Experimental determination of a spin-orbit interval in the C" 5Pi(ui) state of 14N2

We have developed an experimental setup using the combination of laser optogalvanic detection and a supersonic expansion of excited N2 to record the high resolution spectrum of the (3-1) and (4-2) Herman infrared bands (C" 5Pi(ui)-A' 5Sigma(g)+). We report the first experimental determination of a spin-orbit interval (about 24 cm(-1)) in the C" 5Pi(ui) state of N2 for both the (3-1) and (4-2) vibrational bands as well as the first observation of the v' = 4 vibrational level.     

The spin-orbit and rotational constants for the N2 C" 5Pi(ui) (v = 3) state

The spin-orbit (A = -16.4 cm(-1)) and rotational (B = 1.017 cm(-1)) constants for the N2 C" 5Pi(ui)(v = 3) level are determined by a fit to rotational lines in the C" 5Pi(u)-A' 5Sigma(g)+(3-1) band that terminate in J'Omega' = 3(3), 4(3), 3(2), and 4(2) levels of the C" state. The C"-state spin-orbit constant is consistent with semi-empirical estimates, based on spin-orbit constants observed in several other electronic states of N2 and the atomic spin-orbit coupling constant, zeta(N 2p). The C"-A' bands exhibit the unusual feature of oppositely degraded sub-band heads, Omega' = 3 (red) and Omega' = 1, 0, and -1 (blue). The unusually wide range of B(Omega)eff values, from 0.85 cm(-1) (Omega = 3) to 1.28 cm(-1) (Omega = -1) for C" 5Pi(v = 3) should be diagnostically useful for Omega'-assignments. The C" 5Pi(v = 3) level lies 14257.17 and 90599 cm(-1) above A' 5Sigma(g)+(v = 1) and X 1Sigma(g)+(v = 0), respectively, and Re(C" 5Pi) = 1.50 A.     

Renner-Teller effect in C2H2+(X2Pi u) studied by rotationally resolved zero kinetic energy photoelectron spectroscopy

The Renner-Teller effect in C(2)H(2)(+)(X(2)Pi(u)) has been studied by using zero kinetic energy (ZEKE) photoelectron spectroscopy and coherent extreme ultraviolet (XUV) radiation. The rotationally resolved vibronic spectra have been recorded for energies up to 2000 cm(-1) above the ground vibrational state. The C triple bond C symmetric stretching (upsilon(2)), the CCH trans bending (upsilon(4)), and the CCH cis bending (upsilon(5)) vibrational excitations have been observed. The assigned vibronic bands are 4(1)(1)(kappa(2)Sigma(u)(+))(hot band), 4(1)(0)(mu/kappa(2)Sigma (u)(-/+)), 5(1)(0)(mu/kappa(2)Sigma (g)(+/-)), and 4(2)(0)(mu(2)Pi(u)), 4(2)(0)(kappa(2)Pi(u)), 4(1)(0)5(1)(0) (mu(2)Pi(g)), 0(0)(0)(X(2)Pi(u)), and 2(1)(0)(X(2)Pi(u)). The Renner-Teller parameters, the harmonic frequencies, the spin-orbit coupling constants, and the rotational constants for the corresponding vibronic bands have been determined by fitting the spectra with energy eigenvalues from the Hamiltonian that considers simultaneously Renner-Teller coupling, vibrational energies, rotational energies, and spin-orbit coupling interaction.     

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 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).     

Spin-forbidden transitions in the vicinity of the 2 (1)pi(u) <-- X (1)sigma(g)+ band system of Rb2

We have investigated the Rb2 475 nm system by resonance enhanced two-photon ionization spectroscopy in a pulsed molecular beam. Strong extra bands accompanying the 2 (1)Pi(u) v' = 5 - 8 <-- X (1)Sigma(g)(+) v' = 0 bands were newly observed. Rotational analysis of the main and extra bands reveals that the 2 (1)Pi(u) v' = 5 - 8 levels are significantly perturbed, mainly by the 3 (3)Sigma(u)(+)(1 u) state and also by the 2 (3)Pi(u)(1 u) state. For the major perturber, 3 (3)Sigma(u)(+)(1 u), the intensity borrowing has been found to be facilitated by the 2 (1)Pi(u)-3 (3)Sigma(u)(+)(1 u) potential energy curve crossing near 21,100 cm(-1). For the vibronic-band intensities of the 2 (3)Pi(u)(1 u) v' <-- X (1)Sigma(g)(+) v' = 0 transitions observed in this spectral region, intensity borrowing was most effective when the 2 (3)Pi(u)(1 u) levels were close to the 3 (3)Sigma(u)(+)(1 u) levels. A deperturbation fit for the perturbing bands has provided the 2 (1)Pi(u)-3 (3)Sigma(u)(+)(1 u) coupling constants.     

