Lambda Doubling Research Articles

Radiative decay modes of the antiprotonic helium atom

The authors discuss the decay modes of the 'exotic' He atom obtained by replacing one electron in ordinary He by an antiproton. They use the Born-Oppenheimer approximation as a first step in the description of this three-body Coulomb system, and concentrate on states with angular momentum approximately 20 to 40. The authors find that within the Born-Oppenheimer approximation strong correlations between the motion of the antiproton and electron are critical in determining the radiative lifetimes of "vibrationally" excited states. These correlations vastly increase the lifetimes of states formed in the potential determined by the electronic ground state. Going beyond the Born-Oppenheimer approximation, and including states based on excited electronic configurations leads to a new decay mechanism, a radiative transition with simultaneous electron excitation. Surprisingly this is the dominant radiative decay mode for highly excited states of antiprotonic helium. The inclusion of pi states can further alter the picture; strong angular coupling between the 2p sigma and 2p pi states leads to a complete breakdown of the Born-Oppenheimer approximation for states of total angular momentum <or approximately=20 and provides a spectacularly virulent example of Lambda doubling, so strong that the ground vibrational states of angular momentum <or approximately=20 are actually in an excited electronic state well. The auhtors discuss the implications for the long lived states observed experimentally in He.

A 2+1 REMPI study of the E-X transition in CO. Indirect predissociations in the E 1Π state

In this study 2+1 resonance enhanced multiphoton spectra of the E 1Π(v=1, 0)-X 1Σ+(v=0) transitions in 12C16O, 13C16O, 12C18O and 13C18O have been recorded in the laser wavelenght range, 210–216 nm, and rotationally analysed. Perturbations have been observed in both the e and f parity levels of the E 1Π(v=1) state which have the characteristics of an indirect predissociation similar to the well-known accidental predissociation in the Je=31 level of 12C16O (E 1Π, v=0). The present results favour 3Π valence perturbing state which is itself predissociated by a 3Π repulsive state correlating to the lowest dissociation limit; C(3P)+O(3P). Lambda doubling constants for all four isotopes in both the v=0 and v=1 vibrational levels of the E 1Π state have also been obtained.

Rotational, fine, and hyperfine analyses of the (0,0) band of the D 3Π–X 3Δ system of vanadium mononitride

The VN molecule has been produced in a molecular beam apparatus using a laser vaporization source and its D 3Π–X 3Δ(0,0) band has been studied by laser-induced fluorescence at low (∼0.1 cm−1) and sub-Doppler resolution (∼0.004 cm−1). Lifetimes of single rotational levels of the D 3Π0 component have been measured and interpreted. Rotational, fine, and hyperfine structures in six of the nine subbands possible for a 3Π ← 3Δ transition have been recorded. Both states exhibit a rapid transition from case (a) → case (b) coupling cases, manifested by reversals in the Landé patterns of the hyperfine structure. The data have been reduced to a set of 35 molecular constants using a modified case (aβ) effective Hamiltonian in which two additional magnetic hyperfine parameters are required for each state. The distortions in the hyperfine structure are due almost entirely to second-order spin–orbit interaction between states arising from the same configuration. Analysis of the derived parameters indicates that the X 3Δ state is well represented by the single electron configuration ...8σ2 3π4 9σ1 1δ1, in which the 9σ molecular orbital (MO) is a V 4s–4p hybrid (88% V 4s) and the 1δ MO is a pure V 3d orbital; the dominant configuration for the D 3Π state is ...8σ2 3π4 1δ1 4π1, in which the 4π MO is an antibonding orbital composed of at most 82% V 3dπ. The isoconfigurational a 1Δ and e 1Π states are calculated to lie 3390 and 2200 cm−1 above their respective high spin companions. The lambda doubling in the D 3Π0 component has been interpreted in terms of spin–orbit interactions with the B 3Σ− and d 1Σ+ states, both states arising from the ...8σ2 3π4 1δ2 configuration; the d 1Σ+ state is known [Simard, Masoni, and Hackett, J. Mol. Spectrosc. 136, 44 (1989)] to lie 102 cm−1 above D 3Π0, while the B 3Σ− state probably lies about 8000 cm−1 below.

Infrared diode laser spectroscopy of the ground state of GeH (X 2Π1/2)

Transitions in the fundamental band of the ground state X 2Π1/2 of the GeH radical are detected by tunable diode laser spectroscopy. Signals are observed for all five naturally occurring isotopes of germanium. A preliminary fit of the vibrational-rotational constants for the ground state is given, in which the vibrational corrections α A , αγ and α p+2q to the fine structure constant A, the spin rotation constant γ and the lambda doubling constant p + 2q are determined from our data.

