Rotationally Resolved Vacuum Ultraviolet Laser Spectra of theCl21Σu←XΣgTransition

Rotationally and isotopically resolved single-photon excitation spectra of jet-cooled Cl₂in the wavelength region between 133 and 138 nm were recorded using a tunable vacuum ultraviolet “laser” generated by two-photon resonantly enhanced four-wave difference mixing in Kr gas. The dominant transition (1¹Σ⁺_u←X¹Σ⁺_g) is well known theoretically and experimentally to involve a double-well excited state potential energy curve formed by a strong homogeneous Rydberg-state/ion-pair state avoided crossing. In this work, single isotopomer spectra were obtained by dispersing and detecting ions produced by (1 + 1′) resonance-enhanced multiphoton ionization in a time-of-flight mass spectrometer. In this way, rotational constants were deduced for the first time for many v′ levels of the least abundant molecular isotope,³⁷Cl₂, which are both localized in the Rydberg well, and delocalized in the ion-pair portion of the 1-state potential energy curve. Our experimentally derived band origins andB^′_vvalues test the practical validity of an analytical 1¹Σ⁺_upotential energy function which is a modified version of the one first proposed by J. Wörmer, T. Möller, J. Stapelfeldt, G. Zimmerer, D. Haaks, S. Kampf, J. Le Calvé, and M. C. Castex (1988. Z. Phys. D,7,383–395).     

High-Resolution Study of the BaI AΠ Electronic State

Near-infrared and visible spectra of the A²Π–X²Σ⁺, C²Π_1/2–A²Π_1/2, C²Π_1/2–B²Σ⁺, and C²Π_1/2–X²Σ⁺ band systems of the BaI molecule were recorded by using Fourier transform spectroscopy (FTS). The spectra were produced from the chemiluminescent reaction Ba + I₂ and also by using laser-induced fluorescence (LIF) technique in which the laser sources were a Ti:sapphire single-mode laser, a dye single-mode laser, and a Kr⁺ multimode ion laser. Resolved rotational data, originating from 19 vibrational levels (0 ≤ v ≤ 5 and 7 ≤ v ≤ 19) of the A²Π state, 24 vibrational levels (0 ≤ v ≤ 18 and 20 ≤ v ≤ 24) of the X²Σ⁺ state, and 8 vibrational levels (1 ≤ v ≤ 2 and 9 ≤ v ≤ 14) of the C²Π state, were used in the final analysis. Previously recorded data for the B²Σ⁺–X²Σ⁺ and C²Π–X²Σ⁺ systems, taken from R. F. Gutterres, J. Vergès, and C. Amiot, J. Mol. Spectrosc. 196, 29–44 (1999) and from C. A. Leach, A. A. Tsekouras, and R. N. Zare, J. Mol. Spectrosc. 153, 59–72 (1992), were added to the present work data field. Accurate and improved molecular constants, for the X²Σ⁺, B²Σ⁺, A²Π, and C²Π states, were derived from a simultaneous treatment of the whole data set.     

The E(4) Πu state in K2 and its perturbations

The E(4) ¹Π_u←X ¹Σ⁺_g band system of the K₂ molecule is investigated by the technique of Doppler-free optical–optical double resonance polarization spectroscopy. The observed vibrational levels v=0 to 9 of the E state are subject to numerous rotational perturbations by the neighboring 4 ³Π_u, 4 ¹Σ⁺_u, and 5 ³Σ⁺_u electronic states. By using deperturbation methods, the potential curves of the 4 ¹Π_u and 4 ³Π_u states are determined as well as some properties of the 4 ¹Σ⁺_u and 5 ³Σ⁺_u state potentials. The results are compared with predictions of ab initio calculations.     

The spectra and structure of indium iodide: The rotational and vibrational constants of the A0 state

The rotational constants of the A0⁺ state of InI are reported for the first time as B_e = 0.038077 cm⁻¹ and α_e = 0.0002373 cm⁻¹, while T_e = 24402.91 cm⁻¹ for the A0⁺-X0⁺ transition. Accurate vibrational constants for both the A0⁺ and X0⁺ states are computed from the derived band origins.     

