Electronic States Of OH Research Articles

Accurate ab initio potential energy curves and spectroscopic properties of the low-lying electronic states of OH− and SH− molecular anions

ABSTRACTMultireference configuration interaction method was used in order to generate accurate potential energy curves of the OH, SH, OH− and SH− electronic states correlating to the three lowest dissociation limits. These curves were used in addition with core–valence correlation and scalar relativistic corrections for the calculations of accurate spectroscopic constants of bound states, which generally are found in excellent agreement with best available experimental and theoretical values in the literature. The spin–orbit interactions between electronic states have been calculated for the cases in which the couplings were assumed to be responsible for perturbations and used to explain the predissociation of A2Σ+ state of OH and SH by dissociative states 14Σ−, 12Σ− and 1 4Π. Dipole moment functions were also computed along internuclear distances and used to explain polarity of these molecules in different calculated electronic states. In addition, stability and metastability of electronic states (X 1Σ+, A1Π and a3Π) of OH− and SH− molecular anions have been studied relatively to curves of neutral parent electronic states. Finally, we have computed adiabatic electron affinity of OH and SH and these values have been found in very good agreement with the best experimental values and resort as among the best achieved values.

Ab Initio Potential Energy Curves for the Ground and Low-Lying Excited States of OH and OH– and a Study of Rotational Fine Structure in Photodetachment

Complete basis set extrapolated ab initio potential energy curves obtained from multireference configuration interaction (MRCI) level calculations for the ground state (X(1)Σ(+)) of OH(-), and the ground state (X(2)Π) and the first excited state (A(2)Σ(+)) of OH are reported. The potential energy curves for the excited states A(1)Π, a(3)Π, and b(3)Π of OH(-) have been computed using the V6Z basis set at the MRCI level. Λ-doubling parameters p and q were calculated for the ground and the first excited vibrational states of the ground electronic state of OH using second-order perturbation theory. Using the computed potential energy curves and the rovibrational spectra for photodetachment including the fine splitting, the threshold for electron detachment has been computed. The result is in agreement with the experimental results of Goldfarb et al. [J. Chem. Phys. 1985, 83, 4364].

An ab initio quasi-diabatic potential energy matrix for OH(2Σ) + H2

A diabatic potential energy matrix for three electronic states of OH(3) has been constructed by interpolation of multi-reference configuration interaction electronic structure data. The reactive, exchange and non-reactive quenching dynamics are investigated using surface hopping classical trajectories. Classical trajectory simulations show good agreement with cross molecular beam data for the OH((2)Σ) + D(2) → HOD + D reaction.

Photodissociation Dynamics of 2-Nitropropane and 2-Methyl-2-nitropropane at 248 and 193 nm

Dynamics of formation of electronically excited NO2 and formation of OH fragment, during photo dissociation of 2-nitropropane (NP) and 2-methyl-2-nitropropane (MNP), were investigated at 193 and 248 nm. The radiative lifetime of the electronically excited NO2 fragment, observed at 193 nm, was measured to be 1.2 ( 0.1 micros and the rate coefficient of quenching of its emission by MNP was measured as (2.7 ( 0.1) x 10(-10) molecule(-1) cm3 s(-1). Formation of the ground electronic state of OH was confirmed in both molecules. State selective laser induced fluorescence technique was used to detect the nascent OH (X 2Pi, v'', J'') fragments in different ro-vibrational states, and to obtain information on energy partitioning. Though MNP and NP differ in the types of the available H atoms, the dynamics of OH formation is found to be the same in both. The relative population in different rotational states does not follow Boltzmann equilibrium distribution in both the molecules at 193 and 248 nm. The translational energies of the OH fragments, calculated from the Doppler width, are 21.2 ( 7.2 and 25.0 ( 2.5 kcal mol-1 for NP at 248 and 193 nm, respectively. The translational energies of the OH fragments, in the case of MNP, are found to be lower, 17.5 ( 4.1 and 22.0 ( 3.2 kcal mol-1,respectively, at 248 nm 193 nm. These results are compared with the earlier reports on photodissociation of nitromethane (NM), nitroethane (NE), and other nitroalkanes. All possible dissociation pathways of these molecules--NM, NE, NP, and MNPs leading to the formation of the OH fragment were investigated computationally, with geometry optimization at the B3LYP/6-311+G(d,p) level and energy calculation at the MP4(SDQ)/6-311+G (d,p) level. The results suggest that in NM, OH is formed after isomerization to CH2N(OH)O, whereas in all other cases OH is formed from HONO, a primary product of molecular elimination of nitroalkanes, formed with sufficient internal energy.