2+1 resonantly enhanced multiphoton ionization of CO via the E 1Π–X 1Σ+ transition: From measured ion signals to quantitative population distributions

The 2+1 resonantly enhanced multiphoton ionization (REMPI) spectrum of the CO E 1Π–X 1Σ+ (0,0) transition is used to determine ground state rotational populations with a detection sensitivity of approximately 3×106 molecules per quantum state per cm3. Low rotational states of CO are ionized to CO+; however, high rotational states form both C+ and CO+. This effect is shown to be both branch dependent and J dependent. In order to extract reliable ground state populations, both the C+ and CO+ channels must be measured. When the C+ channel is not accounted for, high rotational states are systematically undercounted. New rotational constants are determined for the C12O16 E 1Π state; Bf0 is 1.9526 cm−1 and Be0 is 1.9645 cm−1. The large lambda doubling (q=0.0119 cm−1 ) of the E state is attributed to a perturbation by the nearby C 1Σ+ state.

Infrared diode-laser spectroscopy of the ground state of SnH (X2Π1/2)

We report the first direct observation of the vibrational-rotational spectrum of the tin hydride radical in its X 2Π1/2 ground state by infrared diode-laser spectroscopy. The isotopic structure, lambda doubling and hyperfine splitting of the tin nucleus have been resolved. A set of effective molecular parameters of the X 2Π1/2 state is given.

The photoexcitation spectrum of the (0, 0, 0) A 2Π u←(1, 0, 0)X 2Π g band of BO 2

The photoexcitation spectrum of the (0, 0, 0) A 2Π u←(1, 0, 0) X 2Π g band of BO 2 has been obtained. A fit to the frequency measurements provided values for the rotational constant, B ν, the centrifugal distortion correction to the rotational and spin-orbit constants, D ν and A dν, respectively, and the lambda doubling constants, p ν and q ν for the excited and ground electronic states. Values for the excited state parameters were measured (in cm −1) to be B ν′=0.31063(7), A dν′=−6.1(6.4)×10 −5, D ν′=1.2(2)×10 −7, p ν′=8.3(5.1)×10 −3, q ν″= 1.7(6)×10 −4. Values for the ground state parameters are B ν″=0.32843(10), A dν″=9.2(8)×10 −4, D ν″=1.5(2.2)×10 −8, p ν″=2.6(6.4)×10 −3, q ν″=6.2(0.7)×10 −4.Since the results revealed high correlation between the excited and ground state parameters, combination difference fits were done in addition to direct fits to the measured transition frequencies. The results indicate that the C( 2Σ g +) state has a significant effect on the lambda doubling.

The e3Σ−-a3Π(0, 0) and E1Σ−-A′1Π(0, 0), (1, 1), and (2, 2) bands of CaO: Multistate deperturbation of the e3Σ−(v = 0) ∼ c3Σ+ (v = 1) ∼ E1Σ− (v = 0) system

The experimental study and analysis of the e3Σ−-a3Π(0, 0) and E1Σ−-A′ 1Π(0, 0), (1, 1), and (2, 2) Orange-Band transitions of CaO are presented along with a deperturbation analysis of the e3Σ− (v = 0) ∼ c3Σ+ (v = 1) ∼ E1Σ− (v = 0) complex of spin-orbit interacting, Aππ−1 configuration, electronic states. Use of laser-induced fluorescence, sub-Doppler intermodulated fluorescence, and optical-optical double-resonance techniques allowed the determination of accurate molecular constants for the e3Σ− (v = 0) and E1Σ− (v = 0, 1, 2) states as well as their common perturber, c3Σ+ (v = 1). Based on an integer-valence, single-atomic-ion configuration, ligand field model of the structure of the low-lying electronic states of CaO, in which the monovalent CaF structure is used as a model for Ca+ localized orbitals and the monovalent NaO structure is used for O− localized orbitals, predictions of several interstate interactions compare favorably with experimentally determined interaction parameters. The discussions of interactions include treatments of diagonal and off-diagonal spin-orbit interactions in Π and Σ electronic states, lambda doubling in 1Π and 3Π states, and fine structure in 3Σ states. Analyses of interactions between O−pσ−1 and pπ−1 configuration states, which differ in re by ∼5%, required the introduction of an empirical factor, Θ, which is interpreted as a measure of hybridization in atomicion orbitals.

