Fluorescence excitation spectra of the b (1)Pi(u), b(') (1)Sigma(u) (+), c(n) (1)Pi(u), and c(n) (') (1)Sigma(u) (+) states of N(2) in the 80-100 nm region

Fluorescence excitation spectra produced through photoexcitation of N(2) using synchrotron radiation in the spectral region between 80 and 100 nm have been studied. Two broadband detectors were employed to simultaneously monitor fluorescence in the 115-320 nm and 300-700 nm regions, respectively. The peaks in the vacuum ultraviolet fluorescence excitation spectra are found to correspond to excitation of absorption transitions from the ground electronic state to the b (1)Pi(u), b(') (1)Sigma(u) (+), c(n) (1)Pi(u) (with n=4-8), c(n) (') (1)Sigma(u) (+) (with n=5-9), and c(4) (')(v('))(1)Sigma(u) (+) (with v(')=0-8) states of N(2). The relative fluorescence production cross sections for the observed peaks are determined. No fluorescence has been produced through excitation of the most dominating absorption features of the b-X transition except for the (1,0), (5,0), (6,0), and (7,0) bands, in excellent agreement with recent lifetime measurements and theoretical calculations. Fluorescence peaks, which correlate with the long vibrational progressions of the c(4) (') (1)Sigma(u) (+) (with v(')=0-8) and the b(') (1)Sigma(u) (+) (with v(') up to 19), have been observed. The present results provide important information for further unraveling of complicated and intriguing interactions among the excited electronic states of N(2). Furthermore, solar photon excitation of N(2) leading to the production of c(4) (')(0) may provide useful data required for evaluating and analyzing dayglow models relevant to the interpretation of c(4) (')(0) in the atmospheres of Earth, Jupiter, Saturn, Titan, and Triton.     

Solvent-mediated charge redistribution in photodissociation of IBr(-) and IBr(-)(CO2)

A combined experimental and theoretical investigation of photodissociation dynamics of IBr(-) and IBr(-)(CO(2)) on the B ((2)Σ(1/2)(+)) excited electronic state is presented. Time-resolved photoelectron spectroscopy reveals that in bare IBr(-) prompt dissociation forms exclusively I? + Br(-). Compared to earlier dissociation studies of IBr(-) excited to the A' ((2)Π(1∕2)) state, the signal rise is delayed by 200 ± 20 fs. In the case of IBr(-)(CO(2)), the product distribution shows the existence of a second major (～40%) dissociation pathway, Br? + I(-). In contrast to the primary product channel, the signal rise associated with this pathway shows only a 50 ± 20 fs delay. The altered product branching ratio indicates that the presence of one solvent-like CO(2) molecule dramatically affects the electronic structure of the dissociating IBr(-). We explore the origins of this phenomenon with classical trajectories, quantum wave packet studies, and MR-SO-CISD calculations of the six lowest-energy electronic states of IBr(-) and 36 lowest-energy states of IBr. We find that the CO(2) molecule provides sufficient solvation energy to bring the initially excited state close in energy to a lower-lying state. The splitting between these states and the time at which the crossing takes place depend on the location of the solvating CO(2) molecule.     

High resolution vacuum ultraviolet emission spectrum of D(2) from 78 to 103 nm: The D (1)Pi(u)-->X (1)Sigma(g) (+) and D(') (1)Pi(u) (-)-->X (1)Sigma(g) (+) band systems

The emission spectrum of the D(2) molecule has been studied at high resolution in the vacuum ultraviolet region 78.5-102.7 nm. A detailed analysis of the two D (1)Pi(u)-->X (1)Sigma(g) (+) and D(') (1)Pi(u) (-)-->X (1)Sigma(g) (+) electronic band systems is reported. New and improved values of the level energies of the two upper states have been derived with the help of the program IDEN [V. I. Azarov, Phys. Scr. 44, 528 (1991); 48, 656 (1993)], originally developed for atomic spectral analysis. A detailed comparison is made between the observed energy levels and solutions of coupled equations using the newest ab initio potentials by Wolniewicz and co-workers [J. Chem. Phys. 103, 1792 (1995); 99, 1851 (1993); J. Mol. Spectros. 212, 208 (2002); 220, 45 (2003)] taking into account the nonadiabatic coupling terms for the D (1)Pi(u) state with the lowest electronic states B (1)Sigma(u) (+), C (1)Pi(u), and B(') (1)Sigma(u) (+). A satisfactory agreement has been found for most of the level energies belonging to the D and D(') states. The remaining differences between observation and theory are probably due to nonadiabatic couplings with other higher electronic states which were neglected in the calculations.     

