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Scandium monocarbide molecules, ScC, have been prepared by the reaction of 532 nm laser-ablated Sc metal with acetylene or methane under supersonic jet-cooled conditions. Electronic spectra of Sc12C and Sc13C have been recorded in the region 14 140–16 000 cm−1 using laser-induced fluorescence, and about 40 bands of each isotopomer have been analyzed rotationally. Wavelength resolved emission spectra have been obtained for many of them. The results show that Sc12C has a 2Πi ground state, with a bond length of 1.952 Å. Its vibrational frequency and spin-orbit coupling constant are 648 cm−1 and −39.47 cm−1, respectively (631 cm−1 and −39.32 cm−1 in Sc13C). Lying 155.58 cm−1 above the X2Π3/2 level (154.72 cm−1 in Sc13C) is a 4Π5/2 level, the lowest spin-orbit component of a 4Πi state. The excited states at higher energy are very complicated. Bands from both the doublet and quartet spin manifolds are present, and there are strong doublet-quartet interactions which induce many nominally-forbidden bands violating the selection rule ΔS = 0. Eight excited electronic states have been recognized, including four 4Δ states. These 4Δ states represent four of the five 4Δ states from the electron configurations (C 2pσ)2 (C 2pπ)2 (Sc 3dδ)1 and (C 2pσ)1 (C 2pπ)2 (Sc 4sσ)1 (Sc 3dδ)1. [ABSTRACT FROM AUTHOR]

Scandium monocarbide molecules, ScC, have been prepared by the reaction of 532 nm laser-ablated Sc metal with acetylene or methane under supersonic jet-cooled conditions. Electronic spectra of Sc12C and Sc13C have been recorded in the region 14 140–16 000 cm−1 using laser-induced fluorescence, and about 40 bands of each isotopomer have been analyzed rotationally. Wavelength resolved emission spectra have been obtained for many of them. The results show that Sc12C has a 2Πi ground state, with a bond length of 1.952 Å. Its vibrational frequency and spin-orbit coupling constant are 648 cm−1 and −39.47 cm−1, respectively (631 cm−1 and −39.32 cm−1 in Sc13C). Lying 155.58 cm−1 above the X2Π3/2 level (154.72 cm−1 in Sc13C) is a 4Π5/2 level, the lowest spin-orbit component of a 4Πi state. The excited states at higher energy are very complicated. Bands from both the doublet and quartet spin manifolds are present, and there are strong doublet-quartet interactions which induce many nominally-forbidden bands violating the selection rule ΔS = 0. Eight excited electronic states have been recognized, including four 4Δ states. These 4Δ states represent four of the five 4Δ states from the electron configurations (C 2pσ)2 (C 2pπ)2 (Sc 3dδ)1 and (C 2pσ)1 (C 2pπ)2 (Sc 4sσ)1 (Sc 3dδ)1. [ABSTRACT FROM AUTHOR]

Perturbations in the K = 1 and 3 levels of the [A.sup.1][A.sup.u], [4v.sub.3] state of acetylene are explained as interactions with levels of the [A.sup.1][A.sub.u], [3.sup.1][B.sup.4] ([v.sub.3] = 1, [v.sub.4] + [v.sub.6] = 4) polyad. A satisfactory leastsquares fit to the perturbed level structure has been obtained, treating the [4v.sub.3] state as an asymmetric top perturbed by isolated K = 1 and 3 levels. Accurate deperturbed rotational constants for the interacting states are presented. PACS No: 33.20.Lg Les perturbations dans les niveaux K = 1 et 3 de l'etat [A.sup.][A.sub.u], [4v.sup.3] de l'acetylene sont expliquees comme etant des interactions avec le polyade [A.sup.1][A.sub.u], [3.sup.1][B.sup.4] ([v.sub.3] = 1, [v.sub.4] + [v.sub.6] = 4). Nous obtenons un ajustement satisfaisant par moindres carres pour la structure des niveaux perturbes, en traitant l'etat [4v.sub.3] comme une toupie asymetrique perturbee par les niveaux isoles K = 1 et K = 3. Nous presentons des valeurs precises libres de perturbation des constantes rotationnelles pour les niveaux en interaction. [Traduit par la Redaction], 1. Introduction The [A.sup.1][A.sub.u] state of acetylene is one of the most widely studied of all excited electronic states of a polyatomic molecule. It is important for the information it [...]

