The 39K(2) 2(3)Sigma(g)+ state: observation and analysis

The (39)K(2) 2 (3)Sigma(g) (+) state has been observed by perturbation-facilitated infrared-infrared double resonance spectroscopy and two-photon excitation. Resolved fluorescence spectra into the a (3)Sigma(u) (+) state have been recorded. The observed vibrational levels have been assigned as the v=23-25, 27, 28, 31-33, 38-45, 47, and 53 levels by comparing the observed and calculated spectra of the 2 (3)Sigma(g) (+)-->a (3)Sigma(u) (+) transitions. Molecular constants have been obtained using a global fitting procedure with a comprehensive set of experimental data. Fine and hyperfine splittings have been resolved in the excitation spectra. Perturbations between the 2 (3)Sigma(g) (+) and 2 (3)Pi(g) states were observed. The hyperfine patterns of the 2 (3)Sigma(g) (+) levels are strongly affected by the perturbation. The perturbation-free and weakly perturbed levels follow the case b(betaS) coupling scheme, while the perturbed levels follow case b(beta J) coupling. A Fermi contact constant, b(F)=65+/-10 MHz, has been obtained. Intensity anomalies of rotational lines appeared both in the 2 (3)Sigma(g) (+) approximately 2 (3)Pi(g)<--b (3)Pi(u) excitation spectra and in the 2 (3)Sigma(g) (+) approximately 2 (3)Pi(g)-->a (3)Sigma(u) (+) resolved fluorescence spectra. These intensity anomalies can be explained in terms of a quantum-mechanical interference effect.     

Observation of the 3(3)Sigma(+)-X1Sigma+ transition of KRb by resonance enhanced two-photon ionization in a pulsed molecular beam: Hyperfine structures of 39K85Rb and 39K87Rb isotopomers

The 3(3)Sigma(+)-X1Sigma+ transition of KRb is observed by resonance enhanced two-photon ionization in a pulsed molecular beam. Hyperfine splittings of 39K85Rb and 39K87Rb isotopomers are observed. From the magnitude of hyperfine splittings, we found that the main hyperfine structure was dominated by the Fermi contact interaction between the Rb nuclear spin and the unpaired electron spin. The Fermi contact interaction constants were determined to be 291 MHz for 39K85Rb and 665 MHz for 39K87Rb. In the KRb 3(3)Sigma+ state the electron spin couples more strongly with the Rb nuclear spin than with other angular momenta, and the energy level structure is well described by the hyperfine angular momentum coupling scheme of the b(betaS) case. The molecular constants and the Rydberg-Klein-Rees potential energy curve of the 3(3)Sigma+ state were determined.     

The Na2 2 3pi(g) state: new observations and hyperfine structure

Many more Na2 2 3pi(g) v = 0-43, omega = 0, 1, 2 levels have been observed by sub-Doppler continuous wave perturbation facilitated optical-optical double resonance fluorescence excitation spectroscopy and the hyperfine structure of the omega = 0 and 2 levels has been resolved. New molecular constants for the less perturbed v = 0-43 levels have been obtained with these new and the previously reported data. The hyperfine coupling scheme of the observed 2 3pi(g) levels is close to Hund's case a(beta) with a Fermi contact constant b(F) = 160+/-5 MHz, which is smaller than the Fermi contact constants of other Na2 triplet Rydberg states, b(F) = 200-245 MHz.     