Study on the photodissociation spectra of CS2+ via B2Sigma u+ and C2Sigma g+ electronic states

The photodissociation spectra of CS(2)(+) ions via B(2)Sigma(u)(+) and C(2)Sigma(g)(+) electronic states have been studied by using two-photon excitation, where the parent CS(2)(+) ions were prepared by [3 + 1] REMPI (resonance-enhanced multiphoton ionization) at 483.2 nm from the jet-cooled CS(2) molecules. The [1 + 1] photodissociation spectrum of CS(2)(+) via the B(2)Sigma(u)(+)(upsilon(1)upsilon(2)0) <-- X(2)Pi(g,3/2)(000) transition was obtained by scanning the dissociation laser in the wavelength range of 270-285 nm and detecting the signal of both S(+) and CS(+). The [1 + 1'] photodissociation spectra of CS(2)(+) were obtained by fixing the first dissociation laser at 281.94 or 277.15 nm to excite the B(2)Sigma(u)(+) (000 or 100) <-- X(2)Pi(g,3/2)(000) transitions and scanning the second dissociation laser in the range of 606-763 nm to excite C(2)Sigma(g)(+)(upsilon(1)upsilon(2)0) <-- B(2)Sigma(u)(+)(000,100) transitions. New spectroscopic constants of nu(1) = 666.2 +/- 2.5 cm(-1), nu(2) = 363.2 +/- 1.9 cm(-1), chi(11) = -5.5 +/- 0.1 cm(-1), chi(22) = 1.6 +/- 0.1 cm(-1), chi(12) = -8.6 +/- 0.2 cm(-1), and k(122) = 44.9 +/- 2.5 cm(-1) (Fermi resonance constant) for the C(2)Sigma(g)(+) state are deduced from the [1 + 1'] photodissociation spectra. On the basis of the [1 + 1] and [1 + 1'] photodissociation spectra, the wavelength and level dependence of the product branching ratios CS(+)/S(+) has been found and the dissociation dynamics of CS(2)(+) ions via B(2)Sigma(u)(+) and C(2)Sigma(g)(+) electronic states are discussed.     

Gas phase electronic spectrum of linear AlCCH

The electronic spectrum of the aluminium containing species AlCCH has been detected in the gas phase in the region 315-355 nm. The experiment used a mass selective resonant two-color two-photon ionization technique coupled to a laser ablation source. Structures of the AlCCH isomers have been optimized using density functional theory (DFT) and the excitation energies to the low-lying electronic excited states calculated. Based on the analysis of the observed rotational structure and the theoretical data, the spectrum is assigned to the A (1)Pi<-- X (1)Sigma(+) electronic transition of linear AlCCH. The vibronic band system is complicated by the Renner-Teller effect in the excited state. The assignment yields nu(4)' = 516.4 cm(-1) for the stretching mode in the ground X (1)Sigma(+) state and nu(4)' = 654.5 cm(-1) for A (1)Pi excited state. Molecular constants determined from the rotational analysis are B(0)' = 0.16487(14), B(0)' = 0.17845(13) and T(0) = 28 755.04 cm(-1). The experimental and theoretical data indicate a shorter Al-C bond in the A (1)Pi excited than the X (1)Sigma(+) ground state.     

The d (3)Pi(g)-c (3)Sigma(u) (+) band system of C2

A two-dimensional fluorescence (excitation/emission) spectrum of C2 produced in an acetylene discharge was used to identify and separate emission bands from the d (3)Pi(g)<--c (3)Sigma(u) (+) and d (3)Pi(g)<--a (3)Pi(u) excitations. Rotationally resolved excitation spectra of the (4<--1), (5<--1), (5<--2), and (7<--3) bands in the d (3)Pi(g)<--c (3)Sigma(u) (+) system of C2 were observed by laser-induced fluorescence spectroscopy. The molecular constants of each vibrational level, determined from rotational analysis, were used to calculate the spectroscopic constants of the c (3)Sigma(u) (+) state. The principal molecular constants for the c (3)Sigma(u) (+) state are B(e)=1.9319(19) cm(-1), alpha(e)=0.018 55(69) cm(-1), omega(e)=2061.9 cm(-1), omega(e)x(e)=14.84 cm(-1), and T(0)(c-a)=8662.925(3) cm(-1). We report also the first experimental observations of dispersed fluorescence from the d (3)Pi(g) state to the c (3)Sigma(u) (+) state, namely, d (3)Pi(g)(v=3)-->c (3)Sigma(u) (+)(v=0,1).     

