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.     

Ground state potential energy curve and dissociation energy of MgH

New high-resolution visible emission spectra of the MgH molecule have been recorded with high signal-to-noise ratios using a Fourier transform spectrometer. Many bands of the A 2Pi-->X 2Sigma+ and B' 2Sigma+-->X 2Sigma+ electronic transitions of 24MgH were analyzed; the new data span the v' = 0-3 levels of the A 2Pi and B'2Sigma+ excited states and the v'=0-11 levels of the X 2Sigma+ ground electronic state. The vibration-rotation energy levels of the perturbed A 2Pi and B' 2Sigma+ states were fitted as individual term values, while those of the X 2Sigma+ ground state were fitted using the direct-potential-fit approach. A new analytic potential energy function that imposes the theoretically correct attractive potential at long-range, and a radial Hamiltonian that includes the spin-rotation interaction were employed, and a significantly improved value for the ground state dissociation energy of MgH was obtained. The v'=11 level of the X 2Sigma+ ground electronic state was found to be the highest bound vibrational level of 24MgH, lying only about 13 cm(-1) below the dissociation asymptote. The equilibrium dissociation energy for the X 2Sigma+ ground state of 24MgH has been determined to be De=11104.7+/-0.5 cm(-1) (1.37681+/-0.00006 eV), whereas the zero-point energy (v'=0) is 739.11+/-0.01 cm(-1). The zero-point dissociation energy is therefore D0=10365.6+/-0.5 cm(-1) (1.28517+/-0.00006 eV). The uncertainty in the new experimental dissociation energy of MgH is more than 2 orders of magnitude smaller than that for the best value available in the literature. MgH is now the only hydride molecule other than H2 itself for which all bound vibrational levels of the ground electronic state are observed experimentally and for which the dissociation energy is determined with subwavenumber accuracy.     

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.     

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.     

The ionization energy of Be2, and spectroscopic characterization of the (1)3Sigmau+, (2)3Pig, and (3)3Pig states

Low lying electronic states of the beryllium dimer were investigated by laser induced fluorescence (LIF) and resonance enhanced multiphoton ionization (REMPI) techniques. Be(2) was formed by pulsed laser ablation of Be metal in the presence of helium carrier gas, followed by a free jet expansion into vacuum. Several previously unobserved states of the dimer were characterized. These included transitions of the triplet manifold (2)(3)Pi(g) <-- (1)(3)Sigma(u)+ and (3)(3)Pi(g) <-- (1)(3)Sigma(u)+, for which rotationally resolved bands were obtained. In addition, transitions to the v' = 10-18 vibrational levels of the A (1)Pi(u) state were recorded. Photoionization efficiency (PIE) measurements were used to determine an accurate ionization energy (IE) for Be(2) of 7.418(5) eV and the term energy for (1)(3)Sigma(u)+. Above the ionization threshold the PIE spectrum was found to be highly structured, consisting of overlapping Rydberg series that converged on excited vibrational levels of Be(2)+. Analysis of these series yielded a vibration frequency for the X(2)Sigma(u)+ state of 498(20) cm(-1). The bond dissociation energy for Be(2)+, deduced from the IE measurement, was 16 072(40) cm(-1). Multi-reference configuration interaction (MRCI) calculations were carried out for Be(2) and Be(2)+, yielding results that were in excellent agreement with the experimental observations.     

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.     

Electronic quenching of OH A 2Sigma+ radicals in single collision events with H2 and D2: a comprehensive quantum state distribution of the OH X 2Pi products

A pump-probe laser-induced fluorescence technique has been used to examine the nascent OH X (2)Pi product state distribution arising from non-reactive quenching of electronically excited OH A (2)Sigma(+) by molecular hydrogen and deuterium under single-collision conditions. The OH X (2)Pi products were detected in v'=0, 1 and 2; the distribution peaks in v'=0 and decreases monotonically with increasing vibrational excitation. In all vibrational levels probed, the OH X (2)Pi products are found to be highly rotationally excited, the distribution peaking at N'=15 when H(2) was used as the collision partner and N'=17 for D(2). A marked propensity for production of Pi(A') Lambda-doublet levels was observed, while both OH X (2)Pi spin-orbit manifolds were equally populated. These observations are interpreted as dynamical signatures of the nonadiabatic passage of the OH + H(2)/D(2) system through the seams of conical intersection that couple the excited state (2 (2)A') and ground state (1 (2)A') surfaces.     

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.     