The region 1273-1290 cm-1 of the ν4 fundamental of the simplest Criegee intermediate, CH2OO, has been measured using a quantum cascade laser transient absorption spectrometer, which offers greater sensitivity and spectral resolution (<0.004 cm-1) than previous works based on thermal light sources. Gas phase CH2OO was generated from the reaction of CH2I + O2 at 298 K and 4 Torr. The analysis of the absorption spectrum has provided precise values for the vibrational frequency and the rotational constants, with fitting errors of a few MHz. The determined ratios of the rotational constants, A'/A" = 0.9986, B'/B" = 0.9974, and C'/C" = 1.0010 and the relative intensities of the a- and b-type transitions, 90:10, are in good agreement with literature values from a theoretical calculation using theMULTIMODE approach, based on a high-level ab initio potential energy surface. The low-K (=Ka) lines can be fitted extremely well, but rotational perturbations by other vibrational modes disrupt the structure for K = 4 and K ⩾ 6. Not only the spectral resolution but also the detection sensitivity of CH2OO IR transitions has been greatly improved in this work, allowing for unambiguous monitoring of CH2OO in kinetic studies at low concentrations [ABSTRACT FROM AUTHOR]

The region 1273-1290 cm-1 of the ν4 fundamental of the simplest Criegee intermediate, CH2OO, has been measured using a quantum cascade laser transient absorption spectrometer, which offers greater sensitivity and spectral resolution (<0.004 cm-1) than previous works based on thermal light sources. Gas phase CH2OO was generated from the reaction of CH2I + O2 at 298 K and 4 Torr. The analysis of the absorption spectrum has provided precise values for the vibrational frequency and the rotational constants, with fitting errors of a few MHz. The determined ratios of the rotational constants, A'/A" = 0.9986, B'/B" = 0.9974, and C'/C" = 1.0010 and the relative intensities of the a- and b-type transitions, 90:10, are in good agreement with literature values from a theoretical calculation using theMULTIMODE approach, based on a high-level ab initio potential energy surface. The low-K (=Ka) lines can be fitted extremely well, but rotational perturbations by other vibrational modes disrupt the structure for K = 4 and K ⩾ 6. Not only the spectral resolution but also the detection sensitivity of CH2OO IR transitions has been greatly improved in this work, allowing for unambiguous monitoring of CH2OO in kinetic studies at low concentrations [ABSTRACT FROM AUTHOR]

Rydberg states of calcium monofluoride in the n* = 17-20 region have been observed by ionization-detected optical--optical double-resonance spectroscopy via the [D.sup.2][[SIGMA].sup.+] v = 1 intermediate state. All members of the six core-penetrating Rydberg series in the n* = 17-20 region and several components of the 17f and 17g core-nonpenetrating Rydberg states have been assigned. While the assignment of core-penetrating Rydberg states is straightforward without use of an effective Hamiltonian model, "spectrum-only" assignment of core-nonpenetrating states is complicated because strong l-uncoupling causes the core-nonpenetrating stores to evolve rapidly from Hund's case (b) to Hund's case (d) coupling. We describe "spectrum-only" assignment procedures, developed in the spirit of Gerhard Herzberg, that can be used to assign optical-optical double-resonance spectra of core-penetrating and core-nonpenetrating Rydberg states using only information contained in the spectrum rather than predictions derived from an effective Hamiltonian model. The ambiguities that arise in the assignment of each class of states are discussed in detail. Key words: CaF, etectric quadrupole moment, Rydberg states, laser spectroscopy.

