The EPR spectrum of the OD radical: A determination of molecular parameters for the ground state

The gas-phase EPR spectrum of the OD radical in its ground state was recorded at 8970 MHz. Transitions were observed for levels in both spin components of the X²Π state. The measurements were combined with data from the molecular beam electric resonance spectrum and from the far-infrared spectrum to determine a set of molecular parameters for OD in the v = 0 level of the ²Π state. These parameters are used in conjunction with the corresponding ones for OH to determine values for the spin-rotation constant γ and the correction to the spin-orbit coupling parameter A_D for the level v = 0. A less reliable determination is made of the values for the spin-orbit coupling parameters A_e and α_A. The set of molecular parameters is also used to calculate the frequencies and line strengths of transitions between low-lying levels in the far infrared in order to aid the identification of OD in astrophysical sources.     

Relative transition probabilities in the A-X system of OD

As in a previous study on the OH molecule, branching ratios for emission from v′ = 0, 1 and 2 of the A²Σ⁺ state of OD have been measured using frequency-doubled, tunable dye laser excitation. The six independent ratios so obtained are used to assess calculations incorporating an electronic transition moment varying linearly with internuclear distance, a form judged superior from the OH work. Calculations of the rotational dependence of the transition probabilities in OD, and comments on some recent OH investigations are included.     

The A2Σ+-X2Πi electronic band system of the OD free radical: Spectroscopic data for the 0-0 sequence,and rotational term values for A2Σ+ and X2Πi

The A²Σ⁺-X²Π_i emission system of the OD radical has been recorded at high resolution from a discharge through flowing D₂O at 0.1 torr pressure. The 0-0, 1-1, and 2-2 bands of the Δv = 0 sequence have been analyzed in detail for the first time. A table of the vacuum wavenumbers and wavelengths in air of the rotational lines of these bands is presented, together with some additional measurements for the 0–1 band. The data are used to obtain a self-consistent set of term values for v′ and v″ = 0, 1, which reproduces the observed line frequencies with an average deviation of less than 0.02 cm^?1. Earlier, lower resolution data for bands with v′ and v″ = 2, 3 are also combined with the present measurements to give approximate term values for these higher levels.     

High-resolution emission spectrum of OH in an oxyacetylene flame from 3.7 to 0.9 μm

The vibration-rotation OH spectrum emitted by an acetylene oxygen flame has been measured between 2700 and 11 000 cm^?1 with a high-resolution Fourier Spectrometer. The main interferences in the spectra are due to water vapor absorption and emission which are mixed with OH in the source. Nevertheless, line positions to high J values (more than 20 for some P branches) of the 1-0 and 2-1 bands of the Δv = 1 sequence, 2-0, 3-1, 4-2, and 5-3 of Δv = 2 and 3-0, 4-1, and 5-2 of the Δv = 3 sequence are reported. Bands of the Δv = 3 sequence are reported here for the first time. Ground-state molecular constants of OH were derived from a least-squares fit of the data, weighted according to their estimated uncertainties. Uncertainties in the new set of molecular constants are considerably improved relative to the previously available constants. Predicted positions of some unobserved bands of OH have been calculated from these new constants for the purpose of aiding stellar and atmospheric studies.     

High-resolution infrared and microwave spectroscopy of the ν4 and 2ν2 bands of 14NH3 and 15NH3

More than two thousand Stark resonances of the ν₄ and 2ν₂ band transitions of ¹⁴NH₃ and ¹⁵NH₃ were observed at Doppler-limited resolution with a CO laser. Fourier transform infrared spectroscopy on ¹⁵NH₃ is also carried out. Thirty-six new microwave transitions including seven perturbation-enhanced transitions are observed in the v₄ = 1 excited vibrational state of ¹⁴NH₃ and ¹⁵NH₃. Accuracies of all available spectroscopic data on the v₄ = 1 and the v₂ = 2 states are evaluated and analyses of the vibration-rotation spectra are performed. The Coriolis interaction between the closely lying v₄ = 1 a (antisymmetric level) and v₂ = 2 s (symmetric level) states is explicitly included in the analysis. Smaller Coriolis interactions between the v₄ = 1 a and the v₂ = 1 s states and between the v₂ = 2 s and the v₂ = v₄ = 1 a states (i.e., (v₁, v₂, v′₃, v′₄) = (0 1 0⁰ 1¹)) are also taken into consideration. The accuracy in determination of the principal molecular constants is 10^?6. The parameters thus obtained reproduce the frequencies of the vibration-rotation transitions and inversion transitions within the accuracy of 0.0024 cm^?1.     