Laser spectroscopy of LaF: Determination of the separation of the singlet and triplet state manifolds

Tunable dye lasers have been used to excite several known transitions in LaF. Resolved fluorescence spectra obtained after excitation of B¹Π-X¹Σ⁺ and C¹Π-X¹Σ⁺ bands showed transitions to both X¹Σ⁺ and a³Δ states. Analysis of the spectra shows that the state is 1432 cm⁻¹ above X¹Σ⁺, is at 1808 cm⁻¹, and there is an Ω = 2 state (probably ¹Δ) at 5478 cm⁻¹. A new 0⁺-X¹Σ⁺ (v = 0) band has been observed in the vicinity of the B¹Π-X¹Σ⁺ 1-0 band. High resolution excitation spectra of both bands have been obtained, term energies and rotational constants calculated, and the Λ-doubling in B¹Π, v = 1 has been studied. The principal constants (in cm⁻¹) obtained from the analyses wereThe assignments of the low lying states are discussed in terms of their electron configurations and are shown to be in accord with predictions of Ligand Field Theory.     

Rotational vibrational analysis of the BΠ (0) - XΣ band system of BrCl and BrCl

24 bands of the B³Π(0⁺) ← X¹Σ⁺ system of ⁷⁹Br³⁵Cl and ⁸¹Br³⁵Cl have been photographed at high resolution. Direct least-mean square fits of the measured line frequencies were made to determine band origins and rotational constants in the ranges 1 ≤ v″ ≤ 7, 2 ≤ v′ ≤ 8. A reiterative procedure was adopted in which the higher order centrifugal distortion constants (D_v, H_v) were constrained to theoretical values calculated from RKR potential curves. The results of the analysis are used to obtain a set of Franck-Condon factors and r-centroids for the B-X system of BrCl.     

A spectroscopic study of the D(0u+) ion-pair state of Br2 by the optical-optical double-resonance technique

An optical-optical double-resonance technique has been applied to study the D(0_u⁺) ion-pair state of Br₂ in a one-photon resonant three-photon absorption. The OODR transition proceeds through the high vibrational level of the B³Π(0_u⁺) state, which compromises a large Franck-Condon shift required for the excitation of Br₂ from the X¹Σ_g⁺ state to the D(0_u⁺) state. Dunham parameters of the D(0_u⁺) state, based on a global least-squares fit of 407 transitions (v′ = 0–16, J′ = 17–115), are Y₀₀ = 49928.443(41), Y₁₀ = 134.467(19), Y₂₀ = ?8.71(27) × 10^?2, Y₃₀ = ?3.36(10) × 10^?3, Y₀₁ = 4.2382(15) × 10^?2, Y₁₁ = ?1.061(36) × 10^?4, Y₂₁ = ?2.00(27) × 10^?6, and Y₀₂ = ?1.93(11) × 10^?8 for ⁷⁹Br₂ (all in cm^?1, and 3σ in parentheses). The single rovibronic fluorescence spectrum of the D(0_u⁺) state shows a transition terminating on the X¹Σ_g⁺ ground state, and establishes the absolute v′ numbering on the basis of the Franck-Condon factor calculations. The v′ = 2 and 3 levels of the D(0_u⁺) state are strongly perturbed due to the heterogeneous interaction with the 1_u state correlating with the same ionic products of the D(0_u⁺) state at the dissociation limit, $\text{Br}{}^{\mathrm{?}}\text{(}{}^1\text{S) +}\text{Br}{}^{\mathrm{+}}\text{(}{}^3\text{P}{}_2\text{)}$.     

Laser-induced fluorescence of Na2 at the Na(3s → 5s) two-photon transition (6022.3 Å)

Na₂ excited from the X¹Σ_g⁺ state to the A¹Σ_u⁺ state by a narrow band (3 MHz) Rhodamine-6G dye laser at 6022.3 Å, the same wavelength at which Na undergoes the 3s–5s two-photon transition, gives four fluorescence series from A¹Σ_u⁺ levels (v′ = 21, J′ = 26), (18, 33), (33, 19), and (34, 50). The last two series are much weaker in intensity, and at long wavelengths many doublets are lost in the background noise. The same (34, 50) fluorescence series was found by other workers in the lab using a Kr⁺ (5682 Å) laser as excitation source. Their analysis agrees very well with the findings in the work.     