The Zeeman tuning of the A 6Sigma+-X 6Sigma+ transition of chromium monohydride

The magnetic tuning of the low-rotational levels of the A (6)Sigma(+) (v = 1 and 0) states of chromium monohydride, (52)CrH, have been experimentally investigated using optical spectroscopy of the (0, 0) and (1, 0) bands of the A (6)Sigma(+)-X (6)Sigma(+) transition. The tuning of the numerous low-rotational lines in the A (6)Sigma(+)-X (6)Sigma(+) (0, 0) band can be accurately modeled using a single set of g-factors (g(S) and g(l)) which are close to the expected values. In contrast, the g-factors for the A (6)Sigma(+) (v = 1) state required to model the magnetic tuning of low-rotational lines in the A (6)Sigma(+)-X (6)Sigma(+) (1, 0) band are strongly dependent upon rotational and fine structure component and the determined effective values for g(S) deviate significantly from 2.002. Interpretation of the quantum level variation of g(S) is presented. The magnetic hyperfine structure of the (0, 0) and (1, 0) bands of the A (6)Sigma(+)-X (6)Sigma(+) transition is analyzed to produce proton Fermi contact, b(F) and dipolar, c, magnetic hyperfine parameters of 19(1) MHz and 34(5) MHz for the A (6)Sigma(+) (v = 0) state and 21(2) MHz and 30(7) MHz for the A (6)Sigma(+) (v = 1) state.     

Molecules in high spin states III: the millimeter/submillimeter-wave spectrum of the MnCl radical (X (7)Sigma(+))

The pure rotational spectrum of the MnCl radical (X (7)Sigma(+)) has been recorded in the range 141-535 GHz using millimeter-submillimeter direct absorption spectroscopy. This work is the first time the molecule has been studied with rotational resolution in its ground electronic state. MnCl was synthesized by the reaction of manganese vapor, produced in a Broida-type oven, with Cl(2). Transitions of both chlorine isotopomers were measured, as well as lines originating in several vibrationally excited states. The presence of several spin components and manganese hyperfine interactions resulted in quite complex spectra, consisting of multiple blended features. Because 42 rotational transitions were measured for Mn(35)Cl over a wide range of frequencies with high signal-to-noise, a very accurate set of rotational, fine structure, and hyperfine constants could be determined with the aid of spectral simulations. Spectroscopic constants were also determined for Mn(37)Cl and several vibrationally excited states. The values of the spin-rotation and spin-spin parameters were found to be relatively small (gamma=11.2658 MHz and lambda=1113.10 MHz for Mn(35)Cl); in the case of lambda, excited electronic states contributing to the second-order spin-orbit interaction may be canceling each other. The Fermi contact hyperfine term was found to be large in manganese chloride with b(F)(Mn(35)Cl)=397.71 MHz, a result of the manganese 4s character mixing into the 12sigma orbital. This orbital is spsigma hybridized, and contains some Mn 4psigma character, as well. Hence, it also contributes to the dipolar constant c, which is small and positive for this radical (c=32.35 MHz for Mn(35)Cl). The hyperfine parameters in MnCl are similar to those of MnH and MnF, suggesting that the bonding in these three molecules is comparable.     

The NaK 1(b) 3Pi(Omega=0) state hyperfine structure and the 1(b) 3Pi(Omega=0) approximately 2(A) 1Sigma+ spin-orbit interaction

We have measured the hyperfine structure of mutually perturbing rovibrational levels of the 1(b) 3Pi0 and 2(A) 1Sigma+ states of the NaK molecule, using the perturbation-facilitated optical-optical double resonance method with copropagating lasers. The unperturbed 1(b) 3Pi0 levels are split into four hyperfine components by the Fermi contact interaction bFIS. Mixing between the 1(b) 3Pi0 and 2(A) 1Sigma+ levels imparts hyperfine structure to the nominally singlet component of the perturbed levels and reduces the hyperfine splitting of the nominally triplet component. Theoretical analysis relates these observations to the hyperfine splitting that each 1(b) 3Pi0 level would have if it were not perturbed by a 2(A) 1Sigma+ level. Using this analysis, we demonstrate that significant hyperfine splitting arises because the 1(b) 3Pi0 state cannot be described as pure Hund's case (a). We determine bF for the 1(b) 3Pi0 levels and also a more accurate value for the magnitude of the singlet-triplet spin-orbit coupling HSO=[1(b) 3Pi0(vb,J)(H(SO))2(A) 1Sigma+(vA,J). Using the known spectroscopic constants of the 1(b) 3Pi state, we obtain bF=0.009 89+/-0.000 27 cm(-1). The values of (H(SO)) are found to be between 2 and 3 cm(-1), depending on vb, vA, and J. Dividing (H(SO)) by calculated vibrational overlap integrals, and taking account of the 1(b) 3Pi(Omega) rotational mixing, we can determine the magnitude of the electronic part H(el) of H(SO). Our results yield (H(el))=(16.33+/-0.15) cm(-1), consistent with our previous determinations using different techniques.     