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.     

Spin-forbidden c 3Sigma1+<--X 1Sigma+ band system of YF

Optical spectra of jet-cooled diatomic YF have been recorded using resonant two-photon ionization spectroscopy. A vibrational progression corresponding to the c 3Sigma1+<--X 1Sigma+ system has been identified. The vibrational frequency omegae' and anharmonicity omegae'xe' of the c 3Sigma+ state are 546.70 and 2.45 cm-1, respectively. The 0-0, 1-0, and 2-0 bands of the c 3Sigma1+<--X 1Sigma+ system were rotationally resolved and analyzed, allowing the v'=0, 1, and 2 levels of the c 3Sigma1+ substate to be characterized. From these studies, Be'=0.269 81(3) cm-1, alphae'=0.001 72(3) cm-1, and re'=1.9979(1) A were obtained (1sigma error limits). For these levels the spin-spin coupling constant lambdav is identical within experimental error, as lambda=-22.5 cm-1. The spin-forbidden c 3Sigma1+<--X 1Sigma+ transition is made allowed by spin-orbit interaction between the c 3Sigma1+ and the B 1Pi states. Excited state lifetimes of the c 3Sigma1+ and the B 1Pi states have been measured as 7.11(41) and 0.133(15) micros, respectively. A spin-orbit analysis shows that the c 3Sigma1+ state is contaminated with 2% B 1Pi character, which is approximately sufficient to explain the 7 micros lifetime of the c 3Sigma1+ state.     

Rotational effects in the band oscillator strengths and predissociation linewidths for the lowest 1Pi u-X 1Sigmag+ transitions of N2

A coupled-channel Schrodinger equation (CSE) model of N2 photodissociation, which includes the effects of all interactions between the b, c, and o 1Pi u and the C and C' 3Pi u states, is employed to study the effects of rotation on the lowest-upsilon 1Pi u-X 1Sigmag+(upsilon,0) band oscillator strengths and 1Pi u predissociation linewidths. Significant rotational dependences are found which are in excellent agreement with recent experimental results, where comparisons are possible. New extreme-ultraviolet (EUV) photoabsorption spectra of the key b 1Pi u<--X 1Sigmag +(3,0) transition of N2 are also presented and analyzed, revealing a b(upsilon=3) predissociation linewidth peaking near J=11. This behavior can be reproduced only if the triplet structure of the C state is included explicitly in the CSE-model calculations, with a spin-orbit constant A approximately 15 cm(-1) for the diffuse C(upsilon=9) level which accidentally predissociates b(upsilon=3). The complex rotational behavior of the b-X(3,0) and other bands may be an important component in the modeling of EUV transmission through nitrogen-rich planetary atmospheres.     

Electronic states of sodium dimer in ammonia clusters: theoretical study of photoelectron spectra for Na2-(NH3)n (n = 0-6)

The geometries, energetics, and vertical detachment energies of Na2-(NH3)n (n = 0-6) were examined by ab initio molecular orbital methods in connection with their photoelectron spectra. One of the Na atoms is selectively solvated in the most stable structures for each n. The solvated Na is spontaneously ionized and the formation of a solvated electron occurs with increasing n, giving rise to the Na-Na+(NH3)n(e-)-type state. The ground and two lowest-lying excited states derived from the 11Sigma g+, 13Sigma u+, and 13Pi u states of Na2, respectively, are of ion-pair character though the 13Sigma u+-type state has an intermediate nature slowly changing to the radical-pair state with increasing n. On the other hand, the higher states stemming from the 11Sigma u+, 13Sigma g+, and 11Pi u states of Na2 show a developing radical-pair nature as n increases. The size dependences of the photoelectron spectra such as the near parallel shifts of the first and second bands, as well as the rapid red shifts of the higher bands, are studied on the basis of the electronic change of the neutrals by solvation.     