Electron-vibrational energy exchange in collisions of Ar atoms in the 3P2 metastable state with N2(X1S g+ ) molecules

Rate constants for electron-vibrational energy exchange Ar(³ P ₂) + N₂(X ¹Σ _g ⁺, ν = 0) → Ar(¹ S ₀) + N₂(C ³Π _u , ν′), where ν′ = 0, 1, 2, were calculated. Calculations were performed taking into account the presence of a resonance in electron scattering by N₂(X ¹Σ _g ⁺). As a result, the interaction of Ar(³ P ₂) with N₂(X ¹Σ _g ⁺, ν = 0) was characterized by attraction and, in the end, intersection of electron-vibrational potential surfaces correlating with Ar(³ P ₂) + N₂(X ¹Σ _g ⁺, ν = 0) and Ar(¹ S ₀) + N₂(C ³Π _u , ν′) at interparticle distances of 2.5–3.5 ?. Exchange interaction at which electron-vibrational transitions in the region of intersection of electron-vibrational transitions in the region of intersection of electron-vibrational potential surfaces accompanied by spin exchange were induced was calculated by the asymptotic method. The rate constants determined at 300–600 K were on the order of 10⁻¹¹−10⁻¹² cm³/s and weakly increased as the temperature grew. Mainly the C ³Π _u , ν′ = 0 state of the N₂ molecule was populated. The calculation results were in satisfactory agreement with the experimental data obtained at 300 K.     

Predissociation linewidths and oscillator strengths for the (2-0) to (13-0) Schumann-Runge bands of O2

Analysis of the absorption spectrum of O₂ in the Schumann-Runge bands (B³Σ_u^?-X³Σ_g^?) from the 2-0 to the 13-0 band yields oscillator strengths which are in good agreement with past theoretical calculations. Predissociation linewidths deduced from the data tend to be larger than theoretical predictions for v′ ≤ 5 and are reasonably near theory for v′ > 5. The qualitative dependence of the linewidths on vibrational level is in accord with that expected for a repulsive potential intersecting the B³Σ state near v′ = 4. For a given band the predissociation linewidth deduced from the spectra tends to increase as the total angular momentum increases. The new linewidths are smaller than some past experimental results, and this will have an impact on future calculations of the photodissociation rates of O₂, NO, and H₂O in the earth's upper atmosphere.     

Measurement of Vcb from the decay process

A new precise measurement of |V_cb| and of the branching ratio BR ) has been performed using a sample of about 5000 semileptonic decays , selected by the DELPHI detector at LEP I by tagging the soft pion from D^*+→D⁰π⁺. The results are: V_cb=(39.0±1.5 (stat.)^+2.5_−2.6 (syst. exp.)±1.3 (syst. th.))×10⁻³,

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. The analytic dependencies of the differential cross-section and of the Isgur–Wise form factor as functions of the variable w=v_B⁰·v_D^* have also been obtained by unfolding the experimental resolution.     

The electronic spectrum of bismuth monofluoride: A reinvestigation of the A0-X10 system

A reinvestigation of the A0⁺-X₁0⁺ band system, the most electronic transitions reported for bismuth monofluoride, is presented. Approximately 65 bands were photographed in emission between 4220 and 5417 Å, of which 33 were rotationally analyzed. Inconsistencies in earlier vibrational analyses were resolved. Rotational constants for 0 ≤ ν′ ≤ 12 and 0 ≤ ν″ ≤ 18 were determined from direct least-squares fitting to the measured line positions of each band. “Merging” of the overdetermined constants was performed to obtain the best single estimate of each parameter. The resulting minimum-variance linear unbiased estimates were used to calculate RKR potential curves. Franck-Condon factors and r centroids were subsequently obtained and are presented. Evidence is given for predissociation in the upper state; perturbations involving levels above the crossing point are correlated with those previously reported in the B0⁺ state. The upper limit of the ground-state dissociation energy (3.14 eV) is in accord with extrapolated values as given in earlier investigations. The nature of a postulated third interacting state is also discussed.     