Intense-field modulation of NO2 multiphoton dissociation dynamics

We report on the dynamics of multiphoton excitation and dissociation of NO(2) at wavelengths between 395 and 420 nm and intensities between 4 and 10 TW cm(-2). The breakup of the molecule is monitored by NO A (2)Sigma(+)n(')=1,0-->X (2)Pi(r)n(")=0 fluorescence as a function of time delay between the driving field and a probe field which depletes the emission. It is found that generation of n(')=0 and 1 NO A (2)Sigma(+) results in different fluorescence modulation patterns due to the intense probe field. The dissociation dynamics are interpreted in terms of nuclear motions over light-induced potentials formed by coupling of NO(2) valence and Rydberg states to the applied field. Based on this model, it is argued that the time and intensity dependences of A (2)Sigma(+)n(')=0-->X (2)Pi(r)n(")=0 fluorescence are consistent with delayed generation of NO A (2)Sigma(+)n(')=0 via a light-induced bond-hardening brought about by the transient coupling of the dressed A (2)B(2) and Rydberg 3ssigma (2)Sigma(g) (+) states of the parent molecule. The increasingly prompt decay of A (2)Sigma(+)n(')=1-->X (2)Pi(r)n(")=0 fluorescence with increasing intensity, on the other hand, is consistent with a direct surface crossing between the X (2)A(1) and 3ssigma (2)Sigma(g) (+) dressed states to generate vibrationally excited products.     

A velocity map imaging study of the one and two photon dissociations of state-selected DCl+ cations

DCl(+)(X (2)Pi(32),v(+")=0) cations have been prepared by 2+1 resonance enhanced multiphoton ionization, and their subsequent fragmentation following excitation at numerous wavelengths in the range of 240-350 nm studied by velocity map imaging of the resulting Cl(+) products. This range of excitation wavelengths allows selective population of A (2)Sigma(+) state levels with all vibrational (v(+')) quantum numbers in the range 0< or =v(+')< or =15. Image analysis yields wavelength dependent branching ratios and recoil anisotropies of the various D+Cl(+) ((3)P(J), (1)D, and (1)S) product channels. Levels with 10< or =v(+')< or =15 have sufficient energy to predissociate, forming D+Cl(+)((3)P(J)) products with perpendicular recoil anisotropies-consistent with the A (2)Sigma(+)<--X (2)Pi parent excitation and subsequent fragmentation on a time scale that is fast compared with the parent rotational period. Branching into the various spin-orbit states of the Cl(+)((3)P(J)) product is found to depend sensitively upon v(+') and, in the case of the v(+')=13 level, to vary with the precise choice of excitation wavelength within the A (2)Sigma(+)<--X (2)Pi(13,0) band. Such variations have been rationalized qualitatively in terms of the differing contributions made to the overall predissociation rate of DCl(+)(A,v(+')) molecules by coupling to repulsive states of (4)Pi, (4)Sigma(-), and (2)Sigma(-) symmetries, all of which are calculated to cross the outer limb of the A (2)Sigma(+) state potential at energies close to that of the v(+')=10 level. Cl(+)((3)P(J)) fragments are detected weakly following excitation to A (2)Sigma(+) state levels with v(+')=0 or 1, Cl(+)((1)D) fragments dominate the ion yield when exciting via 2< or =v(+')< or =6 and via v(+')=9, while Cl(+)((1)S) fragments dominate the Cl(+) images obtained when exciting via levels with v(+')=7 and 8. Analysis of wavelength resolved action spectra for forming these Cl(+) ions and of the resulting Cl(+) ion images shows that (i) these ions all arise via two photon absorption processes, resonance enhanced at the one photon energy by the various A(v(+')<10) levels, (ii) the first A (2)Sigma(+)<--X (2)Pi absorption step is saturated under the conditions required to observe significant two photon dissociation, and (iii) the final absorption step from the resonance enhancing A(v(+')) level involves a parallel transition.     