Rotational analyses have been carried out for four of the strongest bands of the à - X transition of the C3Ar van der Waals complex, at 393 and 399 nm. These bands lie near the 02-0-000 and 04-0-000 bands of the Ã1Πu- X1Σ+ g transition of C3 and form two close pairs, each consisting of a type A and a type C band of an asymmetric top, about 4 cm-1 apart. Only K" = even lines are found, showing that the complex has two equivalent carbon atoms (I = 0), and must be T-shaped, or nearly so. Strong a- and b-axis electronic-rotational (Coriolis) coupling occurs between the upper states of a pair, since they correlate with a 1Πu vibronic state of C3, where the degeneracy is lifted in the lower symmetry of the complex. Least squares rotational fits, including the coupling, have given the rotational constants for both electronic states: the van der Waals bond lengths are 3.81 and 3.755 Ã, respectively, in the ground and excited electronic states. For the ground state our new quantum chemical calculations, using the Multi-Channel Time-Dependent Hartree method, indicate that the C3 unit is non-linear, and that the complex does not have a rigid-molecule structure, existing instead as a superposition of arrowhead (↑) and distorted Y-shaped (Y) structures. [ABSTRACT FROM AUTHOR]

We report novel experimental strategies that should prove instrumental in extending the vibrational and rotational assignments of the S1 state of acetylene, C2H2, in the region of the cis-trans isomerization barrier. At present, the assignments are essentially complete up to ∼500 cm-1 below the barrier. Two difficulties arise when the assignments are continued to higher energies. One is that predissociation into C2H + H sets in roughly 1100 cm-1 below the barrier; the resulting quenching of laser-induced fluorescence (LIF) reduces its value for recording spectra in this region. The other difficulty is that tunneling through the barrier causes a staggering in the K-rotational structure of isomerizing vibrational levels. The assignment of these levels requires data for K values up to at least 3. Given the rotational selection rule K′ - ℓ′′ = ± 1, such data must be obtained via excited vibrational levels of the ground state with ℓ′′ > 0. In this paper, high resolution H-atom resonance-enhanced multiphoton ionization spectra are demonstrated to contain predissociated bands which are almost invisible in LIF spectra, while preliminary data using a hyperthermal pulsed nozzle show that ℓ′′ = 2 states can be selectively populated in a jet, giving access to K′ = 3 states in IR-UV double resonance. [ABSTRACT FROM AUTHOR]

Reduced dimension variational calculations have been performed for the rovibrational level structure of the S1 state of acetylene. The state exhibits an unusually complicated level structure, for various reasons. First, the potential energy surface has two accessible conformers, trans and cis. The cis conformer lies about 2700 cm-1 above the trans, and the barrier to cis-trans isomerization lies about 5000 cm-1 above the trans minimum. The trans vibrations ?4 (torsion) and ?6 (asym. bend) interact very strongly by Darling-Dennison and Coriolis resonances, such that their combination levels and overtones form polyads with unexpected structures. Both conformers exhibit very large x36 cross-anharmonicity since the pathway to isomerization is a combination of ?6 and ?3 (sym. bend). Near the isomerization barrier, the vibrational levels show an even-odd K-staggering of their rotational levels as a result of quantum mechanical tunneling through the barrier. The present calculations address all of these complications, and reproduce the observed K-structures of the bending and C-C stretching levels with good qualitative accuracy. It is expected that they will assist with the assignment of the irregular patterns near the isomerization barrier. [ABSTRACT FROM AUTHOR]