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.     

Is the HCCS radical linear in the excited state?

The A (2)Pi-X (2)Pi 415 nm band system of the linear HCCS radical has been known since 1978, but the vibronic structure in this complex spectrum, which has both spin-orbit and Renner-Teller complications, has never been satisfactorily assigned, despite serious experimental and theoretical efforts. In a further attempt to understand the spectrum, we have studied the laser-induced fluorescence spectra of jet-cooled HCCS and DCCS, produced from thiophene precursors using the discharge jet technique. The 0(0) (0) bands of HCCS and DCCS have been rotationally analyzed, providing precise ground and excited state spin-orbit splittings. The energy levels of the v(')=0 (2)Pi(3/2) component of DCCS are found to be perturbed by a very low-lying (2)Sigma vibronic level, indicating that the HCC bending mode Renner-Teller effect is much larger than predicted by ab initio calculations with a linear excited state geometry. With this observation, the vibronic bands in the spectra of both isotopomers have been consistently assigned for the first time. Model calculations show that the large Renner-Teller effect and substantially different HCCS and DCCS excited state zero-point spin-orbit splittings can be explained with the assumption of a quasilinear excited state geometry.     

Photodissociation spectroscopy of stored CH+ and CD+ ions: analysis of the b 3Sigma(-)-a 3Pi system

We have measured the photodissociation spectrum of CH(+) and CD(+) molecular ions, stored as fast (MeV) ion beams in the heavy-ion storage ring TSR. Several b (3)Sigma(-)-a (3)Pi bands were observed as strong resonances because a large fraction of the ions in the metastable a (3)Pi(v=0) state were pumped to b (3)Sigma(-) levels and predissociated via the c (3)Sigma(+) state into C(+) and H(D) fragments. From a rotational analysis of the 2-0, 3-0, and 4-0 bands in CH(+) and the 3-0 and 4-0 bands in CD(+), we derive spectroscopic constants for these levels and also revise a previous analysis of the 0-0 and 1-0 bands in CH(+). Combining all data delivers new, significantly adjusted equilibrium constants for the b (3)Sigma(-) and a (3)Pi electronic states. Apart from the spectroscopic analysis, we estimate the predissociation rates of the upper b (3)Sigma(-) vibrational levels in CH(+) and compare them to a model. For the initial rovibrational distribution of the stored metastable CH(+) molecules, the data indicate a faster vibrational cooling than derived before, and rotational cooling at a rate similar to the X (1)Sigma(+) ground state. New aspects of the spin-forbidden a (3)Pi-X (1)Sigma(+) radiative decay are discussed. Finally, we predict b (3)Sigma(-)-a (3)Pi absorption and a (3)Pi-X (1)Sigma(+) emission lines through which CH(+) in the metastable a (3)Pi(v=0) state might be detectable in astrophysical environments.     

The 4051-Angstroms band of C3 (A 1Piu-X 1Sigmag +, 000-000): perturbed low-J lines and lifetime measurements

Rotational analyses have been carried out at high resolution for the 000-000 and 000-100 bands of the A (1)Pi(u)-X (1)Sigma(g) (+) transition of supersonic jet-cooled C(3). Two different spectra have been recorded for each band, using time gatings of 20-150 and 800-2300 ns. At the shorter time delay the spectra show only the lines observed by many previous workers. At the longer time delay many extra lines appear, some of which have been observed previously by [McCall et al.Chem. Phys. Lett. 374, 583 (2003)] in cavity ring-down spectra of jet-cooled C(3). Detailed analysis of these extra lines shows that at least two long-lived states perturb the A (1)Pi(u), 000 state. One of these appears to be a (3)Sigma(u) (-) vibronic state, which may possibly be a high vibrational level of the b (3)Pi(g) state, and the other appears to be a P = 1 state with a low rotational constant B. Our spectra also confirm the reassignment by McCall et al. of the R(0) line of the 000-000 band, which is consistent with the spectra recorded towards a number of stars that indicate the presence of C(3) in the interstellar medium. Fluorescence lifetimes have been measured for a number of upper-state rotational levels. The rotational levels of the A (1)Pi(u) state have lifetimes in the range of 230-190 ns, decreasing slightly with J; the levels of the perturbing states have much longer lifetimes, with some of them showing biexponential decays. An improved value has been obtained for the nu(1) vibrational frequency of the ground state, nu(1) = 1224.4933 +/- 0.0029 cm(-1).     