Fourier Transform Spectroscopy of theYΣ–XΠiTransition of CuO

TheY²Σ⁺–X²Π_inear-infrared electronic transition of CuO was observed at high resolution for the first time. The spectrum was recorded with the Fourier transform spectrometer associated with the McMath–Pierce Solar Telescope at Kitt Peak. The excited CuO molecules were produced in a low pressure copper hollow cathode sputter with a slow flow of oxygen. Constants for theY²Σ⁺states of CuO are:T₀= 7715.47765(54) cm⁻¹,B= 0.4735780(28) cm⁻¹,D= 0.822(12) × 10⁻⁶cm⁻¹,H= 0.46(10) × 10⁻¹⁰cm⁻¹, γ = −0.089587(42) cm⁻¹, γ_D= 0.1272(79) × 10⁻⁶cm⁻¹,b_F= 0.12347(22) cm⁻¹, andc= 0.0550(74) cm⁻¹. ImprovedX²Π_iconstants are also presented.     

The bΣ(b0) → XΣ(X10,X21) and aΔ(a2) → X21 transitions of AsBr

Emission spectra of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺,X₂1) and a¹Δ(a2) → X₂1 transitions of AsBr have been measured in the near-infrared spectral region with a Fourier-transform spectrometer. The arsenic bromide radicals were generated in fast-flow systems by reaction of arsenic vapor (As_x) with bromine and were excited by microwave-discharged oxygen. The most prominent features in the spectrum are the Δv = +1,0,−1, and −2 band sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺) transition in the range 11 700-12 700 cm⁻¹. With lower intensities, the Δv = 0 and −1 sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₂1) sub-system show up in the same range. Further to the red, between 6000 and 6700 cm⁻¹, the Δv = 0, +1, and −1 sequences of the hitherto unknown a¹Δ(a2) → X₂1 transition are observed. Analyses of medium- and high-resolution spectra have yielded improved molecular constants for the X₁0⁺, X₂1, and b0⁺ states and first values of the electronic energy and the vibrational constants of the a2 state.     

The AΠu state of : Electric properties, fine and hyperfine coupling constants, and magnetic moments (g-factors). A theoretical study

Several properties are calculated for A²Π_u of —the majority for the first time—including electric and magnetic moments, and fine/hyperfine structure (fs/hfs) parameters. The new results are compared with our previous ones for X² and B² of [P.J. Bruna, F. Grein, J. Mol. Spectrosc. 227 (2004) 67–80]. The electric quadrupole Θ and hexadecapole Φ moments, polarizability α, and hfs constants a, b, c, d, eQq₀, eQq₂ are evaluated at the density functional theory (DFT) level [B3LYP/aug-cc-pVQZ]. The fs constants (spin–orbit coupling A_Π, Λ-doubling p, q, spin-rotation γ_Π), and magnetic moments (g-factors) are obtained via 2nd-order sum-over-states expansions, using wavefunctions and matrix elements obtained with a multireference configuration interaction (MRDCI) method, and the Breit–Pauli Hamiltonian. At equilibrium, 2nd-order properties of A²Π_u are dominated by its coupling with B². For the A state, two independent components are reported for traceless tensor properties (multipoles Θ and Φ; hfs parameters c/d and q₀/q₂) and three for traced properties (polarizability α and g-factors), i.e., one more component than for axially symmetric Σ states. The currently available experimental data on — limited to A_Π, p, and q—are well reproduced by our theoretical results.     

Deperturbation of the N2+ first negative group B2Σu+-X2Σg+

Twelve bands of the N₂⁺B²Σ_u⁺-X²Σ_g⁺ system, including v_B = 0–6 and v_X = 0–8, are reanalyzed. All effects of B²Σ_u⁺ ～ A²Π_u perturbations are explicitly considered. Despite the use of high precision (0.01 cm^?1) line measurements, no evidence for a perturber other than A²Π_u is obtained. Deperturbed constants for the B²Σ_u⁺ and X²Σ_g⁺ states are derived. The deperturbation is shown to be self-consistent and complete (excluding effects of the C²Σ_u⁺ state) by examining semiempirical relationships of the perturbation matrix elements with the spin-rotation constants of the B and X states and atomic spin-orbit parameters. A number of previous analyses of transitions involving the v_B = 3 and 5 levels are found to be incorrect.     