Two-color visible/vacuum ultraviolet photoelectron imaging dynamics of Br2

An experimental two-color photoionization dynamics study of laser-excited Br2 molecules is presented, combining pulsed visible laser excitation and tunable vacuum ultraviolet (VUV) synchrotron radiation with photoelectron imaging. The X 1Sigmag + -B 3Pi0+u transition in Br2 is excited at 527 nm corresponding predominantly to excitation of the v' = 28 vibrational level in the B 3Pi0+u state. Tunable VUV undulator radiation in the energy range of 8.40-10.15 eV is subsequently used to ionize the excited molecules to the X 2Pi32,12 state of the ion, and the ionic ground state is probed by photoelectron imaging. Similar experiments are performed using single-photon synchrotron ionization in the photon energy range of 10.75-12.50 eV without any laser excitation. Photoelectron kinetic energy distributions are extracted from the photoelectron images. In the case of two-color photoionization using resonant excitation of the intermediate B 3Pi0+u state, a broad distribution of photoelectron kinetic energies is observed, and in some cases even a bimodal distribution, which depends on the VUV photon energy. In contrast, for single-photon ionization, a single nearly Gaussian-shaped distribution is observed, which shifts to higher energy with photon energy. Simulated spectra based on Franck-Condon factors for the transitions Br2(X 1Sigmag+, v" = 0)-Br2 +(X 2Pi12,32, v+) and Br2(B 3Pi0+u, v' = 28)-Br2 +(X 2Pi12,32, v+) are generated. Comparison of these calculated spectra with the measured images suggests that the differences in the kinetic energy distributions for the two ionization processes reflect the different extensions of the vibrational wave functions in the v" = 0 electronic ground state (X 1Sigmag+) versus the electronically and vibrationally excited state (B 3Pi0+u, v' = 28).     

Near-infrared laser spectroscopy of NiI

Laser-induced fluorescence spectrum of NiI in the near infrared region of 714-770 nm has been recorded. Seven bands belonging to three electronic transition systems were observed and analyzed: the (0,0), (1,0), and (2,0) bands of [13.3] (2)Sigma(+)-A (2)Pi(3/2) system; the (1,1) and (0,1) bands of [13.9] (2)Pi(3/2)-X (2)Delta(5/2) system; and the (0,0) and (1,0) bands of [13.9] (2)Pi(3/2)-A (2)Pi(3/2) system. Spectra of isotopic molecules confirmed the vibrational quantum number assignment of the observed bands. Least-squares fit of rotationally resolved transition lines yielded accurate molecular constants for the v=0-2 levels of the [13.3] (2)Sigma(+) state, the v=0 level of the A (2)Pi(3/2), and the v=1 level of the X (2)Delta(5/2) state. The vibrational separation, DeltaG(1/2), of the ground state was measured to be 276.674 cm(-1). With the observation of the [13.9] (2)Pi(3/2)-A (2)Pi(3/2) and [13.9] (2)Pi(3/2)-X (2)Delta(5/2) transitions, we accurately determined the energy separation between the A (2)Pi(3/2) and the X (2)Delta(5/2) to be 163.847 cm(-1). This confirms that the order of the A (2)Pi(3/2) and X (2)Delta(5/2) states in NiI is reversed when compared with other nickel monohalides.     

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.     

Experimental determination of energy disposal in the dissociative electron recombinations of CS2(+) and HCS2(+)

Vibronic optical emissions from CS(A1pi --> X1sigma+) and CS(a3pi --> X1sigma+) transitions have been identified from dissociative recombination (DR) of CS2(+) and HCS2(+) plasmas. All of the spectra were taken in flowing afterglow plasmas using an optical monochromator in the UV-visible wavelength region of 180-800 nm. For the CS(A --> X) and CS(a --> X) emissions, the relative vibrational distributions have been calculated for v' < 5 and v' < 3 in both types of plasmas for the CS(A) and CS(a) states, respectively. Both recombining plasmas show a population inversion from the v' = 0 to v' = 1 level of the CS(A) state, similar to other observations of the CS(A) state populations, which were generated using two other energetic processes. The possibility of spectroscopic cascading is addressed, such that transitions from upper level electronic states into the CS(A) and CS(a) states would affect the relative vibrational distribution, and there is no spectroscopic evidence supporting the cascading effect. Additionally, excited-state transitions from neutral sulfur (S(5S(2)0 --> 3P(2)) and S(5S(2)0 --> 3P(1))) and the products of ion-molecule reactions (CS(B1sigma+ --> A1pi), CS(+)(B2sigma+ --> A2pi(i)), and CS2(+) (A2pi(u) --> X2pi(g))) have been observed and are discussed.     

(2+1) resonance-enhanced ionization spectroscopy of a state-selected beam of OH radicals

A state-selected beam of hydroxyl radicals is generated using a pulsed discharge source and hexapole field. The OH radicals are characterized by resonance-enhanced multiphoton ionization (REMPI) spectroscopy via the nested D 2Sigma- and 3 2Sigma- Rydberg states. Simplified spectra are observed from the selected |MJ|=3/2 component of the upper Lambda-doublet level of the lowest rotational state (J=32) in ground (v"=0) and excited (v"=1-3) vibrational levels of the OH X 2Pi3/2 state. Two-photon transitions are observed to the D 2Sigma-(v'=0-3) and 3 2Sigma-(v'=0,1) vibronic levels, extending previous studies to higher vibrational levels of the Rydberg states. Spectroscopic constants are derived for the Rydberg states and compared with prior experimental studies. Complementary first-principle theoretical studies of the properties of the D 2Sigma- and 3 2Sigma- Rydberg states [see M. P. J. van der Loo and G. C. Groenenboom, J. Chem. Phys. 123, 074310 (2005), following paper] are used to interpret the experimental findings and examine the utility of the (2+1) REMPI scheme for sensitive detection of OH radicals.     

