. The energies between several doublet states of the ion are theoretically determined to be 0.81, 1.49, and 1.98 eV between the (2)Sigma(u)(+) and the (2)Sigma(g)(+),( 2)Pi(u), (2)Pi(g) excited states of C(3)(+), respectively.     

The visible spectrum of zirconium dioxide, ZrO2

The electronic spectrum of a cold molecular beam of zirconium dioxide, ZrO(2), has been investigated using laser induced fluorescence (LIF) in the region from 17,000 cm(-1) to 18,800 cm(-1) and by mass-resolved resonance enhanced multi-photon ionization (REMPI) spectroscopy from 17,000 cm(-1)-21,000 cm(-1). The LIF and REMPI spectra are assigned to progressions in the A?(1)B(2)(ν(1), ν(2), ν(3)) ← X?(1)A(1)(0, 0, 0) transitions. Dispersed fluorescence from 13 bands was recorded and analyzed to produce harmonic vibrational parameters for the X?(1)A(1) state of ω(1) = 898(1) cm(-1), ω(2) = 287(2) cm(-1), and ω(3) = 808(3) cm(-1). The observed transition frequencies of 45 bands in the LIF and REMPI spectra produce origin and harmonic vibrational parameters for the A?(1)B(2) state of T(e) = 16,307(8) cm(-1), ω(1) = 819(3) cm(-1), ω(2) = 149(3) cm(-1), and ω(3) = 518(4) cm(-1). The spectra were modeled using a normal coordinate analysis and Franck-Condon factor predictions. The structures, harmonic vibrational frequencies, and the potential energies as a function of bending angle for the A?(1)B(2) and X?(1)A(1) states are predicted using time-dependent density functional theory, complete active space self-consistent field, and related first-principle calculations. A comparison with isovalent TiO(2) is made.     

Communication: multistate quantum dynamics of photodissociation of carbon dioxide between 120 nm and 160 nm

UV absorption cross section of CO(2) is studied using high level ab initio quantum chemistry for electrons and iterative quantum dynamics for nuclear motion on interacting global full dimensional potential energy surfaces. Six electronic states-1, 2, 3(1)A(') and 1, 2, 3(1)A(")-are considered. At linearity, they correspond to the ground electronic state X?(1)Σ(g) (+) and the optically forbidden but vibronically allowed valence states 1(1)Δ(u), 1(1)Σ(u) (-), and 1(1)Π(g). In the Franck-Condon region, these states interact via Renner-Teller and conical intersections and are simultaneously involved in an intricate network of non-adiabatic couplings. The absorption spectrum, calculated for many rotational states, reproduces the distinct two-band shape of the experimental spectrum measured at 190 K and the characteristic patterns of the diffuse structures in each band. Quantum dynamics unravel the relative importance of different vibronic mechanisms, while metastable resonance states, underlying the diffuse structures, provide dynamically based vibronic assignments of individual lines.     

Multiconfigurational self-consistent field and multireference internally contracted configuration interaction studies on the excited states of weakly bonded NO2 dimer (N2O4)

In this paper, the vertical excitation energies of total of 32 states of N(2)O(4) including the lowest two singlet states and two triplet states of each of the A(g), B(3u), B(2u), B(1g), B(1u), B(2g), B(3g), and A(u) symmetries were calculated at multiconfigurational self-consistent field (MCSCF) and the multireference internally contracted configuration interaction (MRCI) levels of theory on the active space (15o,16e) with aug-cc-pVDZ basis set. The potential energy curves of the eight singlet states(1 (1)A(g), 1 (1)B(3u), 1 (1)B(2u), 1 (1)B(1g), 1 (1)B(1u), 1 (1)B(2g), 1 (1)B(3g), and 1 (1)A(u)) and eight triplet states (1 (3)A(g), 1 (3)B(3u), 1 (3)B(2u), 1 (3)B(1g), 1 (3)B(1u), 1 (3)B(2g), 1 (3)B(3g), and 1 (3)A(u)) were calculated at MCSCF and MRCI levels of theory on the active space (15o,16e) with aug-cc-pVDZ basis set along the N-N distance. The vertical excitation energies of 1 (1)B(3u), 1 (1)B(2u), and 1 (1)B(1u) states with nonzero transition moment are 4.60 eV (269.6 nm), 6.06 eV (204.6 nm), and 7.71 eV (160.8 nm), respectively, at MRCI level of theory. The photodissociation asymptotics were assigned as NO(2)(X (2)A(1))+NO(2)(X (2)A(1)) for ground state 1 (1)A(g) and the 1 (3)B(1u) state, NO(2)(X (2)A(1))+NO(2)(1 (2)A(2)) for the 1 (1)B(1g), 1 (3)B(1g), 1 (1)A(u), and 1 (3)A(u) states, NO(2)(X (2)A(1))+NO(2)(1 (2)B(1)) for the 1 (1)B(3u), 1 (3)B(3u), 1 (1)B(2g), and 1 (3)B(2g) states, and NO(2)(X (2)A(1))+NO(2)(1 (2)B(2)) for the 1 (1)B(2u), 1 (3)B(2u), 1 (1)B(3g), and 1 (3)B(3g) states.     