The far-infrared laser magnetic resonance spectra of the OD radical in ground and vibrationally excited states

Laser magnetic resonance spectra of the OD radical in low-lying vibrational levels of the X²Π state have been recorded at a variety of wavelengths in the far-infrared. The spectra have been assigned to rotational and fine-structure transitions and fitted to a model Hamiltonian to determine the appropriate molecular parameters for the levels v = 0 to 3. The results are compared with those from previous studies of OD in these vibrational levels.     

Theoretical study of the spin-orbit coupling in the X2Π state of OH

The spin-orbit coupling constant, A(r), as a function of internuclear distance (r) was computed for the X²Π state of OH, using the microscopic spin-orbit Hamiltonian, extended basis sets, and extensive configuration-interaction wavefunctions. Our best theoretical results are in excellent agreement with the “experimental” A(r) functions deduced from an inversion of the observed A_v. Our calculated first-order contributions to A_v, v ≤ 10, obtained by vibrationally averaging our theoretical A(r) function using the X²Π RKR potential, differ from experiment by less than 0.12%. A minimum occurs in the A_v at v = 7 in agreement with experiment, reflecting the local minimum in A(r) near 2.8 bohr. The second-order contributions to A_v are only about 0.1% for v ≤ 10. They arise mainly from the A²Σ⁺ state for the lower vibrational levels, but each of the A²Σ⁺, B²Σ⁺, (1)²Σ^?, (1)⁴Σ^?, and (1)²Δ states contributes significantly for higher vibrational levels. Spin-orbit centrifugal distortion parameters, A_Dv and a_Dv, are reported for v ≤ 6. The theoretical A_Dv are also in excellent agreement with experiment when the “experimental” A(r) function has the same slope at the equilibrium separation as that obtained from the effective spin-rotation constants of OH, OD, and OT.     

Vibration-rotation energies of harmonic and combination levels in tetrahedral XY4 molecules: Analysis of the 2ν2 and ν2 + ν4 bands of 12CH4

The theory and the extrapolation method described in the previous paper are used to analyze the v₂ = 2 and v₂ = v₄ = 1 levels of ¹²CH₄. In addition to the well-known parameters of the ground, v₂ = 1, and v₄ = 1 states, the computation of energy levels involves only 6 new parameters for 2ν₂ and 13 for ν₂ + ν₄ up to the fourth order of approximation. These parameters have been determined from Raman and infrared data. Forty-four Raman lines observed by Berger in the region from 3060 to 3090 cm^?1 have been assigned to the 2ν₂ band. The standard deviation obtained by fitting 39 of these transitions with the 6 corresponding parameters is 0.025 cm^?1. The calculated frequencies of ν₂ + ν₄ are compared with moderate resolution ir spectra recorded in our laboratory and the recent spectra of Hunt et al. Totally polarized weak Raman lines observed by Berger in the region from 2850 to 2900 cm^?1 have been assigned to the ν₂ + ν₄ band arising through a second-order Coriolis interaction with the ν₁ band. A project of a comprehensive treatment of the energy levels of methane between 2550 and 3650 cm^?1 is discussed.     

Calculated vibrational transition probabilities of OH(X2Π)

The theoretically derived dipole moment function of OH(X²Π) obtained by Stevens Das, Wahl, Neumann, and Krauss is used to calculate the absolute intensities of the vibrational-rotational transitions of the OH Meinel bands. The calculations take full account of the spin uncoupling and vibration-rotation coupling which markedly influence the radiative transition probabilities. The effect of lambda-doubling on the vibrational transitions is analyzed and generally found to be negligible. Results are tabulated for Δv = v′ – v″ ranging from the fundamental transitions Δv = 1 to the Δv = 5 overtone, for v′ = 1–9 and J′ = 0.5 – 15.5. A comparison is made with available data, and various features of the OH spectrum are examined that are of aeronomical and experimental interest. Thermally averaged emission rates are presented for Δv = 1–5, and the validity of the rotational temperatures commonly derived from experimental intensity distributions is questioned.     