Laser magnetic resonance of the O2 molecule at 699 μm

A new highly sensitive far infrared optically pumped laser magnetic resonance (LMR) spectrometer has facilitated the observation of 21 transitions in O₂ at 699 μm (428.6285 GHz). All of these transitions involve N = 3 ← 1 of the oxygen molecule in its electronic ground state, X³Σ_g⁻. Of these 21 lines, 10 are due to the ¹⁶O₂, v = 0; 5 are due to the ¹⁶O₂, v = 1; 5 are due to the ¹⁶O¹⁸O, v = 0; and 1 set of 6 hyperfine components is due to the ¹⁶O¹⁷O, v = 0. From the intensity of the observed lines the sensitivity limit of this LMR spectrometer is found to be about 10⁻⁹ cm⁻¹ at this frequency with a 1-sec time constant.     

Line strength measurements of carbonyl sulfide (OCS) in the 2v3, v1+2v2+v3, and 4v2+v3 bands

To support planetary studies of the Venus atmosphere, we measured line strengths of the 2v₃, v₁+2v₂+v₃, and 4v₂+v₃ bands of the primary isotopologue of carbonyl sulfide (¹⁶O¹²C³²S), whose band centers are located at 4101.387, 3937.427, and 4141.212 cm⁻¹, respectively. For this, infrared absorption spectra in normal carbonyl sulfide (OCS) sample gas were recorded at an unapodized resolution of 0.0033 cm⁻¹ at ambient room temperatures using a Bruker Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory. The FTS instrumental line shape (ILS) function was investigated, which revealed no significant instrumental line broadening or distortions. Various custom-made short cells and a multi-pass White cell were employed to achieve optical densities sufficient to observe the strong 2v₃ and the weaker bands in the region. Gas sample impurities and the isotopic abundances were determined from mass spectrum analysis. Line strengths were retrieved spectrum by spectrum using a non-linear curve fitting algorithm adopting a standard Voigt line profile, from which Herman–Wallis factors were derived for the three bands. The band strengths of 2v₃, v₁+2v₂+v₃, and 4v₂+v₃ of ¹⁶O¹²C³²S (normalized at 100% of isotopologue) are observed to be 6.315(13)×10⁻¹⁹, 1.570(2)×10⁻²⁰, and 7.949(20)×10⁻²¹ cm⁻¹/molecule cm⁻², respectively, at 296 K. These results are compared with earlier measurements and the HITRAN 2004 database.     

nπ transitions in crystals of tetramethyl-1,3-cyclobutanedione-h12 and -d12

The polarized low-temperature crystal absorption spectra of tetramethyl-1,3-cyclobutanedione-h₁₂ and -d₁₂ have been measured from 25 000–40 000 cm⁻¹, and nπ^* excited states identified as follows: ³A_u with origin (-h₁₂/-d₁₂) at (25 720/25 780)cm⁻¹; ¹A_u at (27 130/27 173)cm⁻¹; two ¹B_1g states with origins near 32 000 cm⁻¹. Excitation is accompanied by distortion of the ring and a slight lengthening of the CO bonds, but the carbonyl groups remain planar. Surprisingly, CH/CD-stretching vibrations in the substituent methyl groups are active in intensity borrowing.     

High-Resolution Laser Spectroscopy of YbCl: The AΠ–XΣ Transition

The A²Π–X²Σ⁺ transition of ¹⁷⁴Yb³⁵Cl and ¹⁷²Yb³⁵Cl has been rotationally analyzed for the first time. Doppler-limited laser excitation spectroscopy with selective detection of fluorescence was used to obtain spectra of the 0–0 and 1–0 bands with a measurement accuracy of approximately 0.0035 cm⁻¹. Resolved fluorescence was used to record the 0–1, 0–2, and 0–3 bands and to unequivocally assign the rotational numbering, N, to the laser excitation spectra. In total, over 1300 line positions have been measured and assigned for each of the two isotopomers and employed in least-squares fits of molecular parameters. The principal results for the A²Π state are A_e = 1491.494(2) cm⁻¹ and R_e = 2.4433(1) Å, and for the X²Σ⁺ state, R_e = 2.4883(2) Å and γ_e = 4.59(2) × 10⁻³ cm⁻¹. The interaction between the X²Σ⁺ and A²Π states has been investigated and is shown to be the main contributor to the spin–rotation splitting in the ground state.