Gallium oxide and dioxide: investigation of the ground and low-lying electronic states via anion photoelectron spectroscopy

The GaO and GaO2 molecules were investigated using negative ion photoelectron spectroscopy. All the photoelectron spectra showed vibrationally resolved progressions. With the aid of electronic structure calculations and Franck-Condon spectral simulations, different molecular parameters and energetics of GaO-/GaO and GaO2-/GaO2 were determined, including the electron affinity of GaO, the vibrational frequency of GaO-, and the term energy, spin-orbit splitting, and vibrational frequency for the first excited A 2PiOmega state of GaO. The GaO2- photoelectron spectra comprised three bands assigned as transitions from the linear X 1Sigma(g)+ ground state of GaO2- to three linear neutral states: the A 2Pi(g), B 2Pi(u), and C 2Sigma(u) + states. The symmetric stretch frequencies of the anion and three neutral states as well as the spin-orbit splitting of the neutral 2Pi states were determined. Electronic structure calculations found the neutral lowest energy linear structure to be only 63 meV higher than the neutral bent geometry.     

The lowest singlet states of octatetraene revisited

The two lowest excited singlet states of all-trans-1,3,5,7-octatetraene, 2?(1)A(-)(g) and 1?(1)B(+)(u), are studied by means of high level ab initio methods computing the vertical and adiabatic excitation energies for both states and the vertical emission energy for the 1 (1)A(g)(-)←2?(1)A(-)(g) transition. The results confirm the known assignment of two energies, the 2?(1)A(-)(g) adiabatic excitation energy and the 2?(1)A(-)(g) vertical emission energy, for which well defined experimental values are available, with an excellent agreement between theory and experiment. In the experimental absorption spectrum, the maximum of the band describing the 1?(1)B(+)(u)←1?(1)A(g)(-) excitation is the first peak and it has been assigned to the (0-0) vibrational transition, but in literature it is normally compared with the theoretical vertical excitation energy. This comparison has been questioned in the past, but a conclusive demonstration of its lack of foundation has not been given. The analysis reported here, while confirming the assignment of the highest peak in the experimental spectrum to the (0-0) adiabatic transition, indicates that it cannot be used as a reference for the vertical excitation energy. The theoretical vertical excitation energies for the 2?(1)A(-)(g) and 1?(1)B(+)(u) states are found to be almost degenerate, with a value, ? 4.8 eV, higher than that normally accepted in the literature, 4.4 eV. The motivations which have induced in the past other authors to consider this a correct value are discussed and the origin of their feebleness are analyzed.     

Spectroscopic investigation of Al2N and its anion via negative ion photoelectron spectroscopy

Negative ion photoelectron spectroscopy was used to elucidate the electronic and geometric structure of the gaseous Al2N/Al2N- molecules, using photodetachment wavelengths of 416 nm (2.977 eV), 355 nm (3.493 eV), and 266 nm (4.661 eV). Three electronic bands are observed and assigned to the X2Sigma(u)+ <-- X1Sigma(g)+, A2Pi(u) <-- X1Sigma(g)+, and B2Sigma(g)+ <-- X1Sigma(g)+ electronic transitions, with the caveat that one or both excited states may be slightly bent. With the aid of density functional theory calculations and Franck-Condon spectral simulations, we determine the adiabatic electron affinity of Al2N, 2.571 +/- 0.008 eV, along with geometry changes upon photodetachment, vibrational frequencies, and excited-state term energies. Observation of excitation of the odd vibrational levels of the antisymmetric stretch (nu3) suggests a breakdown of the Franck-Condon approximation, caused by the vibronic coupling between the X2Sigma(u)+ and B2Sigma(g)+ electronic states through the nu3 mode.     