Radiative lifetimes of OH(A2Σ) and Einstein coefficients for the A-X system of OH and OD

Radiative lifetimes of individual rotational states of OH(A²Σ) were observed using a delayed coincidence technique. The values obtained were scaled to a theoretical functional form to give τ_rad(A²Σ, v = 0, N = 1, J = $\text{3}\text{2}$ = 686 ± 14 ns. Einstein A and B coefficients for the A-X system of OH and OD were computed, using numerical integrals of a transition moment of the form Re(r) = 3.75 × 10^-30 (1-0.75 r) C … m and vibrational wavefunctions obtained from numerical solutions of the radial Schrödinger equations (including centrifugal terms) for RKR potentials for the two electronic states. Matrix elements in Hund's case b were transformed to intermediate coupling for the X state to yield proper oscillator strengths for computation of the Einstein coefficients. Tables of the A and B coefficients for the 0-0 vibrational transitions are included. Extended tables are available on microfiche or microfilm from the authors.     

Laser Stark spectroscopy of silyl fluoride in the 10-μm region: Analysis of the ν2 and ν5 bands

The v₂ = 1 and v₅ = 1 states of silyl fluoride are strongly mixed by Coriolis coupling. About 1100 Stark tuned resonances were measured in these bands using ¹²CO₂ and ¹³CO₂ lasers. These data were combined with 13 new millimeterwave measurements and 900 Fourier transform infrared measurements in a suitable model. Apart from the main Coriolis coupling ζ₂₅, it was necessary to include estimates of two further Coriolis terms to obtain a satisfactory interpretation of the data. Many vibration-rotation parameters and the dipole moments are determined.     

High-resolution infrared and microwave study of 10BF2 OH and 11BF2OH: the 5, 6l, 71, 8l, 91 and 81 91 vibrationally excited states

Abstract

High-resolution (≤2.4×10^?3cm^?1) Fourier transform infrared spectra of gas-phase ¹⁰B-enriched isotopic and natural samples of BF₂OH (difluoroboric acid) were recorded in the 400–4000 cm^?1 spectral range. Starting from the results of a previous study [Collet, D., Perrin, A., Burger, H., and Flaud, J.-M., 2002, J. Molec. Spectrosc. 212, 118], which involved the v ₈ ¹⁰BF₂ out-of-plane bending) and v₉ (OH torsion) bands of ¹¹BF₂OH, it has been possible to perform the first rovibrational analysis of the v ₅ ¹⁰BF₂ bending), v ₈ , v ₉ and v ₈+v ₉ bands of’¹¹BF₂OH, and of the v ₇ (F₂BO in-plane bending), v ₅, and v ₈+v₉ bands of ¹¹BF₂OH up to very high rotational quantum numbers. In addition, microwave transitions within the 5¹, 6¹, 7¹ and 8¹ vibrational states of ¹¹BF₂OH were measured using predictions from ab initio calculations [Breidung, J., Demaison, J., D'Eu, J.-F., Margules, L., Collet, D., Mkadmi, E. B., Perrtn, A., And Thiel, W., 2004, J. Mol. S ectrosc. (in press)]. The v ₅, v ₈, v ₉ and v ₈+v ₉ bands of’ bands of ¹⁰BF₂OH and the v ₈+v ₉ band of'BF₂OH are not significantly affected by ptrturbations, and the experimental 5¹, 8¹ and 9¹ of ¹⁰BF₂OH and the 8¹9¹ energy levels of BF20H and ¹⁰BF₂OH could be reproduced using a simple Watson-type Hamiltonian. For the v ₅ and v ₇ bands of ¹¹BF₂OH, C-type Coriolis interactions coupling the 5¹ and 7¹ energy levels with those of the 7² and 6¹ dark states, respectively, were accounted for in the calculation. In addition, an updated set of rotational parameters was provided for the unperturbed 8¹ and 9¹ vibrational states of ¹¹BF₂OH using the data from our previous analysis. In all these cases, the upper state parameters derived in this work enabled the reproduction of both the infrared and microwave data to within experimental uncertainties.     