A systematic analysis of the S1-trans (A1Au) state of acetylene, using IR-UV double resonance along with one-photon fluorescence excitation spectra, has allowed assignment of at least part of every single vibrational state or polyad up to a vibrational energy of 4200 cm-1. Four observed vibrational levels remain unassigned, for which no place can be found in the level structure of the trans-well. The most prominent of these lies at 46 175 cm-1. Its 13C isotope shift, exceptionally long radiative lifetime, unexpected rotational selection rules, and lack of significant Zeeman effect, combined with the fact that no other singlet electronic states are expected at this energy, indicate that it is a vibrational level of the S1-cis isomer (A1A2). Guided by ab initio calculations [J. H. Baraban, A. R. Beck, A. H. Steeves, J. F. Stanton, and R. W. Field, J. Chem. Phys. 134, 244311 (2011)] of the cis-well vibrational frequencies, the vibrational assignments of these four levels can be established from their vibrational symmetries together with the 13C isotope shift of the 46 175 cm-1 level (assigned here as cis-3161). The S1-cis zero-point level is deduced to lie near 44 900 cm-1, and the ν6 vibrational frequency of the S1-cis well is found to be roughly 565 cm-1; these values are in remarkably good agreement with the results of recent ab initio calculations. The 46 175 cm-1 vibrational level is found to have a 3.9 cm-1 staggering of its K-rotational structure as a result of quantum mechanical tunneling through the isomerization barrier. Such tunneling does not give rise to ammonia-type inversion doubling, because the cis and trans isomers are not equivalent; instead the odd-K rotational levels of a given vibrational level are systematically shifted relative to the even-K rotational levels, leading to a staggering of the K-structure. These various observations represent the first definite assignment of an isomer of acetylene that was previously thought to be unobservable, as well as the first high resolution spectroscopic results describing cis-trans isomerization. [ABSTRACT FROM AUTHOR]

Fluorescence excitation spectra and wavelength-resolved emission spectra of the C3-Kr and C3-Xe van der Waals (vdW) complexes have been recorded near the 22 -0, 22 +0, 24 -0, and 110 bands of the A1Πu-X1Σg+ system of the C3 molecule. In the excitation spectra, the spectral features of the two complexes are red-shifted relative to those of free C3 by 21.9-38.2 and 34.3-36.1 cm-1, respectively. The emission spectra from the A state of the Kr complex consist of progressions in the two C3-bending vibrations (ν2, ν4), the vdW stretching (ν3), and bending vibrations (ν6), suggesting that the equilibrium geometry in the X state is nonlinear. As in the Ar complex [Zhang et al., J. Chem. Phys. 120, 3189 (2004)], the C3-bending vibrational levels of the Kr complex shift progressively to lower energy with respect to those of free C3 as the bending quantum number increases. Their vibrational structures could be modeled as perturbed harmonic oscillators, with the dipole-induced dipole terms of the Ar and Kr complexes scaled roughly by the polarizabilities of the Ar and Kr atoms. Emission spectra of the Xe complex, excited near the A, 22- level of free C3, consist only of progressions in even quanta of the C3-bending and vdW modes, implying that the geometry in the higher vibrational levels (υbend ≥ 4, Evib ≥ 328 cm-1) of the X state is (vibrationally averaged) linear. In this structure the Xe atom bonds to one of the terminal carbons nearly along the inertial a-axis of bent C3. Our ab initio calculations of the Xe complex at the level of CCSD(T)/aug-cc-pVTZ (C) and aug-cc-pVTZ-PP (Xe) predict that its equilibrium geometry is T-shaped (as in the Ar and Kr complexes), and also support the assignment of a stable linear isomer when the amplitude of the C3 bending vibration is large (υ4 ≥ 4). [ABSTRACT FROM AUTHOR]