Experimental and theoretical study of the electronic spectrum of BeAl

The electronic structure of BeAl was investigated by laser induced fluorescence and resonance enhanced multiphoton ionization spectroscopy. BeAl was formed by pulsed laser ablation of a Be/Al alloy in the presence of helium carrier gas, followed by a free jet expansion into vacuum. In agreement with recent ab initio studies, the molecule was found to have a (2)Pi(1/2) ground state. Transitions to two low lying electronic states, (2)(2)Pi(1/2)(v') <-- X (2)Pi(1/2) (v' = 0) and (1)(2)Delta(v') <-- X (2)Pi(1/2) (v' = 0,1), were observed and rotationally analyzed. An additional band system, identified as (4)(2)Sigma(+)(v') <-- X (2)Pi(1/2), was found in the 28 000-30 100 cm(-1) energy range. This transition exhibited an unusual pattern of vibrational levels resulting from an avoided crossing with the (5)(2)Sigma(+) electronic state. New multi-reference configuration interaction calculations were carried out to facilitate the interpretation of the UV bands.An ionization energy of 48 124(80) cm(-1) was determined for BeAl from photoionization efficiency (PIE) measurements. Fine structure in the PIE curve was attributed to resonances with Rydberg series correlating with vibrationally excited states of the BeAl(+) ion. Analysis of this structure yielded a vibrational frequency of 240(20) cm(-1) for the cation.     

Ab initio investigation of potential energy curves of the 23 electronic states of IBr correlating to neutral (2)P atoms

Potential energy surfaces for all Born-Oppenheimer electronic states of IBr molecule correlating to the neutral (2)P ((2)P(3/2) and (2)P(1/2)) iodine and bromine are calculated for the first time. Electric dipole and polarizability curves (static and transition) are also determined. Calculations include scalar and spin-orbit relativistic effects within all-electron Douglas-Kroll two-component Hamiltonian. Electron correlation is treated with quasi-degenerate multi-reference second-order perturbation theory. Seven adiabatic electronic states (X (1)Sigma(+), A'(3)Pi(2), A (3)Pi(1), 1 (3)Pi(0-), B (3)Pi(0+), B'(3)Sigma, and 2 (3)Pi(0+)) exhibit significant covalent bonding, and can support vibrational states. Calculated spectroscopic parameters agree with experiment to better than 1000 cm(-1) (T(e)), 10 cm(-1) (omega(e)), and 0.05 Angstrom (r(e)). A new 1 (3)Pi(0-) state correlating to ground-state atoms is predicted at T(e) approximately 14 000 cm(-1), omega(e) approximately 80 cm(-1), and r(e) approximately 3.0 Angstrom. The second new state (2 (3)Pi(0+)) correlates to excited iodine atom, with T(e) approximately 20 000 cm(-1), omega(e) approximately 115 cm(-1), and r(e) approximately 3.3 Angstrom. Non-adiabatic coupling parameters are calculated for the four avoided crossings, which arise due to electronic spin-orbit interaction. Estimated parameters of the B (3)Pi(0+)/B'(3)Sigma crossing (R(c) approximately 3.32 Angstrom; V approximately 120 cm(-1)) agree with experimental values. The previously unsuspected 2 (3)Pi(0-)/1 (1)Sigma(-) crossing of two repulsive surfaces provides a new collisional deactivation channel for Br* atoms at relative velocities above 1000 m s(-1). Several repulsive states (including 1 (1)Pi(1) and 2 (3)Pi(1)) intersect the B/B' system near the avoided crossing point, and may affect dynamics of IBr in strong laser fields.     

