M. Dulick

Line Intensities and Molecular Opacities of the FeH F 4Δi-X 4Δi Transition

We calculate new line lists and opacities for the F 4 Di-X 4 Di transition of FeH. The 0-0 band of this transition is responsible for the Wing-Ford band seen in M-type stars, sunspots, and brown dwarfs. The new Einstein A-values for each line are based on a high-level ab initio calculation of the electronic transition dipole moment. The necessary rotational line strength factors (Honl-London factors) are derived for both the Hunds case (a) and (b) coupling limits. A new set of spectroscopic constants was derived from the exist- ing FeH term values for v¼ 0, 1, and 2 levels of the X and F states. Using these constants, extrapolated term values were generated for v¼ 3 and 4 and for J-values up to 50.5. The line lists (including Einstein A-values) for the 25 vibrational bands with v� 4 were generated using a merged list of experimental and extrapolated term values. The FeH line lists were used to compute the molecular opacities for a range of temperatures and pressures encountered in L and M dwarf atmospheres. Good agreement was found between the computed and observed spectral energy distribution of the L5 dwarf 2MASS-1507. Subject headings: infrared: stars — line: identification — molecular data — stars: atmospheres — stars: fundamental parameters — stars: low-mass, brown dwarfs

Electronic states of the CeO molecule: Absorption, emission, and laser spectroscopy

Abstract The electronic spectrum of the CeO molecule is characterized by the existence of many 0-0 bands resulting from transitions between various Ω components of excited states and the 16 lower Ω states which arise from the lowest configuration… (4f)(6s). Classical studies of rotational structure of absorption and emission spectra have been extended, and argon-ion and tunable dye (coumarin 460, rhodamine 6G, rhodamine 101) lasers have been used to excite known transitions in bands which had previously been rotationally analyzed. The resulting fluorescence spectra have been used to establish the relative energies of the lower states. By tuning the lasers to excite analyzed transitions from different known electronic states it has been possible to determine the energies of 16 low-lying states, to assign quantum numbers to 14 with certainty, and to suggest assignments for the other 2. The resulting energy level diagram of lower states is discussed and shown to correlate well with the 4f6s configuration of the Ce2+ ion. From the energies of the low-lying states, those of the higher excited states are calculated and in some cases new values of vibrational and rotational constants are derived.

Laser excited fluorescence of CS2

Abstract Resonance fluorescence excited by ultraviolet lines of argon and krypton ion lasers has been observed from carbon disulfide. The strongest excitations are to single rotational levels within bands of Klemans R system having K = 0 and 1. Fluorescence in each instance forms a long progression in the ground-state bending vibration, ν ″ 2 . Vibrational levels as high as (1,28°,0) have been identified.

The A 3Φ -X 3Δ System (γ Bands) of TiO: Laboratory and Sunspot Measurements

The spectrum of the A3Φ-X3Δ system of TiO has been measured in the laboratory as well as in sunspots. In the laboratory, the bands were excited in a hollow cathode lamp and were observed using a Fourier transform spectrometer. These bands were also identified in the spectrum of a sunspot umbra recorded with the same spectrometer. Both laboratory and solar measurements have been combined with jet-cooled laser measurements and pure rotational frequencies in the X3Δ ground state to obtain improved molecular constants for the A3Φ and X3Δ states of TiO. RKR potential energy curves and Franck-Condon factors were also calculated.

Electronic structure of PrO: an analysis summary

Abstract The (0,0) bands of nine prominent electronic transitions, Systems X, XI, and XVI through XXII, in the wavelength region 500–800 nm were studied. High-precision (±0.005 cm −1 ), Doppler-limited, selectively detected cw-dye laser fluorescence excitation spectra for Systems XVI through XXII were recorded and analyzed. Definitive Ω assignments for the upper and lower states of these transitions were established from identified first lines in the P and R branches. Resolved fluorescence studies revealed 22 additional electronic transitions in the same wavelength region, many of which provide energy linkages between the upper or lower states of previously observed transitions. The comprehensive energy level diagram assembled from 31 electronic transition linkages comprises a total of 22 upper and lower electronic levels. Ω assignments and relative energies for the electronic states of the transitions studied (including Systems XIV and IX identified in fluorescence and the proposed assignment for System VI) are System Ω′ T′ 0 ( cm −1 ) Ω″ T″ 0 ( cm −1 ) VI 5.5 11102 4.5 2157 IX 4.5 16597 3.5 3887 X 5.5 13259 4.5 220 XI 5.5 13865 4.5 220 XIV 5.5 16595 4.5 2157 XVI 5.5 19169 4.5 3720 XVII 4.5 16597 3.5 0 XVIII 7.5 21321 6.5 3965 XIX 6.5 19687 5.5 2111 XX 5.5 18069 4.5 220 XXI 4.5 18885 4.5 220 XXII 5.5 19169 4.5 220 The relative energies are with respect to the lower state of System XVII, assigned here as the ground electronic state.