Rotational analyses have been carried out for the overtones of the ν4 (torsion) and ν6 (in-plane cis-bend) vibrations of the à 1Au state of C2H2. The v4+v6=2 vibrational polyad was observed in high-sensitivity one-photon laser-induced fluorescence spectra and the v4+v6=3 polyad was observed in IR-UV double resonance spectra via the ground state ν3 (Σ+u) and ν3+ν4 (Πu) vibrational levels. The structures of these polyads are dominated by the effects of vibrational angular momentum: Vibrational levels of different symmetry interact via strong a-and b-axis Coriolis coupling, while levels of the same symmetry interact via Darling–Dennison resonance, where the interaction parameter has the exceptionally large value K4466=-51.68 cm-1. The K-structures of the polyads bear almost no resemblance to the normal asymmetric top patterns, and many local avoided crossings occur between close-lying levels with nominal K-values differing by one or more units. Least squares analysis shows that the coupling parameters change only slightly with vibrational excitation, which has allowed successful predictions of the structures of the higher polyads: A number of weak bands from the v4+v6=4 and 5 polyads have been identified unambiguously. The state discovered by Scherer et al. [J. Chem. Phys. 85, 6315 (1986)], which appears to interact with the K=1 levels of the 33 vibrational state at low J, is identified as the second highest of the five K=1 members of the v4+v6=4 polyad. After allowing for the Darling–Dennison resonance, the zero-order bending structure can be represented by ω4=764.71, ω6=772.50, x44=0.19, x66=-4.23, and x46=11.39 cm-1. The parameters x46 and K4466 are both sums of contributions from the vibrational angular momentum and from the anharmonic force field. For x46 these contributions are 14.12 and -2.73 cm-1, respectively, while the corresponding values for K4466 are -28.24 and -23.44 cm-1. It is remarkable how severely the coupling of ν4 and ν6 distorts the overtone polyads, and also how in this case the effects of vibrational angular momentum outweigh those of anharmonicity in causing the distortion. [ABSTRACT FROM AUTHOR]

Rotational analyses have been carried out for the overtones of the ν4 (torsion) and ν6 (in-plane cis-bend) vibrations of the à 1Au state of C2H2. The v4+v6=2 vibrational polyad was observed in high-sensitivity one-photon laser-induced fluorescence spectra and the v4+v6=3 polyad was observed in IR-UV double resonance spectra via the ground state ν3 (Σ+u) and ν3+ν4 (Πu) vibrational levels. The structures of these polyads are dominated by the effects of vibrational angular momentum: Vibrational levels of different symmetry interact via strong a-and b-axis Coriolis coupling, while levels of the same symmetry interact via Darling–Dennison resonance, where the interaction parameter has the exceptionally large value K4466=-51.68 cm-1. The K-structures of the polyads bear almost no resemblance to the normal asymmetric top patterns, and many local avoided crossings occur between close-lying levels with nominal K-values differing by one or more units. Least squares analysis shows that the coupling parameters change only slightly with vibrational excitation, which has allowed successful predictions of the structures of the higher polyads: A number of weak bands from the v4+v6=4 and 5 polyads have been identified unambiguously. The state discovered by Scherer et al. [J. Chem. Phys. 85, 6315 (1986)], which appears to interact with the K=1 levels of the 33 vibrational state at low J, is identified as the second highest of the five K=1 members of the v4+v6=4 polyad. After allowing for the Darling–Dennison resonance, the zero-order bending structure can be represented by ω4=764.71, ω6=772.50, x44=0.19, x66=-4.23, and x46=11.39 cm-1. The parameters x46 and K4466 are both sums of contributions from the vibrational angular momentum and from the anharmonic force field. For x46 these contributions are 14.12 and -2.73 cm-1, respectively, while the corresponding values for K4466 are -28.24 and -23.44 cm-1. It is remarkable how severely the coupling of ν4 and ν6 distorts the overtone polyads, and also how in this case the effects of vibrational angular momentum outweigh those of anharmonicity in causing the distortion. [ABSTRACT FROM AUTHOR]

A number of low-N lines of the X 6Σ+←A 6Σ+(0,0) band of chromium monodeuteride, CrD, have been recorded at near the natural linewidth limit by high resolution laser excitation spectroscopy of a supersonic molecular beam sample. The shifts and splitting of these lines caused by a static electric field have been analyzed to give the permanent electric dipole moments of the X 6Σ+(υ=0) and A 6Σ+(υ=0) states as 3.510(33) and 1.153(3) D, respectively. The dipole moment of the A 6Σ+(υ=0) state can be measured with higher precision because of some interesting near degeneracies in its level structure. The trends in the observed dipole moments for the first-row transition metal monohydrides are rationalized and compared with theoretical predictions. [ABSTRACT FROM AUTHOR]