Study of the torsion-rotation Hamiltonian for symmetric tops using the millimeter wave spectrum of methyl silane

The torsion-rotation Hamiltonian for symmetric tops has been tested in methyl silane by combining recent anticrossing molecular beam measurements in the ground torsional state (v = 0) with pure rotational spectra taken for v as high as 4. The earlier microwave data set which consisted of J = 1 ← 0 and 2 ← 1 has been greatly extended by studying millimeter transitions for J = 4 ← 3, 5 ← 4, and 13 ← 12. An analysis of the 72 rotational frequencies for v ≤ 2 and the 15 anticrossing data for v = 0 yielded an excellent fit using 14 rotational, torsional, and distortion constants including the effective values for the A rotational constant and the barrier height V₃. No satisfactory fit could be obtained when the data set was extended to include measurements for (v = 3) or (v = 4). For each of these higher torsional levels, the difference between the observed frequencies and the predictions based on the best (v ≤ 2) constants can be expressed in terms of a shift δB_v in the B rotational constant, where δB_v is a smooth function of the torsional energy. This disagreement is of particular interest because it may result from the fact that the molecule passes from hindered to free rotation as v is increased from 2 to 4. The possibility of perturbation by a low-lying vibrational level is considered briefly. The information contained in the different types of spectra is discussed; the redundancy relations are treated and a Fourier expansion of the diagonal torsional matrix elements is introduced. For ¹²CH₃²⁹SiH₃, ¹²CH₃³⁰SiH₃, and ¹³CH₃²⁸SiH₃ pure rotational spectra for v = 0 were studied briefly in natural abundance. The results were combined with existing data for two deuterated symmetric rotors to obtain a structure based only on symmetric top rotational constants.     

Radial dependence of spin-orbit and Λ-doubling parameters in the X2Π ground state of hydroxyl

Experimental spin-orbit and Λ-doubling constants of OH X²Π in the vibrational range v ≤ 10 were inverted to their operator forms. The A(r) radial form derived from the spin-orbit coupling constants has been used to calculate the spin-orbit distortion parameters, A_Dv, in the range v ≤ 4. These A_Dv values have been used to separate the totally correlated γ_v and A_Dv values obtained experimentally. Radial forms of the composite lambda-doubling operators p(r) and q(r) were generated using, for the first time, the generalized inversion procedure proposed by Watson.     

Microstructured hydroxyl environments and Raman spectroscopy in selected basic transition-metal halides

Raman vibrational spectra of the selected basic (hydroxyl OH and deuteroxyl OD) transition-metal halides, geometrically frustrated material series α-, β-, γ-Cu₂(OH)₃Cl, α-Cu₂(OH)₃Br, β-Ni₂(OH)₃Cl, β-Co₂(OH)₃Cl, β-Co₂(OH)₃Br, γ-Cu₂(OD)₃Cl, and β-Co₂(OD)₃Cl are measured at room temperature and analysed to investigate the relationship between the microstructured OH environments and their respective Raman spectra. Among these selected samples, the last two are used to determine the OH stretching vibration region (3600 cm^-1—3300 cm^-1) and OH bending vibration region (1000 cm^-1—600 cm^-1) of OH systems in the spectra. Through the comparative analysis of the distances d(metal—O), d(O—halogen), and d(OH), the strong metal—O interaction and trimeric hydrogen bond (C_3v, C_s or C₁ symmetry) are found in every material, but both determine simultaneously an ultimate d(OH), and therefore an OH stretching vibration frequency. According to the approximately linear relationship between the OH stretching vibration frequency and d(OH), some unavailable d(OH) are guessed and some doubtful d(OH) are suggested to be corrected. In addition, it is demonstrated in brief that the OH bending vibration frequency is also of importance to check the more detailed crystal microstructure relating to the OH group.     