1 Pi<--X1 Sigma+ band systems of jet-cooled ScCo and YCo

Rotationally resolved resonant two-photon ionization (R2PI) spectra of ScCo and YCo are reported. The measured spectra reveal that these molecules possess ground electronic states of (1)Sigma(+) symmetry, as previously found in the isoelectronic Cr(2) and CrMo molecules. The ground state rotational constants for ScCo and YCo are B(0)(")=0.201 31(22) cm(-1) and B(0) (")=0.120 96(10) cm(-1), corresponding to ground state bond lengths of r(0) (")=1.812 1(10) A and r(0) (")=1.983 0(8) A, respectively. A single electronic band system, assigned as a (1)Pi<--X (1)Sigma(+) transition, has been identified in both molecules. In ScCo, the (1)Pi state is characterized by T(0)=15,428.8, omega(e)(')=246.7, and omega(e)(')x(e)(')=0.73 cm(-1). In YCo, the (1)Pi state has T(0)=13 951.3, omega(e)(')=231.3, and omega(e)(')x(e) (')=2.27 cm(-1). For YCo, hot bands originating from levels up to v(")=3 are observed, allowing the ground state vibrational constants omega(e)(")=369.8, omega(e)(")x(e)(")=1.47, and Delta G(12)(")=365.7 cm(-1) to be deduced. The bond energy of ScCo has been measured as 2.45 eV from the onset of predissociation in a congested vibronic spectrum. A comparison of the chemical bonding in these molecules to related molecules is presented.     

Observation of the d3Pi(g)<--c3Sigma(u)+ band system of C2

A new band system of C(2), d (3)Pi(g)<--c (3)Sigma(u) (+) is observed by laser induced fluorescence spectroscopy, constituting the first direct detection of the c (3)Sigma(u) (+) state of C(2). Observations were made by laser excitation of c (3)Sigma(u) (+)(v(")=0) C(2), produced in an acetylene discharge, to the d (3)Pi(g)(v(')=3) level, followed by detection of Swan band fluorescence. Rotational analysis of this band yielded rotational constants for the c (3)Sigma(u) (+)(v(")=0) state: B(0)=1.9218(2) cm(-1), lambda(0)=-0.335(4) cm(-1) and gamma(0)=0.011(2) cm(-1). The vibrational band origin was determined to be nu(3-0)=15861.28 cm(-1).     

Time-resolved study of solvent-induced recombination in photodissociated IBr-(CO2)n clusters

We report the time-resolved recombination of photodissociated IBr-(CO2)n (n = 5-10) clusters following excitation to the dissociative IBr-A' 2Pi12 state of the chromophore via a 180 fs, 795 nm laser pulse. Dissociation from the A' state of the bare anion results in I- and Br products. Upon solvation with CO2, the IBr- chromophore regains near-IR absorption only after recombination and vibrational relaxation on the ground electronic state. The recombination time was determined by using a delayed femtosecond probe laser, at the same wavelength as the pump, and detecting ionic photoproducts of the recombined IBr- cluster ions. In sharp contrast to previous studies involving solvated I2-, the observed recombination times for IBr-(CO2)n increase dramatically with increasing cluster size, from 12 ps for n = 5 to 900 ps for n = 8,10. The nanosecond recombination times are especially surprising in that the overall recombination probability for these cluster ions is unity. Over the range of 5-10 solvent molecules, calculations show that the solvent is very asymmetrically distributed, localized around the Br end of the IBr- chromophore. It is proposed that this asymmetric solvation delays the recombination of the dissociating IBr-, in part through a solvent-induced well in the A' state that (for n = 8,10) traps the evolving complex. Extensive electronic structure calculations and nonadiabatic molecular dynamics simulations provide a framework to understand this unexpected behavior.     

Dissociation of the OCS+ ion in low-lying electronic states studied using multiconfiguration second-order perturbation theory

Complete active space self-consistent-field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with atomic natural orbital basis sets were performed to investigate the S-loss direct dissociation of the 1 2Pi(X 2Pi), 2 2Pi(A 2Pi), 1 2Sigma+(B 2Sigma+), 1 4Sigma-, 1 2Sigma-, and 1 2Delta states of the OCS+ ion and the predissociations of the 1 2Pi, 2 2Pi, and 1 2Sigma+ states. Our calculations indicate that the S-loss dissociation products of the OCS(+) ion in the six states are the ground-state CO molecule plus the S+ ion in different electronic states. The CASPT2//CASSCF potential energy curves were calculated for the S-loss dissociation from the six states. The calculations indicate that the dissociation of the 1 4Sigma- state leads to the CO + S+ (4Su) products representing the first dissociation limit; the dissociations of the 1 2Pi, 1 2Sigma-, and 1 2Delta states lead to the CO + S+(2Du) products representing the second dissociation limit; and the dissociations of the 2 2Pi and 1 2Sigma+ states lead to the CO + S+(2Pu) products representing the third dissociation limit. Seams of the 1 2Pi-1 4Sigma-, 2 2Pi-1 4Sigma-, 2 2Pi-1 2Sigma-, 2 2Pi-1 2Delta, and 1 2Sigma(+)-1 4Sigma- potential energy surface intersections were calculated at the CASPT2 level, and the minima along the seams were located. The calculations indicate that within the experimental energy range (15.07-16.0 eV) the 2 2Pi(A 2Pi) state can be predissociated by 1 4Sigma- forming the S+(4Su) ion and can undergo internal conversion to 1 2Pi followed by the direct dissociation of 1 2Pi forming S+(2Du) and that within the experimental energy range (16.04-16.54 eV) the 1 2Sigma+(B 2Sigma+) state can be predissociated by 1 4Sigma- forming the S+(4Su) ion and can undergo internal conversion to 2 2Pi followed by the predissociation of 2 2Pi by 1 2Sigma- and 1 2Delta forming the S+(2Du) ion. These indications are in line with the experimental fact that both the 4Su and 2Du states of the S+ ion can be formed from the 2 2Pi and 1 2Sigma+ states of the OCS+ ion.     