Far infrared L.M.R. of[Xtilde]2Π NCO

Pure rotational transitions in the [Xtilde] 2Π3/2 state of the NCO radical have been measured by far infrared laser magnetic resonance (L.M.R.) spectroscopy. Analysis of the Zeeman patterns leads to new determinations of the centrifugal distortion parameters, D and H, the lambda doubling parameter q and the g-factors g r and g′L.

A reanalysis of the molecular beam electric resonance Stark effect data for the a 3Π state of carbon monoxide

The highly precise measurements of Stark coefficients in the lambda doubling transitions of a 3Π CO obtained in previously published molecular beam electric resonance experiments have been reanalyzed. Certain perturbations between vibrational levels of the a 3Π and a′ 3Σ+ states that were neglected in the earlier treatment have been found to be important. An apparent error, by a factor of in the Stark matrix elements that were used in prior work, has also been corrected. The previously reported experimental determination of the dipole moment function of a 3Π CO is shown to be invalid. Thus, the relatively flat appearance of the dipole moment function found in previous ab initio studies may indeed be correct. The dipole moment in the a′ 3Σ+ state and the transition moment between the a 3Π and a′ 3Σ+ states are substantially revised to −0.79 and +0.64 D, respectively.

The microwave spectrum of CO in the a 3Π state. I. The J=0–1 transitions in CO, 13CO, and C18O

The J= 0–1 transitions of a 3Π carbon monoxide have been measured in several isotopic forms and vibrational states: CO (v=0–4), 13CO (v=0–3), and C18O (v=0–4). These new data were combined with the many lambda doublet transition frequencies previously available from the molecular beam electric resonance experiments of Klemperer and co-workers and fit to a model Hamiltonian essentially the same as that used for previously published fits of combined optical–lambda doubling data. Many different fits were made including single state–single isotope, multistate–single isotope, single state–multi-isotope, and multistate–multi-isotope ones. Among the important conclusions are (1) that the explicit perturbation due to the v′=0 level of the a′ 3∑+ state must be included for adequate fits of the v=0–3 data (and of course the more strongly perturbed v=4 data), (2) that the spin–orbit coupling constant A can be determined well from just the microwave–rf data if several isotopic forms are fitted together, and (3) that much additional data is needed for a completely satisfactory characterization of the a 3Π state.

A study of the vibration–rotation and fine structure energy levels of the NSe radical by laser magnetic resonance

Vibration–rotation and fine structure transitions of the NSe radical in its X 2Π state have been studied by CO2 laser magnetic resonance at 11 μm. Transitions involving the five most abundant naturally occurring isotopes of selenium have been detected. These data were all analyzed together by invoking the appropriate isotopic relationships between molecular parameters. The vibrational band origin for N80Se is determined to be 944.542 16(9) cm−1 and the spin–orbit coupling constant à is 891.891 32(11) cm−1. From a consideration of the likely sign of the lambda doubling parameter (p+2q), it is suggested that B electronic state may be 2∑+ rather than 2∑−.

Reaction dynamics of O(1D2)+H2, HD, D2: OH, OD(X 2Πi) product internal energy distributions

Partial internal energy distributions of the hydroxyl reaction products of O(1D)+H2, HD, and D2 reactions are presented. Inverted rotational distributions, preferential population of the π+ lambda doubling sublevels, and statistical population of the spin sublevels are observed. A slight preferential formation of the OD vs OH reaction products observed is measured for the reaction of O(1D)+HD. Surprisal analysis of these results indicates both dynamical and kinematic constraints on the reaction dynamics. Comparison of these results with published model calculations suggest that an insertion mechanism to form a highly energetic collision complex dominates the reaction dynamics.

The rotational spectrum of the C3H radical

The rotational spectrum of the recently discovered C3H radical in both fine-structure ladders of its electronic ground state (X2Pi) with lambda doubling and hyperfine structure has been determined to high accuracy, and the strongest transitions at frequencies less than 376 GHz are tabulated. Recently published spectroscopic constants derived from astronomical and laboratory data (Gottlieb et al., 1985) allowed calculation of the spectrum to a radial velocity of 0.4 km/s at frequencies less than 200 GHz, the uncertainties above being somewhat larger. The hyperfine constants of the sequence of four hydrocarbon radicals CH, C2H, C3H, and C4H are briefly described.