Electronic states and spin-orbit splitting of lanthanum dimer

Lanthanum dimer (La(2)) was studied by mass-analyzed threshold ionization (MATI) spectroscopy and a series of multi-configuration ab initio calculations. The MATI spectrum exhibits three band systems originating from ionization of the neutral ground electronic state, and each system shows vibrational frequencies of the neutral molecule and singly charged cation. The three ionization processes are La(2)(+) (a(2)∑(g)(+)) ← La(2) (X(1)∑(g)(+)), La(2)(+) (b(2)Π(3/2, u)) ← La(2) (X(1)∑(g)(+)), and La(2)(+) (b(2)Π(1/2, u)) ← La(2) (X(1)∑(g)(+)), with the ionization energies of 39,046, 40,314, and 40,864 cm(-1), respectively. The vibrational frequency of the X(1)Σ(g)(+) state is 207 cm(-1), and those of the a(2)Σ(g)(+), b(2)Π(3/2, u) and b(2)Π(1/2, u) are 235.7, 242.2, and 240 cm(-1). While X(1)Σ(g)(+) is the ground state of the neutral molecule, a(2)Σ(g (+) and b(2)Π(u) are calculated to be the excited states of the cation. The spin-orbit splitting in the b(2)Π(u) ion is 550 cm(-1). An X(4)Σ(g)(-) state of La(2)(+) was predicted by theory, but not observed by the experiment. The determination of a singlet ground state of La(2) shows that lanthanum behaves differently from scandium and yttrium.     

M-M bond-stretching energy landscapes for M2(dimen)4(2+) (M = Rh, Ir; dimen = 1,8-diisocyanomenthane) complexes

Isomers of Ir(2)(dimen)(4)(2+) (dimen = 1,8-diisocyanomenthane) exhibit different Ir-Ir bond distances in a 2:1 MTHF/EtCN solution (MTHF = 2-methyltetrahydrofuran). Variable-temperature absorption data suggest that the isomer with the shorter Ir-Ir distance is favored at room temperature [K = ～8; ΔH° = -0.8 kcal/mol; ΔS° = 1.44 cal mol(-1) K(-1)]. We report calculations that shed light on M(2)(dimen)(4)(2+) (M = Rh, Ir) structural differences: (1) metal-metal interaction favors short distances; (2) ligand deformational-strain energy favors long distances; (3) out-of-plane (A(2u)) distortion promotes twisting of the ligand backbone at short metal-metal separations. Calculated potential-energy surfaces reveal a double minimum for Ir(2)(dimen)(4)(2+) (～4.1 ? Ir-Ir with 0° twist angle and ～3.6 ? Ir-Ir with ±12° twist angle) but not for the rhodium analogue (～4.5 ? Rh-Rh with no twisting). Because both the ligand strain and A(2u) distortional energy are virtually identical for the two complexes, the strength of the metal-metal interaction is the determining factor. On the basis of the magnitude of this interaction, we obtain the following results: (1) a single-minimum (along the Ir-Ir coordinate), harmonic potential-energy surface for the triplet electronic excited state of Ir(2)(dimen)(4)(2+) (R(e,Ir-Ir) = 2.87 ?; F(Ir-Ir) = 0.99 mdyn ?(-1)); (2) a single-minimum, anharmonic surface for the ground state of Rh(2)(dimen)(4)(2+) (R(e,Rh-Rh) = 3.23 ?; F(Rh-Rh) = 0.09 mdyn ?(-1)); (3) a double-minimum (along the Ir-Ir coordinate) surface for the ground state of Ir(2)(dimen)(4)(2+) (R(e,Ir-Ir) = 3.23 ?; F(Ir-Ir) = 0.16 mdyn ?(-1)).     

The photodissociation of ozone in the Hartley band: a theoretical analysis

Three-dimensional diabatic potential energy surfaces for the lowest four electronic states of ozone with 1A' symmetry-termed X, A, B, and R-are constructed from electronic structure calculations. The diabatization is performed by reassigning corresponding energy points. Although approximate, these diabatic potential energy surfaces allow one to study the uv photodissociation of ozone on a level of theory not possible before. In the present work photoexcitation in the Hartley band and subsequent dissociation into the singlet channel, O3X+hnu-->O(1D)+O2(a 1Deltag), are investigated by means of quantum mechanical and classical trajectory calculations using the diabatic potential energy surface of the B state. The calculated low-resolution absorption spectrum as well as the vibrational and rotational state distributions of O2(a 1Deltag) are in good agreement with available experimental results.     