A theoretical study of the fine and hyperfine interactions in the NCO and CNO radicals

The geometries, the harmonic vibrational frequencies, and the Renner-Teller parameter have been reported for the NCO(+)(X (3)Sigma(-)), NCO(X (2)Pi,A (2)Sigma(+),B (2)Pi,2 (2)Sigma(+)), NCO(-)(X (1)Sigma(+)), CNO(+)(X), CNO(X (2)Pi,A (2)Sigma(+),B (2)Pi,2 (2)Sigma(+)), and CNO(-)(X (1)Sigma(+)) systems at the full valence-complete active space self-consistent-field (fv-CASSCF) level of theory. The (2)Pi electronic states of the NCO and CNO radicals have two distinct real vibrational frequencies for the bending modes and these states are subject to the type A Renner-Teller effect. The total energy of CNO(+) without zero point energy correction of the linear geometry is approximately 31 cm(-1) higher than the bent geometry at the fv-CASSCF level and the inversion barrier vanishes after the zero point energy correction; therefore, the ground state of the CNO(+) may possess a quasilinear geometry. The spin-orbit coupling constants estimated using atomic mean field Hamiltonian at the fv-CASSCF level of theory are in better agreement with the experimental values. The excitation energies, the electron affinity, and the ionization potential have been computed at the complete active space second order perturbation theory (CASPT2) and the multireference singles and doubles configuration (MRSD-CI) levels of theory. The computed values of the electric hyperfine coupling constants for the (14)N atom in the ground state of the NCO radical agree well with the experimental data. The magnetic hyperfine coupling constants (HFCC's) have been estimated employing the configuration selected MRSD-CI and the multireference singles configuration interaction (MRS-CI) methods using iterative natural orbitals (ino) as one particle basis. Sufficiently accurate value of the isotropic contribution to the HFCC's can be obtained using an MRS-CI-ino procedure.     

Application of mean-field and surface-hopping approaches for interrogation of the Xe3+ molecular ion photoexcitation dynamics

The dissociation dynamics of the excited Xe(3) (+) molecular ion through the Pi(12)(u) and Pi(12)(g) conical intersection was interrogated by computational simulation in which no adjustable parameters were used. The electronic ground and excited state potential energy surfaces were generated by the diatomics-in-molecules method, and the Ehrenfest mean-field and Tully surface-hopping approaches treated the nonadiabatic interactions. Reproduction of the experimental spectrum of the symmetric photofragmentation as a function of excitation energy was obtained within the region of interest (2.5-3.75 eV), with the exception of a 0.25 eV width on the red side of the spectral apex. Good agreement was obtained with the experimental dissociated photofragment kinetic energy spectra. It was determined that the greatest contribution to the nonadiabatic coupling between the two states originated from the bending vibrational mode of the molecule in the Sigma(12)(u), ground electronic state before excitation.     