The fine and hyperfine interaction parameters in the [18.8] 3[uppercase_phi_synonym] (υ=0) and X 3[uppercase_phi_synonym] (υ=0) states of cobalt monofluoride, CoF, have been determined from an analysis of high-resolution laser induced fluorescence spectra of the [18.8] 3[uppercase_phi_synonym]3-X 3[uppercase_phi_synonym]3 and [18.8] 3[uppercase_phi_synonym]4-X 3[uppercase_phi_synonym]4 band systems. The previously reported pure rotational transitions of the X 3[uppercase_phi_synonym]4(υ=0) state [T. Okabayashi and M. Tanimoto, J. Mol. Spectrosc. 221, 149 (2003)] were included in the data set. The hyperfine parameters for 59Co (I=7/2) and 19F (I=1/2) have been interpreted using atomic data together with a proposed molecular orbital description for the [18.8]3[uppercase_phi_synonym]i and X 3[uppercase_phi_synonym]i states. A comparison of the hyperfine parameters in the X 3[uppercase_phi_synonym] state of cobalt monohydride, CoH, with those of the X 3[uppercase_phi_synonym] state of CoF reveals that the bonding in the two molecules is significantly different. It is shown that, in a situation where the Ω substates of a multiplet degenerate electronic state are analyzed separately, the Fermi contact parameter b can be determined with fair accuracy from the apparent centrifugal distortion of the hyperfine structure. [ABSTRACT FROM AUTHOR]

Rotational analyses have been carried out at high resolution for the 000-000 and 000-100 bands of the à 1Πu-X 1Σg+ transition of supersonic jet-cooled C3. Two different spectra have been recorded for each band, using time gatings of 20–150 and 800–2300 ns. At the shorter time delay the spectra show only the lines observed by many previous workers. At the longer time delay many extra lines appear, some of which have been observed previously by [McCall et al.Chem. Phys. Lett. 374, 583 (2003)] in cavity ring-down spectra of jet-cooled C3. Detailed analysis of these extra lines shows that at least two long-lived states perturb the à 1Πu, 000 state. One of these appears to be a 3Σu- vibronic state, which may possibly be a high vibrational level of the b 3Πg state, and the other appears to be a P=1 state with a low rotational constant B. Our spectra also confirm the reassignment by McCall et al. of the R(0) line of the 000-000 band, which is consistent with the spectra recorded towards a number of stars that indicate the presence of C3 in the interstellar medium. Fluorescence lifetimes have been measured for a number of upper-state rotational levels. The rotational levels of the à 1Πu state have lifetimes in the range of 230–190 ns, decreasing slightly with J; the levels of the perturbing states have much longer lifetimes, with some of them showing biexponential decays. An improved value has been obtained for the ν1 vibrational frequency of the ground state, ν1=1224.4933±0.0029 cm-1. [ABSTRACT FROM AUTHOR]

The vibrational energy levels of the jet-cooled GeCH and GeCD radicals have been studied by a combination of laser-induced fluorescence and wavelength-resolved emission techniques. The radicals were produced in a pulsed electric discharge free jet expansion using methyltrichlorogermane and tetramethylgermane-d[sub 12] precursors. A re-examination of the weaker hot bands in the LIF spectrum has provided a more complete vibrational analysis of the upper state energy levels. The single vibronic level emission spectra obtained by pumping several bands of each isotopomer were analyzed to provide information on the low-lying ground state vibronic energy levels up to 3000 cm-1 above the zero-point level. Strong interactions occur in these molecules between vibronic levels with the same value of P, but differing by one unit of v[sub 2]; such interactions were first described for NCS by Northrup and Sears [Mol. Phys. 71, 45 (1990)] and are conveniently called “Sears resonances.” The spectra of GeCH were further complicated by Fermi resonances between the bending and Ge–C stretching levels. Despite these difficulties, it proved possible to analyze the data using a standard Renner-Teller model with the addition of Sears resonance coupling terms. The validity of the fitted parameters was tested using the isotope relations. The Sears resonance parameters for GeCH are much larger than those of NCS, a result of the much stronger vibronic coupling in the germanium methylidynes. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The optical Stark effect has been measured for the &Btilde; ²Σ[sup +] - &Xmacr; ²Σ[sup +], 3[sub 0]¹, and 2[sub 0]¹(P' = 3/2) bands of lanthanum imide, LaNH, prepared in a supersonic molecular beam. The permanent electric dipole moment, μ, for the &Xtilde;²Σ[sup +] state was determined to be 2.53 ± 0.06 D from measurements of the second-order Stark shifts in the &Btilde; ²Σ[sup +] - &Xtilde;²Σ[sup +], 3[sub 0]¹ band. (ν[sub 3] is the La-N stretching vibration, of symmetry σ[sup +].) The dipole moment in the &Btilde; ²Σ[sup +] state is too small to be determined from the Stark shifts in this band, but could be determined from the first-order Stark splittings in the P' = 3/2 component of the B ²Σ[sup +], 2¹ bending fundamental (of upper state π symmetry); it was found to be 0.3 ± 0.2 D. A comparison is made with LaO and other isovalent molecules involving Group IIIA atoms. [ABSTRACT FROM AUTHOR]