Mg2H2: new insight on the Mg-Mg bonding and spectroscopic study

The six dimensional potential energy surface of the electronic ground state X?(1)Σ(g)(+) of Mg(2)H(2) has been generated by the coupled-cluster approach with single, double and perturbative triple excitations [CCSD(T)] combined with the aug-cc-pCVTZ basis set for Mg atoms and the aug-cc-pVTZ basis set for the H atoms. The analytical representation of this surface was used in variational calculations of the rovibrational energies of Mg(2)H(2), Mg(2)D(2), and HMg(2)D for J = 0 and 1. For Mg(2)H(2), the rotational constant B(0) is computed to be 0.1438 cm(-1), and the fundamental anharmonic wavenumbers are calculated to be ν(1) = 1527.3 cm(-1) (Σ(g)(+)), ν(2) = 275.3 cm(-1) (Σ(g)(+)), ν(3) = 1503.6 cm(-1) (Σ(u)(+)), ν(4) = 312.9 cm(-1) (Π(g)), and ν(5) = 256.5 cm(-1) (Π(u)). In addition, the electronic ground states of Mg(2)H, MgH(2), Mg(2), and MgH have been investigated in order to compute the bonding energies of Mg(2)H(2) and to explain the strength of the Mg-Mg bond in this tetra-atomic molecule. The nature of the low-lying excited states of Mg(2)H(2) is also studied.     

Broken-symmetry unrestricted hybrid density functional calculations on nickel dimer and nickel hydride

In the present work we investigate the adequacy of broken-symmetry unrestricted density functional theory for constructing the potential energy curve of nickel dimer and nickel hydride, as a model for larger bare and hydrogenated nickel cluster calculations. We use three hybrid functionals: the popular B3LYP, Becke's newest optimized functional Becke98, and the simple FSLYP functional (50% Hartree-Fock and 50% Slater exchange and LYP gradient-corrected correlation functional) with two basis sets: all-electron (AE) Wachters+f basis set and Stuttgart RSC effective core potential (ECP) and basis set. We find that, overall, the best agreement with experiment, comparable to that of the high-level CASPT2, is obtained with B3LYP/AE, closely followed by Becke98/AE and Becke98/ECP. FSLYP/AE and B3LYP/ECP give slightly worse agreement with experiment, and FSLYP/ECP is the only method among the ones we studied that gives an unacceptably large error, underestimating the dissociation energy of Ni(2) by 28%, and being in the largest disagreement with the experiment and the other theoretical predictions. We also find that for Ni(2), the spin projection for the broken-symmetry unrestricted singlet states changes the ordering of the states, but the splittings are less than 10 meV. All our calculations predict a deltadelta-hole ground state for Ni(2) and delta-hole ground state for NiH. Upon spin projection of the singlet state of Ni(2), almost all of our calculations: Becke98 and FSLYP both AE and ECP and B3LYP/AE predict (1)(d(A)(x(2)-y(2)d(B)(x(2)-y(2)) or (1)(d(A)(xy) (d)(B)(xy)) ground state, which is a mixture of (1)Sigma(g) (+) and (1)Gamma(g). B3LYP/ECP predicts a (3)(d(A)(x(2)-y(2))d(B)(xy) (mixture of (3)Sigma(g) (-) and (3)Gamma(u)) ground state virtually degenerate with the (1)(d(A)(x(2)-y(2)d(B)(x)(2)-y(2)/(1)(d(A)(xy)D(B)(xy) state. The doublet delta-hole ground state of NiH predicted by all our calculations is in agreement with the experimentally predicted (2)Delta ground state. For Ni(2), all our results are consistent with the experimentally predicted ground state of 0(g) (+) (a mixture of (1)Sigma(g) (+) and (3)Sigma(g) (-)) or 0(u) (-) (a mixture of (1)Sigma(u) (-) and (3)Sigma(u) (+)).     

The C-H bond dissociation energy of furan: photoelectron spectroscopy of the furanide anion

Using photoelectron spectroscopy, we interrogate the cyclic furanide anion (C(4)H(3)O(-)) to determine the electron affinity and vibrational structure of the neutral furanyl radical and the term energy of its first excited electronic state. We present the 364-nm photoelectron spectrum of the furanide anion and measure the electron affinity of the X?(2)A(') ground state of the α-furanyl radical to be 1.853(4) eV. A Franck-Condon analysis of the well-resolved spectrum allows determination of the harmonic frequencies of three of the most active vibrational modes upon X?(2)A(') ← X?(1)A(') photodetachment: 855(25), 1064(25), and 1307(40) cm(-1). These modes are ring deformation vibrations, consistent with the intuitive picture of furanide anion photodetachment, where the excess electron is strongly localized on the α-carbon atom. In addition, the A?(2)A(') excited state of the α-furanyl radical is observed 0.68(7) eV higher in energy than the X?(2)A(') ground state. Through a thermochemical cycle involving the known gas-phase acidity of furan, the electron affinity of the furanyl radical yields the first experimental determination of the C-H(α) bond dissociation energy of furan (DH(298)(C(4)H(3)O-H(α))): 119.8(2) kcal mol(-1).     