Parallel and coupled perpendicular transitions of RbCs 640 nm system: mass-resolved resonance enhanced two-photon ionization in a cold molecular beam

We have investigated the RbCs 640 nm system by mass-resolved resonance enhanced two-photon ionization in a cold molecular beam. Very complex vibronic structures were observed between 15420 and 15990 cm (-1). The parallel transitions of 2 (3)Pi 0 v' = 4-20 <-- X (1)Sigma (+) v' = 0 were identified by rotationally resolved spectra. Molecular constants and a Rydberg-Klein-Rees potential energy curve of the 2 (3)Pi 0 state were determined. The regular vibrational spacing of the parallel transition indicated that the 2 (3)Pi 0 state is not significantly perturbed by nearby excited electronic states. The complexity of the observed vibronic structures has been attributed to the coupled perpendicular transitions of 2 (1)Pi, 2 (3)Pi 1, and 3 (3)Sigma 1 (+) <-- X (1)Sigma (+) v' = 0. For the perpendicular bands observed in the lower-energy spectral region between 15420 and 15630 cm (-1) where the onsets of the 2 (3)Pi 1 and 3 (3)Sigma 1 (+) <-- X (1)Sigma (+) transitions are located, the upper electronic states and the vibrational quantum numbers were assigned. Perturbations of 2 (3)Pi 1-3 (3)Sigma 1 (+) and 2 (1)Pi-3 (3)Sigma 1 (+) have been identified by the observed level shifts.     

Photoelectron imaging of hydrated carbon dioxide cluster anions

The effects of homogeneous and heterogeneous solvation on the electronic structure and photodetachment dynamics of hydrated carbon dioxide cluster anions are investigated using negative-ion photoelectron imaging spectroscopy. The experiments are conducted on mass-selected [(CO(2))(n)()(H(2)O)(m)()](-) cluster anions with n and m ranging up to 12 and 6, respectively, for selected clusters. Homogeneous solvation in (CO(2))(n)()(-) has minimal effect on the photoelectron angular distributions, despite dimer-to-monomer anion core switching. Heterogeneous hydration, on the other hand, is found to have the marked effect of decreasing the photodetachment anisotropy. For example, in the [CO(2)(H(2)O)(m)()](-) cluster anion series, the photoelectron anisotropy parameter falls to essentially zero with as few as 5-6 water molecules. The analysis of the data, supported by theoretical modeling, reveals that in the ground electronic state of the hydrated clusters the excess electron is localized on CO(2), corresponding to a (CO(2))(n)()(-).(H(2)O)(m)() configuration for all cluster anions studied. The diminishing anisotropy in the photoelectron images of hydrated cluster anions is proposed to be attributable to photoinduced charge transfer to solvent, creating transient (CO(2))(n)().(H(2)O)(m)()(-) states that subsequently decay via autodetachment.     

Electronic states and spectroscopic properties of SiTe and SiTe+

Ab initio based configuration interaction calculations have been carried out to study the low-lying electronic states and spectroscopic properties of the heaviest nonradioactive silicon chalcogenide molecule and its monopositive ion. Spectroscopic constants and potential energy curves of states of both SiTe and SiTe+ within 5 eV are reported. The calculated dissociation energies of SiTe and SiTe+ are 4.41 and 3.52 eV, respectively. Effects of the spin-orbit coupling on the electronic spectrum of both the species are studied in detail. The spin-orbit splitting between the two components of the ground state of SiTe+ is estimated to be 1880 cm(-1). Transitions such as 0+ (II)-X1Sigma(+)0+, 0+ (III)-X1Sigma(+)0+, E1Sigma(+)0+ -X1Sigma(+)0+, and A1Pi1-X1Sigma(+)0+ are predicted to be strong in SiTe. The radiative lifetime of the A1Pi state is less than a microsecond. The X(2)2Pi(1/2)-X(1)2Pi(3/2) transition in SiTe+ is allowed due to spin-orbit mixing. However, it is weak in intensity with a partial lifetime for the X2 state of about 108 ms. The electric dipole moments of both SiTe and SiTe+ in their low-lying states are calculated. The vertical ionization energies for the ionization of the ground-state SiTe to different ionic states are also reported.     

The low-lying electronic excited states of NiCO

Highly correlated coupled cluster methods with single and double excitations (CSSD) and CCSD with perturbative triple excitations were used to predict molecular structures and harmonic vibrational frequencies for the electronic ground state X 1Sigma+, and for the 3Delta, 3Sigma+, 3Phi, 1 3Pi, 2 3Pi, 1Sigma+, 1Delta, and 1Pi excited states of NiCO. The X 1Sigma+ ground state's geometry is for the first time compared with the recently determined experimental structure. The adiabatic excitation energies, vertical excitation energies, and dissociation energies of these excited states are predicted. The importance of pi and sigma bonding for the Ni-C bond is discussed based on the structures of excited states.