Doppler-limited dye laser excitation spectrum of the C2 Swan band (v′ − v″ = 1 − 0)

The dye laser excitation spectrum of the Swan band (v′ ? v″ = 1 ? 0) has been observed with Doppler-limited resolution. The C₂ molecule was generated by the reaction of microwave discharge products of CF₄ with CH₄. The high sensitivity of laser excitation spectroscopy has enabled us to observe not only $\text{ΔΩ}\text{= 0}$ transitions, but also $\text{ΔΩ}\text{= ± 1}$ transitions and to determine molecular constants including the spin-orbit coupling constant for both the d³Π_g and a³Π_u states. The parameters thus obtained for a³Π_u were favorably compared with those previously obtained from the Ballik-Ramsay band. The present results on the d³Π_gv = 1 state were combined with those of an earlier Fourier spectroscopic study on the Swan band (v′ ? v″ = 0 ? 0) to derive equilibrium molecular constants for the d³Π_g state. The contributions of the spin-rotation interaction and the centrifugal correction for the spin-orbit coupling to the energy levels in a ³Π state have been discussed in detail.     

Microwave fourier transform spectroscopy of pure rotational ν4 ↔ ν4 transitions and reanalysis of the ν2ν4 dyad of methane-d4

Pure rotational transitions of a spherical top in a degenerate vibrational state have been observed directly for the first time with the help of pulsed microwave Fourier transform (MWFT) spectroscopy. Twelve rotational transitions in the v₄ = 1 vibrational excited state of CD₄ have been identified. The theoretical basis for the transition moments has been developed and the line strengths of the rotational transitions have been estimated. The measured rotational transition frequencies have been included in a reanalysis of the data from a previously recorded high-resolution FTIR spectrum of the ν₂ and ν₄ bands. The v₄ = 1 state of CD₄ is strongly coupled to the v₂ = 1 state by Coriolis interaction. Thirty molecular parameters of the $\text{ν}{}_2\text{ν}{}_4$ dyad have been fitted finally from the combined microwave and infrared data. The microwave data are reproduced with a standard deviation of 42 kHz, and the infrared data with a standard deviation of 0.0002 cm^?1; in each case, this is close to the estimated experimental prescision.     

ν7 and ν9 bands of formic acid near 16 μm

The ν₇ and ν₉ fundamental bands of formic acid were studied by Fourier transform spectroscopy with a resolving power of 0.020 cm^?1. Band centers obtained are ν₇ = 626.158 cm^?1 and ν₉ = 640.722 cm^?1. It was possible to determine rotational and centrifugal distortion parameters for both vibrational states v₇ = 1 and v₉ = 1 and also the two first-order Coriolis interaction parameters along z and x axes and the second-order Coriolis parameter along z axis. The stability of rotational and distortion parameters compared to ground state values confirms that a Watson type Hamiltonian is well adapted to such a problem.     

FT-IR Study of the Interaction Between H2O,D2O,HOD, and Pyridines

Abstract

The complexes between H₂O, D₂O, HOD and pyridine have been studied in 1,2-dichloroethane by FT-IR spectrometry. Equal splittings of the stretching bands of H₂O and D₂O about their uncoupled vibrations are observed. The coupling between the asymmetric and symmetric vibrations reaches a value of zero when the band separation is greater than 500 cm^?1 for the OH vibrations and 365 cm^?1 for the OD vibrations. The v_OH stretching frequencies of the HOD ‥ complexes and the v_OD stretching frequencies of the DOH‥ complexes increase by complex formation. These features are explained by an electronic reorganization within the hydrogen bond.     

Analysis of the ν3 and ν1 infrared bands of GeH4

The high-resolution infrared spectrum of GeH₄ in the region 2020 to 2200 cm^?1 was analyzed. Most of the observed lines were assigned to transitions of the ν₃ and ν₁ bands of the five naturally occurring isotopic species. The spectrum was fitted by diagonalizing the v₃ = 1 and v₁ = 1 Hamiltonians coupled by the dominant vibration-rotation interaction term. For each isotopic species, about 100 transitions were fitted with an overall standard deviation of 0.006 cm^?1, using only 10 adjustable parameters. The five sets of parameters obtained are consistent with the expected isotope effects.