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... [ABSTRACT FROM AUTHOR]

We present a complete analysis of the hyperfine structure of the MnH A 7Π–X 7Σ+ (0,0) band near 5680 Å, studied with sub-Doppler resolution by intermodulated fluorescence spectroscopy. Magnetic hyperfine interactions involving both the 55Mn (I=5/2) and 1H (I=1/2) nuclear spins are observed as well as 55Mn electric quadrupole effects. The manganese Fermi contact interaction in the X 7Σ+ state is the dominant contributor to the observed hyperfine splittings; the ΔF=0, ΔN=0, ΔJ=±1 matrix elements of this interaction mix the electron spin components of the ground state quite strongly at low N, destroying the ‘‘goodness’’ of J as a quantum number and inducing rotationally forbidden, ΔJ=±2 and ±3 transitions. The hyperfine splittings of over 50 rotational transitions covering all 7 spin components of both states were analyzed and fitted by least squares, allowing the accurate determination of 14 different hyperfine parameters. Using single electronic configurations to describe the A 7Π and X 7Σ+ states and Herman–Skillman atomic radial wave functions to represent the molecular orbitals, we calculated a priori values for the 55Mn and 1H hyperfine parameters which agree closely with experiment. We show that the five high-spin coupled Mn 3d electrons do not contribute to the manganese hyperfine structure but are responsible for the observed proton magnetic dipolar couplings. Furthermore, the results suggest that the Mn 3d electrons are not significantly involved in bonding and demonstrate that the molecular hyperfine interactions may be quantitatively understood using simple physical interpretations. [ABSTRACT FROM AUTHOR]

Sub-Doppler spectra of the A 7Π–X 7Σ+ (0,0) band of gas phase MnH near 5680 Å were recorded by intermodulated fluorescence spectroscopy. The spectra reveal hyperfine splittings arising from both the 55Mn and 1H nuclear spins. Internal hyperfine perturbations have been observed between the different spin components of the ground state at low N‘. From a preliminary analysis of several rotational lines originating from the isolated and unperturbed F1(J‘=3) spin component of the X 7Σ+(N‘=0) level, the 55Mn Fermi contact interaction in the ground state has been measured as bF=Aiso =276(1) MHz. This value is 11% smaller than the value obtained by Weltner et al. from an electron-nuclear double resonance (ENDOR) study of MnH in an argon matrix at 4 K. This unprecedented gas-to-matrix shift in the Fermi contact parameter is discussed. [ABSTRACT FROM AUTHOR]

The Stark effect of the R(2), Q(2) and P(3) lines of the Ω’=2-X 5 Δ2 subband of the ‘‘orange’’ system of iron monoxide at 5919 Å has been measured. Values for the permanent electric dipole moments μ of 4.7±0.2 and 2.6±0.2 D for the ground and excited electronic states, respectively, were derived from the analysis of the Stark shift. The results are discussed in terms of the various bonding models and compared with theoretical estimates. [ABSTRACT FROM AUTHOR]