Determination of the strengths of doubled lines by the method of equivalent widths

A technique for the measurement of line strengths of doubled lines using the equivalent width method is developed. The line profile is represented by the Voigt function and the prototype doubling is the lambda doubling in NO. The lambda doubling is incorporated into the algorithm for the theoretical calculations of the equivalent widths. The dependence of the equivalent width on the half width at half intensity, the line strength and splitting is demonstrated. Comparisons of the Voigt, Lorentz and Doppler function properties are included.

The 2–0 band of the A 2Πi ← X 2Σ+ system of SiN near 3.3 μm

The observation and analysis of 187 lines in the 2–0 band of the A 2Πi ← X 2Σ+ system of the SiN radical are described. The 2–0 band, which lies near 3.3 μm, has been recorded with a tunable difference frequency system and discharge amplitude modulation. The analysis gives improved molecular constants for the ground and first excited states, including the first lambda doubling parameters for the A 2Π state.

Lambda doubling in the infrared spectrum of SH

The (1–0), (2–1), and (3–2) infrared vibration–rotation bands of the X2Π ground state of sulfur monohydride were observed in emission from a furnace. Multiplet splitting produces two subbands, each of which exhibits lambda splitting. The band heads were observed for the first time, 285 lines were measured, and a calculation of lambda-doubling parameters was made. The spectrum was recorded using the Fourier transform spectrometer at the National Solar Observatory (Kitt Peak).

A reanalysis of the interstellar CH abundance

view Abstract Citations (58) References (52) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A reanalysis of the interstellar CH abundance. Lien, D. J. Abstract An analysis of historic interstellar CH abundance and electronic state data for the interstellar medium was undertaken to identify the term structures of various electronic states and to identify errors in previous analyses. Attention was devoted to the X(2)Pi, A(2)Delta, B(2)Sigma(-), and C(2)Sigma(+) systems. Error sources were identified as neglect of the Lambda doubling of ground state. The splitting causes a doubling of the oscillator strength of lines from the B-X and C-X electronic systems, blending of two lines appearing as 4300, 3886, and 3143 A lines, the inaccurate identification of which half of the Lambda doublet generated the lines, and no accurate determination of the excitation temperature. Examples are furnished of CH Lambda ground state data from Delta Per, Delta Oph, X Per, and Chi Oph using equivalent widths to show an inverted Lambda doublet, that a radio maser can be detected optically, and a match between the X Per and Delta Per theoretical and measured temperatures. Publication: The Astrophysical Journal Pub Date: September 1984 DOI: 10.1086/162440 Bibcode: 1984ApJ...284..578L Keywords: Abundance; Hydrocarbons; Interstellar Matter; Molecular Spectra; Ultraviolet Astronomy; Line Spectra; Near Ultraviolet Radiation; Oscillator Strengths; Radio Sources (Astronomy); Astrophysics full text sources ADS | data products SIMBAD (4)

The orange arc bands of CaO. Analysis of a D,d 1,3Δ–a 3Π system

The orange and green arc bands of CaO are shown to arise from Ca+ centered (4p,3d)-4s transitions analogous to the CaF A 2Π–X 2Σ+ and B 2Σ+–X 2Σ+ systems. The tremendous complexity of these Ca+O− systems is a consequence of the sixfold degeneracy of the O− p-hole, as compared to the nondegenerate F−(1S). The 0, 0 and 1, 1 bands of a D,d 1,3Δ–a 3Π transition are recorded by intermodulation spectroscopy and assigned (vibration, rotation, absolute parity) by nonstandard techniques. The D 1Δ state is found to lie below the isoconfigurational d 3Δ1 state and D∼d spin-orbit perturbation causes the d 3Δ state to become irregular (3Δ2≳3Δ1≳3Δ3). Two perturbation effects provide the key to the orbital interpretation of the orange and green arc bands: lambda doubling in a 3Π indicates that a π4σσ3Σ+ state lies 1500 cm−1 above a 3Π; D, d 1,3Δ∼B 1Π perturbations suggest recurrence of this 1500 cm−1 interconfigurational splitting which is the O−pσ/pπ splitting induced by the Ca+ ligand.

The nature of the A2Π state in BeF

Ab initio molecular orbital calculations suggest that the A 2 Pi state of BeF is regular, with Lambda doubling constants p and q of the same sign, implying a molecular orbital configuration with a single unpaired pi electron. This is in contrast to the published spectroscopic analysis of the A-X spectrum, which gives p and q of opposite signs, normally associated with inverted Pi electronic states.