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.     

Electronic angular momentum polarizations of photofragments: a case study of ICN photodissociation from a perpendicular transition

A quantum treatment on ICN photodissociation from an initial perpendicular transition (Omega'=+/-1<--Omega"=0) to the asymptote CN(|Sigma+,J'M'N'1/2>)+I(2P3/2) is presented. Density matrices of both photofragments are derived and explicit expressions of the state multipoles in terms of the angular momentum coupling coefficients and the rotation-bending factors have been obtained. To perceive the physical origin of electronic angular momentum polarizations of the iodine photofragments, a correlation scheme which considers the magnetic dipolar and the electrostatic dipole-quadrupole interactions between I and CN cofragments is proposed. For ICN precursors in the vibrational ground state or in the equally populated l-type split levels, the alignment parameters of the iodine photofragments in the molecular frame can be calculated according to this long-range interaction model. For the perpendicular transition |1Pi1><--|1Sigma0+>, its alignment parameters of I(2P3/2) from the incoherent and coherent transitions to the |Omega'=1> and |Omega'=-1> components are rho(0)2(1Pi1)=0.756 and rho2(2)(1Pi1)=-0.656, respectively. For the perpendicular transition to |3Pi1>, rho(0)2(3Pi1)=-0.878 and rho2(2)(3Pi1)=0.328 are from the incoherent transition, whereas rho(0)2(3Pi1)=0.122 and rho2(2)(3Pi1)=0.328 are from the coherent transition. To analyze the photoion images of iodine photofragments, angular distributions of I+ from the 2+1 resonance-enhanced multiphoton ionization detection scheme are derived.     

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).     

High-resolution IR cavity ring-down spectroscopy of jet-cooled free radicals and other species

Initial spectral results are reported from a newly constructed cavity ringdown spectrometer. The apparatus incorporates a slit-jet expansion, with or without a discharge, to produce cold sample molecules. High spectral resolution in both the near- and mid-IR is obtained by using stimulated Raman scattering of the pulsed amplified output of a cw Ti:Sa ring laser. Molecular spectra presented include the electronic near-IR transitions a (1)Delta(g)(-)<-- X (3)Sigma(g)(-) of O(2) and B (3)Pi(g)<-- A (3)Sigma(u)(+) of metastable N(2) and vibrational overtones of H(2)O (polyad 2) and the OH radical. Fundamental vibrational transitions of CH(3) (nu(3)) in the mid-IR are also observed. This apparatus has demonstrated the potential for obtaining high-resolution spectra of both reactive and non-reactive species throughout the entire IR region.     

Experimental study of the NaK 3 3Pi double minimum state

We have used the Doppler-free, perturbation-facilitated optical-optical double-resonance technique to investigate the vibrational, rotational, and hyperfine structure of the 3 (3)Pi double minimum state of NaK. Since this electronic state arises from an avoided crossing with the nearby 4 (3)Pi state, we observe striking patterns in the data that provide a sensitive probe of the electronic wave function in the various regions of the double well potential. A single-mode cw dye laser excites 2(A) (1)Sigma(+)(v(A),J) approximately 1(b) (3)Pi(Omega=0)(v(b),J) mixed singlet-triplet "window" levels from thermally populated rovibrational ground state levels, 1(X) (1)Sigma(+)(v(X),J+/-1). Further excitation by a single-mode cw Ti:sapphire laser selects various 3 (3)Pi(0)(v(Pi),J(Pi)) rovibrational levels, which are detected by observing direct 3 (3)Pi(0)-->1(a) (3)Sigma(+) fluorescence in the green spectral region. Using the inverse perturbation approximation method, we have determined a 3 (3)Pi(0) potential curve that reproduces the measured energies to approximately 0.24 cm(-1). In addition, the hyperfine and spin-orbit constants, b(F) and A(v), have been determined for each region of the potential curve.     

Observation and calculation of the Cs2 2 3Delta(1g) and b 3Pi(0u) states

The Cs(2) 2 (3)Delta(1g) and b (3)Pi(0u) states have been observed by infrared-infrared double resonance spectroscopy for the first time. 221 2 (3)Delta(1g)<--A (1)Sigma(u) (+)<--X (1)Sigma(g) (+) double resonance lines have been assigned to transitions into the 2 (3)Delta(1g) v=6-13 vibrational levels. Resolved fluorescence into the b (3)Pi(0u) v(')=0-48 levels has been recorded. Molecular constants and potential energy curves are determined by the global fit of the entire set of the experimental data. Theoretical potential energy curves of the 2 (3)Delta(g) and b (3)Pi(u) states have been determined in the framework of the pseudopotential method and are compared with the experimental results.     

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.