Variation of radiative lifetimes of NH2(Ã2A1) with rotational levels in the (0, 8, 0) and (0, 9, 0) vibration bands

Radiative lifetimes from the first electronically excited state of the amidogen free radical, NH(2)(A?(2)A(1)), are reported for rotational states in selected vibrational levels ν(2)' using laser-induced fluorescence. Thermal collision of argon, Ar(?)((3)P(0), (3)P(2)) metastable atoms in a microwave discharge-flow system with ammonia (NH(3)) molecules produced ground state NH(2)(X?(2)B(1)). The radiative lifetimes for the deactivation of NH(2)(A?(2)A(1)) were determined by measuring the decay profiles of NH(2)(A?(2)A(1)?→?X?(2)B(1)). In addition to the Fermi resonances with the ground state that lengthen the radiative lifetimes, a systematic increase in the radiative lifetimes with rotational quantum number was observed. Furthermore, the average radiative lifetimes of the (0, 9, 0) Γ, τ(1) = 18.65 ± 0.47 μs and (0, 8, 0) Φ, τ(2) = 23.72 ± 0.65 μs levels were much longer than those of the (0, 9, 0) Σ, τ(3) = 10.62 ± 0.47 μs, and (0, 8, 0) Π, τ(4) = 13.55 ± 0.55 μs states suggesting increased mixing of the first electronic excited and the ground states.     

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.     

1 + 1] photodissociation of CS(2)(+)(X̃2Π(g)) via the vibrationally mediated B̃2Σ(u)+ state: multichannels exhibiting and mode specific dynamics

Dissociation dynamics of CS(2)(+) vibrationally mediated via its B?(2)Σ(u)(+) state, was studied using the time-sliced velocity map imaging technique. The parent CS(2)(+) cation was prepared in its X?(2)Π(g) ground state through a [3 + 1] resonance enhanced multiphoton ionization process, via the 4pσ(3)Π(u) intermediate Rydberg state of neutral CS(2) molecule at 483.14 nm. CS(2)(+)(X?(2)Π(g)) was dissociated by a [1?+?1] photoexcitation mediated via the vibrationally selected B? state over a wavelength range of 267-283 nm. At these wavelengths the C?(2)Σ(g)(+) and D?(2)Σ(u)(+) states are excited, followed by numerous S(+) and CS(+) dissociation channels. The S(+) channels specified as three distinct regions were shown with vibrationally resolved structures, in contrast to the less-resolved structures being presented in the CS(+) channels. The average translational energy releases were obtained, and the S(+)∕CS(+) branching ratios with mode specificity were measured. Two types of dissociation mechanisms are proposed. One mechanism is the direct coupling of the C? and D? states with the repulsive satellite states leading to the fast photofragmentation. The other mechanism is the internal conversion of the C? and D? states to the B? state, followed by the slow fragmentation occurred via the coupling with the repulsive satellite states.     

New view of the ICN A continuum using photoelectron spectroscopy of ICN-

Negative-ion photoelectron spectroscopy of ICN(-) (X??(2)Σ(+)) reveals transitions to the ground electronic state (X??(1)Σ(+)) of ICN as well as the first five excited states ((3)Π(2), (3)Π(1), Π(0(-) ) (3), Π(0(+) ) (3), and (1)Π(1)) that make up the ICN A continuum. By starting from the equilibrium geometry of the anion, photoelectron spectroscopy characterizes the electronic structure of ICN at an elongated I-C bond length of 2.65 A?. Because of this bond elongation, the lowest three excited states of ICN ((3)Π(2), (3)Π(1), and Π(0(-) ) (3)) are resolved for the first time in the photoelectron spectrum. In addition, the spectrum has a structured peak that arises from the frequently studied conical intersection between the Π(0(+) ) (3) and (1)Π(1) states. The assignment of the spectrum is aided by MR-SO-CISD calculations of the potential energy surfaces for the anion and neutral ICN electronic states, along with calculations of the vibrational levels supported by these states. Through thermochemical cycles involving spectrally narrow transitions to the excited states of ICN, we determine the electron affinity, EA(ICN), to be 1.34(5) (+0.04∕-0.02) eV and the anion dissociation energy, D(0)(X??(2)Σ(+) I-CN(-)), to be 0.83 (+0.04/-0.02) eV.