Quartet states of the acetylene cation: electronic structure calculations and spin-orbit coupling terms

Highly correlated ab initio methods have been used to generate one-dimensional cuts of the six-dimensional potential energy surfaces of the quartet and lowest doublet states for the HCCH(+) ion along the CH, CC, and cis and trans bending coordinates. Transition dipole moments and spin-orbit matrix elements are deduced. For the lowest 1 (4)Sigma(u) (+) state, the calculations predict a possible photon emission through the 1 (4)Pi(g)<--1 (4)Sigma(u) (+) transition competing with internal conversion and predissociation processes. The potential surfaces are used together with spin-orbit matrix elements to discuss the metastability and the predissociation processes forming the C(2)HC(2)H(+)+H(+)H products. Multistep spin-orbit induced predissociation pathways are suggested.     

C6- electronic relaxation dynamics probed via time-resolved photoelectron imaging

Anion time-resolved photoelectron imaging has been used to investigate the electronic relaxation dynamics of C(6) (-) following excitation of the C (2)Pi(g)<--X (2)Pi(u) and 2 (2)Pi(g)<--X (2)Pi(u) 0(0) (0) transitions at 607 and 498 nm, respectively. Analysis of evolving photodetachment energy distributions reveals differing relaxation pathways from these prepared states. Specifically, the C (2)Pi(g) 0(0) level relaxes on a time scale of 620+/-30 fs to vibrationally hot ( approximately 2.0 eV) anion ground state both directly and indirectly through vibrationally excited levels of the intermediate-lying A (2)Sigma(g) (+) state that decay with a time scale of 2300+/-200 fs. In contrast, the 2 (2)Pi(g) 0(0) level relaxes much more quickly (<100 fs) to vibrationally hot ( approximately 2.5 eV) anion ground state directly and with transient population accumulation in the A (2)Sigma(g) (+), B (2)Sigma(u) (+), and C (2)Pi(g) electronic levels, as determined by spectral and time-scale analyses. This work also presents the experimental observation of the optically inaccessible B (2)Sigma(u) (+) state, which is found to have an electronic term value of 1.41+/-0.05 eV.     

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).     

Laser induced fluorescence spectroscopy of the C3N radical

Electronic spectra of the C3N radical have been observed for the first time in the near ultraviolet wavelength region by laser induced fluorescence (LIF) spectroscopy. Seventeen vibronic bands of the B 2Pii-X 2Sigma+ electronic transition system of C3N were identified in LIF spectra of products in a discharge of HC3N. The origin of the B 2Pii state was determined to be 27,929.985(1) cm(-1) from rovibrational analyses. It was found that observations of two types of 2Sigma vibronic levels, which have 2Sigma+ and 2Sigma+/- symmetries originated from excitations of the nu4 trans-bending mode (omega4=369.1(20) cm(-1)) with a large Renner-Teller (RT) interaction (epsilon4=-0.1549(50)), and the nu5 cis-bending mode (omega5=163.24(84) cm(-1)) with a small Renner-Teller interaction (epsilon5=-0.0503(68)), respectively. Vibronic levels, with excitations of the C-C stretching (omega3=869.7 cm(-1)) mode, were also identified. The spin-orbit interaction constant was determined to be Aso=-36.7(50) cm(-1) from the RT analysis. In dispersed fluorescence spectra from B 2Pii, vibrational structures of the low-lying electronically excited A 2Pii state were clearly observed with a strong progression due to the nu3' mode, together with those of the X 2Sigma+ state with weak intensities. The origin of A 2Pii, T0=1844(3) cm(-1), and the vibrational frequencies, omega3'=883(3) cm(-1) and omega5'=121(3) cm(-1) for A 2Pii, and omega3"=1054(3) cm(-1), omega4"=405(3) cm(-1), and omega5"=131(3) cm(-1) for X 2Sigma+, were determined. Time profiles of fluorescence from B 2Pii have short (50-200 ns) and long (>1 micros) decay components with quantum beats, indicating that there is a competition between radiative decay and the nonradiative internal conversion to vibrationally highly excited A 2Pii and X 2Sigma+.     

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.