SPECTROSCOPIC CONSTANTS, ABUNDANCES, AND OPACITIES OF THE TiH MOLECULE

Using previous measurements and quantum chemical calculations to derive the molecular properties of the TiH molecule, we obtain new values for its rovibrational constants, thermochemical data, spectral line lists, line strengths, and absorption opacities. Furthermore, we calculate the abundance of TiH in M and L dwarf atmospheres and conclude that it is much higher than previously thought. We find that the TiH/TiO ratio increases strongly with decreasing metallicity, and at high temperatures can exceed unity. We suggest that, particularly for subdwarf L and M dwarfs, spectral features of TiH near ~0.52 and 0.94 μm and in the H band may be more easily measurable than heretofore thought. The recent possible identification in the L subdwarf 2MASS J0532 of the 0.94 μm feature of TiH is in keeping with this expectation. We speculate that looking for TiH in other dwarfs and subdwarfs will shed light on the distinctive titanium chemistry of the atmospheres of substellar-mass objects and the dimmest stars.

The electronic structure of LaF: A multiconfiguration ligand field calculation

A zero‐free‐parameter ligand field model is used to account for the observed low‐lying (E<10 000 cm−1) electronic states of LaF. The electronic structure of LaF is represented as the effect of a nonpolarizable point F− ligand on the two valence electrons of a free La+ atomic ion. Free‐ion configuration interaction (CI) effects (represented by a parametric fit of the free La+ energy levels to Fk,Gk Slater–Condon electrostatic and ζ spin–orbit parameters) and ligand‐driven CI (treated by Bk0 ligand field radial integrals evaluated using Hartree–Fock La+ orbitals) are included in the model. A series of calculations is described, from the simplest ‘‘primitive LFT model’’ which includes the three lowest‐lying and most important configurations (6s2, 5d6s, 5d2) to the most elaborate ‘‘balanced s‐polarized LFT model’’ which includes six configurations (6s2, 5d6s, 5d2, 6s6p, 5d6p, and 6p2) in order to account properly for s–p polarization effects. The inclusion of ligand‐driven CI (metal‐centered orbital polarizat...

Low lying electronic states of CeO

A summary is given of the results of laser induced fluorescence experiments on the CeO molecule, which result in the determination of the relative energies of seven low lying electronic states. Both argon ion and cw dye lasers were used to excite several transitions from the X1(Ω=2), X2(Ω=3), and X3(Ω=4) states and the resulting fluorescence spectra showed that (i) the X2(3) state is 80.4±0.7 cm−1 above X1(2), (ii) X4(3) is 100.6±1.5 cm−1 above X3(4), and (iii) there are three states labeled u(2), w(3), v(2), which are 834, 2537, and 2688 (±3) cm−1 respectively above X2(3). It was also shown that the vibrational frequencies ΔG1/2, of the seven low lying states are all between 820 and 825 cm−1.

Laser spectroscopy of YbO: Observation and analysis of some 0+-1Σ+ transitions

Abstract Argon ion and tunable dye lasers have been used to excite different transitions in YbO. Resolved fluorescence spectra have resulted in the observation of three low lying states. Long progressions were observed in the lowest state and vibrational constants have been calculated. High resolution excitation spectra of three bands in the rhodamine 6G region have been obtained and their rotational and isotopic structure (Yb has six isotopes) analyzed. The three bands are all shown to be 0+-1Σ+ transitions where the 1Σ+ state is the lowest observed state of the molecule. Term energies and rotational constants have been determined for each state and the vibrational spacing Δ G 1 2 of the lower state has been calculated. For each state, the isotopic change in constants has been discussed and compared with theory. The isotope effect has been used to determine the vibrational numbering of the upper states and to estimate their vibrational constants. The ligand field theoretical (LFT) model for rare earth oxides is outlined and its predictions for YbO are discussed. The assignment and vibrational frequency of the lowest state are shown to be in accord with the LFT predictions. The principal constants (in cm−1) determined for 174YbO are lowest state (1Σ+): Be = 0.35236(6), αe = 0.00428(6), Δ G 1 2 = 683.107(1) ; upper state A(v = 4); T4 = 17254.584(1), B4 = 0.29296(4), ωe = 547(20); upper state B(v = 2): T2 = 16475.002(1), B2 = 0.29493(4), ωe = 585(20).

Sub‐Doppler Zeeman spectroscopy of the CeO molecule

Sub‐Doppler Zeeman spectra of several low‐J rotational lines in 0–0 bands of CeO[16.5]2–X12, [16.5]4–X23, [18.4]4–X34, and [19.3]3–X43 systems have been recorded by intermodulated fluorescence spectroscopy. Electronic g values for the four lower states [the Ω=Ja states of the Ce+2(4 f 6s)O−2] superconfiguration obtained from Zeeman splittings of low‐J lines at magnetic fields up to 1100 G, are found to agree with g values calculated from the eigenvectors of a ligand field effective Hamiltonian. The present results demonstrate the capability of the ligand field model to predict electronic properties in addition to energies and illustrate the value of the Zeeman effect for uncovering the atomic–ion quantum numbers which are not normally specified for molecules in the strong spin‐orbit [Hund’s case (c)] limit.