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).     

Full configuration interaction potential energy curves for the X (1)Sigma(g) (+), B (1)Delta(g), and B(') (1)Sigma(g) (+) states of C(2): a challenge for approximate methods

The C(2) molecule exhibits unusual bonding and several low-lying excited electronic states, making the prediction of its potential energy curves a challenging test for quantum chemical methods. We report full configuration interaction results for the X (1)Sigma(g) (+), B (1)Delta(g), and B(') (1)Sigma(g) (+) states of C(2), which exactly solve the electronic Schrodinger equation within the space spanned by a 6-31G( *) basis set. Within the D(2h) subgroup used by most electronic structure programs, these states all have the same symmetry ((1)A(g)), and all three states become energetically close for interatomic distances beyond 1.5 A. The quality of several single-reference ab initio methods is assessed by comparison to the benchmark results. Unfortunately, even coupled-cluster theory through perturbative triples using an unrestricted Hartree-Fock reference exhibits large nonparallelity errors (>20 kcal mol(-1)) for the ground state. The excited states are not accurately modeled by any commonly used single-reference method, nor by configuration interaction including full quadruple substitutions. The present benchmarks will be helpful in assessing theoretical methods designed to break bonds in ground and excited electronic states.     

Identification and analysis of the perturbed c3Pi(v=1)-X 1Sigma+ and k 3Pi(v=5)-X 1Sigma+ absorption bands of carbon monoxide

Two new red-degraded bands in the room-temperature vacuum-ultraviolet absorption spectrum of carbon monoxide have been identified in the 94,000-94,500 cm(-1) energy region and analyzed. One of the bands at approximately 94,225 cm(-1) (106.1 nm) has three observable bandheads and is partially overlapped with the strong C 1Sigma+-X 1Sigma+ (1-0) transition at lower energy. It is assigned to the c 3Pi-X 1Sigma+ (1-0) transition. The other band at approximately 94,437 cm(-1) (105.9 nm) with one clear bandhead is assigned to the k 3Pi-X 1Sigma+ (5-0) transition. A strong homogeneous perturbation was found to exist between the two upper states that strongly influences the line positions and shapes of these bands. A rotational deperturbation analysis was performed and molecular rotational constants for both upper states were determined. These deperturbed molecular constants are entirely consistent with the expected values for the k 3Pi valence and c 3Pi Rydberg states. The Hamiltonian interaction term between these two states is found to be separable into vibrational and electronic factors and the electronic factor is determined to be H(e)=323+/-40 cm(-1). A discrepancy in the literature regarding the location of the c 3Pi (v=1) state is identified and discussed.     

Optical observation of the 3s sigma gF3Pi u Rydberg state of N2

Using ultrahigh-resolution 1 XUV+1 UV two-photon ionization laser spectroscopy, the F (3)Pi(u)<--X (1)Sigma(g) (+)(0,0) transition of N(2) has been optically observed for the first time, and the 3s sigma(g)F (3)Pi(u)(upsilon=0) Rydberg level fully characterized with rotational resolution. The experimental spectroscopic parameters and predissociation level widths suggest strong interactions between the F state and the 3p pi(u)G (3)Pi(u) Rydberg and C(') (3)Pi(u) valence states, analogous to those well known in the case of the isoconfigurational (1)Pi(u) states.     

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.     

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.     

Electron correlation in the 3 (1)Sigma(g)+ and 2 (1)Sigma(u)+ excited state lithium molecule

Electron correlation effects in the two excited states of Li(2), 3 (1)Sigma(g) (+) and 2 (1)Sigma(u) (+), one with a shelf shape and another with double minima in their potential energy curves, have been studied with the aid of the calculated electron pair density distribution as a function of the internuclear distance and the analysis of the natural orbitals. Both states show increased electron pair densities at intermediate interelectronic distances around the second minimum of their potential energy curves. Since the bond breaks homolitically this observation runs contrary to regular expectations. Analysis of the electron pair density distributions and the natural orbitals provides mechanisms to account for this abnormal behavior.     