Time-domain investigation of OH ground-state energy transfer using picosecond two-color polarization spectroscopy

Two-color polarization spectroscopy was used to investigate rotational energy transfer (RET) and relaxation of orientation and alignment in the ground electronic state of OH in an atmospheric-pressure methane–air flame. Two independently tunable lasers produced nearly transform-limited infrared and ultraviolet pulses of 50 ps duration. The infrared laser excited rovibrational transitions, and delayed ultraviolet pulses probed electronic transitions from either the directly pumped or collisionally populated states. Alignment and orientation relaxation times were measured for individual rotational levels in OH X 2 Π 3/2(v=1) , and the feasibility of time-domain investigation of state-to-state energy transfer processes was demonstrated.

Studies on dissociation energies of diatomic molecules using vibrational spectroscopic constants

New analytical expression and numerical approach are suggested to calculate dissociation energies D e of diatomic molecular states using an extreme value method (EVM). Studies on some electronic states of OH, BH, N 2 , Br 2 , ClF and CO molecules show that the accuracy of the EVM dissociation energies depends on the number of correct vibrational constants used in the calculations. The convergence qualities of D e are suggested to be an alternative physical criterion to measure the qualities of the various sets of vibrational constants from different literature for the same diatomic state.

Infrared spectroscopy of OHH 2 entrance channel complexes

The rotationally-resolved infrared spectrum of the ground electronic state of OHH 2 has been observed near the OH gn = 2 ← 0 origin by an infrared-ultraviolet fluorescence depletion technique. The experimental spectrum agrees remarkably well with a fully ab initio infrared spectrum originating from the lowest intermolecular level of ortho-H 2OH. The lack of measurable homogeneous line broadening in the spectrum indicates that neither vibrational predissociation nor chemical reaction is occurring faster than 45 ps. The magnitudes of the depletions, however, suggest that these processes are taking place on the nanosecond time scale.

Refinement of the OH A 2Σ+(v=0)+Ar intermolecular potential energy surface

Several intermolecular vibrational levels of the excited electronic state of OH–Ar correlating with OH A 2Σ+(v=0)+Ar have been characterized by laser-induced fluorescence and hole-burning experiments. The OH–Ar levels identified include the lowest intermolecular level, an intermolecular bending level with a lower degree of stretching excitation than previously observed, and intermolecular levels with two quanta of bending excitation. The intensities of electronic transitions to these levels from the lowest intermolecular level of the ground electronic state of OH–Ar (X 2Π) are significantly weaker than those of transitions previously reported. These data are used to refine a semiempirical potential for OH A 2Σ+(v=0)+Ar proposed by Bowman et al. [J. Phys. Chem. 94, 2226 (1990)]. The potential parameters have been adjusted to increase the potential anisotropy and the steepness of the radial potential in the O–H–Ar well region. The bound states supported by the adjusted potential have been calculated by taking into account the electron spin angular momentum of the OH radical. The calculated vibrational energies and rotor constants reproduce the rovibrational structure observed experimentally. A theoretical simulation of the OH–Ar electronic excitation spectrum based on the adjusted intermolecular potential yields an intensity pattern which is consistent with experimental results.

Ab initio studies of molecular anions stabilized in point-charge lattices: Excited electronic states of OH −

Potential curves and spectroscopic constants for the ground and low-lying excited electronic states of OH and OH − are computed at the MCSCF level, in vacuo and in fcc point-charge lattices. Vibrationally bound 1Π and 3Π states are found 3-4 eV above the ground state of the anion and are probably responsible for the known UV luminescence spectrum of OH − in alkali halides. The excited states display OH − character, and their properties depend strongly on orientation in the lattice.

Optogalvanic OH (A ← X) spectrum

A pulsed, tunable dye-laser initiates an optogalvanic spectrum of OH between 3074 and 3098Å. The OH is in a hollow cathode discharge that originates from a mixture of Ne and ⩽0.6% H 2O. Data analysis indicates that the ground ( X) electronic state of OH has a rotational temperature of ≈250–300 K. This method appears to be a good diagnostic for the X state in discharges.