The Zeeman effect and hyperfine interactions in J = 1-0 transitions of CH+ and its isotopologues

The J = 1-0 transitions of (12)CH(+), (13)CH(+), and (12)CD(+) in the ground X(1)Σ(+) state have been unambiguously identified by using an extended negative glow discharge as an ion source. Unexpectedly large Zeeman splittings have been observed, and the (13)CH(+) line exhibits nuclear spin-rotation hyperfine splitting in addition to the Zeeman effect. The nuclear spin-rotation coupling constant was determined to be 1.087(50) MHz for the (13)C species. The rotational g-factor is found to be -7.65(29), in terms of the nuclear magneton for the J = 1 and v = 0 state, more than an order of magnitude larger than values for typical diamagnetic closed shell molecules. These larger than usual magnetic interactions for a (1)Σ molecule are caused by the large rotational energy and relatively small excitation energy of the excited A(1)Π state. The effective g-factor and the spin-rotation coupling constant obtained by ab initio calculations agree very well with the experimentally determined values.     

Completing the 3d metal fluoride series: the pure rotational spectrum of ZnF (X2Sigma+)

The pure rotational spectrum of the ZnF radical has been recorded in the range of 176-527 GHz using millimeter/submillimeter direct absorption techniques. This study is the first gas-phase spectroscopic investigation of this species. Between 5 and 11 transitions were measured for each of five isotopologues of this radical (64ZnF, 66ZnF, 67ZnF, 68ZnF, and 70ZnF) in the ground and several excited vibrational (v=1, 2, and 3) states. Each transition consists of spin-rotation doublets with a splitting of approximately 150 MHz, indicating that the electronic ground state of ZnF is 2Sigma+, as predicted by theory. Fluorine hyperfine splitting was observed in three isotopologues (64ZnF, 66ZnF, and 67ZnF), and hyperfine structure from the zinc-67 nucleus (I=52) was additionally resolved in 67ZnF. Rotational, fine structure, and 19F and 67Zn hyperfine constants were determined for ZnF, as well as equilibrium parameters. The bond length of the main isotopologue 64ZnF was calculated to be re=1.7677 A. Evaluation of the hyperfine constants indicates that the sigma orbital containing the unpaired electron is approximately 80% 4s(Zn) in character with approximately 10% contributions from each of the 2p(F) and 4p(Zn) orbitals. These results imply that ZnF is somewhat less ionic than CaF, as suggested by theory.     

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.     

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).     

Oscillator strength and linewidth measurements of dipole-allowed transitions in 14N2 between 93.5 and 99.5 nm

Line oscillator strengths in 16 electric dipole-allowed bands of 14N2 in the 93.5-99.5 nm (106,950-100,500 cm(-1)) region have been measured at an instrumental resolution of 6.5 x 10(-4) nm (0.7 cm(-1)). The transitions terminate on vibrational levels of the 3psigma 1Sigma u (+), 3ppi 1Pi u, and 3ssigma 1Pi u Rydberg states and of the b' 1Sigma u (+) and b 1Pi u valence states. The J dependences of band f values derived from the experimental line f values are reported as polynomials in J'(J'+1) and are extrapolated to J'=0 in order to facilitate comparisons with results of coupled-Schrodinger-equation calculations that do not take into account rotational interactions. Most bands in this study reveal a marked J dependence of the f values and/or display anomalous P-, Q- and R-branch intensity patterns. These patterns should help inform future spectroscopic models that incorporate rotational effects, and these are critical for the construction of realistic atmospheric radiative transfer models. Linewidth measurements are reported for four bands. Information provided by the J dependences of the experimental linewidths should be of use in the development of a more complete understanding of the predissociation mechanisms in N2.