Solid propellant combustion zone structure from analysis of hydroxylradical chemiluminescence

Hydroxyl radical Chemiluminescence spectra have been obtained in the combustion zone above ammonium perchlorate composite solid propellant burning at multiatmospheric pressures in a laboratory scale strand burner. These semiresolved (.13 nm) spectra were analyzed by constructing OH synthetic spectra and employing a best-fit technique to determine the rotational temperature and vibrational population distribution in the A!, electronic state of OH in the flame. Values for rotational temperature and vibrational population distribution were obtained for pressures from 0.2 to 7.0 MPa at three positions above the propellant surface. Quantitative comparison of results over a range of pressures for a given spatial position is mitigated by the potentially significant effects of self absorption on the measured spectra. Comparisons at a given pressure for various positions above the propellant surface should not be affected by self-absorption, and show a fairly constant rotational temperature and vibrational population distribution from near the surface out to the maximum position investigated (12 mm). These results indicate that a chemical combustion environment involving short lived radical species exists at distances very far from the propellant surface even at elevated pressures. Interpretation of the spectral characteristics of the emission data also indicates highly nonequilibrium vibrational populations and possible non-Boltzmann rotational distributions which increasingly diverge from equilibrated distributions with increasing pressure.

The pure rotation spectrum of OH and the solar oxygen abundance

view Abstract Citations (71) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The pure rotation spectrum of OH and the solar oxygen abundance Sauval, A. J. ; Grevesse, N. ; Zander, R. ; Brault, J. W. ; Stokes, G. M. Abstract High-resolution low-noise spectroscopic observations of the sun obtained in the 10.6-13-micron range using the Fourier-transform spectrometer at Kitt Peak National Observatory are reported. About 100 pure rotation lines of the X 2Pi electronic state of OH with v = 0, 1, 2, and 3 are identified and characterized. The data are presented in tables and graphs and used to calculate the solar O abundance as 8.91 + or - 0.01 (in agreement with Lambert, 1978). Agreement is also found with the electric-dipole-moment function of Werner et al. (1983) and the photospheric model of Holweger and Mueller (1974). Publication: The Astrophysical Journal Pub Date: July 1984 DOI: 10.1086/162206 Bibcode: 1984ApJ...282..330S Keywords: Abundance; Hydroxyl Emission; Infrared Spectra; Rotational Spectra; Solar Spectra; Stellar Composition; Electric Dipoles; Molecular Spectra; Oxygen Spectra; Solar Atmosphere; Solar Physics full text sources ADS |

Semiempirical valence bond potential energy surfaces for simple chemical reactions:1A′ states of H2O and H2F+

A semiemprical valence bond method is employed to study the potential energy surfaces (PESs) of the lowest 1 A′ states of H2O and isoelectronic H2F+. The calculation is based on the search for the electronic configurations which play the most important rôle in the formation of the stable electronic states of the molecules and the relevant diatomic fragments. Several approximations are used to reduce the number of permutations in the calculation of the energy matrix. The Moffit atoms-in-molecule approximation is used to correct for the atomic errors arising from the poor basis set. The computed data for the lowest electronic states of OH, HF, HF+, H2O and H2F+, as well as the general behaviour of the PESs for different molecular geometries, are in good agreement with the available ab initio and experimental data.

PNO-CI and CEPA studies of electron correlation effects

Ab initio calculations of the potential curves of low laying electronic states of OH are performed on the basis of a variational configuration interaction wavefunction (PNO-CI) and the coupled electron pair approximation (CEPA).

Production of vibrationally excited OH in chemiluminescent ozone-olefin reactions

The vibration-rotation bands (Meinel bands) of the ground electronic state of OH have been observed in the chemiluminescent gas phase reactions of ozone with ethylene, propylene, 1-butene, cis-2-butene and tetramethylethylene at total pressures of about 3 torr at room temperature. The emitting species in the reactions of the 1-olefins with ozone have been tentatively identified as HCHO( 1A 2) and electronically excited α-dicarbonyl compounds.

Experimental Proof for the Existence of Nonthermal Rotational Distributions of OH (2Σ+) in Flames

Experiments have been carried out to determine whether nonthermal rotational distributions in the 2Σ+ electronic state of OH observed in certain flames are caused by self-absorption. A study of emission (single and double path) and absorption by OH between 3064 A and 3350 A in atmospheric and low-pressure flames has shown that self-absorption is negligible in at least two cases in which nonthermal distributions are found. This leads to the conclusion that anomalous ``temperatures'' of OH measured previously in hydrocarbon flames at low pressure and in highly diluted flames at atmospheric pressure are real.