States Of Molecular Hydrogen Research Articles

Error bounds for the nonrelativistic electronic ground state energy of molecular hydrogen

Upper and lower bounds are calculated for the nonrelativistic electronic ground state energy of the1Σg+ state of molecular hydrogen using the method of variance minimization with Hylleraas-CI functions. In order to solve the occurring new integrals centered interparticle coordinates were introduced.

Collisional excitation of H2 molecules by H atoms

Three-dimensional quasi-classical trajectories on an accurate potential energy surface have been used to determine converged state-to-state rate constants for transitions among the low-energy (v, j) states of molecular hydrogen as the result of collisions with atomic hydrogen in a warm gas. Where available, fully converged three-dimensional quantum cross sections have been incorporated into the evaluation of the rate constants. The temperature dependence of the rate constants has been parameterized over the temperature range 600-10,000 K. Critical densities and rates for ortho/para interconversion for the low-energy states are given at representative temperatures. Our results are compared with previous evaluations of rate constants for H+H 2 . Reactive and nonreactive transitions are considered separately, and the relative importance of various types of transition is discussed

Trapping of Molecular Hydrogen in Porous Silicon and at Si/SiO2 Interfaces and a Possible Reinterpretation of the Pb Center

AbstractMany recent studies of the highlighted problem of visible-range photoluminescence of porous silicon (po-Si) indicate the presence of hydrogen in this material. However, its actual role is not clear with the discussed possibilities ranging from passivation of the surface defects to some form of active participation in the photoluminescence (PL) mechanism itself. At the same time, in several magnetic resonance studies of po-Si the so-called Pb center, originally identified with the <111>-directed silicon broken bond stabilized at Si/SiO2 interfaces, has been reported.Very recently the paramagnetic state of molecular hydrogen in bulk silicon has been identified. The spin-Hamiltonian parameters of the related Si-NL52 EPR spectrum appear to be identical to those of the Pb center. This observation casts severe doubts on the original interpretation of the Pb center while, on the other hand, offering new evidence of a prominent presence of hydrogen molecules both in po-Si and at the Si/SiO2 interface. In this paper the similarities of Si-NL52 and Pb centers are examined in detail, and it is argued that the centers are the same. It is concluded that many features of the Pb center which could not be explained within the broken-bond model can be understood with the interstitial hydrogen molecule model.

Branching ratios for the dissociative decay of triplet H2.

A systematic study has been performed on the singly excited {ital n}=3 triplet gerade states of molecular hydrogen using fast-neutral-beam photofragment spectroscopy. These states fluoresce to the triplet 2{ital p} states and are analyzed according to the energy released in the subsequent dissociation process. The resulting spectra are compared with theoretical results obtained by solving the coupled nuclear Schroedinger equation. Good overall agreement is reported for both the shape of the spectra and the branching ratios for fluorescence to either one of the triplet 2{ital p} states. Rotational and vibrational couplings that affect the {ital n}=3 triplet gerade complex are well described by theory.

Direct observation of strong diabatic behavior in the n = 3 3∑ +g states of molecular hydrogen

We present experimental evidence for extreme diabatic behavior of the molecular hydrogen n = 3 3⩞ + g states by studying the shape of the nuclear vibrational wavefunctions, using translational spectoscopy. Four-state nonadiabatic calculations reproduce the experimental finding. Reassignments in the h 3⩞ + g state are suggested.

High-resolution three-photon spectroscopy and multiphoton interference in molecular hydrogen.

Under favorable circumstances, a pulse-amplified cw dye laser can be used to excite three-photon resonant, four-photon transitions without significant power broadening. We have used this technique to make precise vacuum ultraviolet measurements, and to observe the cancellation of three-photon resonances due to third-harmonic generation at much lower number densities than has previously been possible. Three transitions to the B and C states of molecular hydrogen near 100 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ have been measured with an accuracy up to 0.04 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, twice that of previous measurements.

High-energy neutron inelastic scattering from adsorbed hydrogen molecules

High-energy neutron scattering to the ν=1 state of molecular hydrogen is reported for hydrogen trapped in stage II caesium graphite. Despite the electron rich environment of the intercalate the vibrational frequency is 510±10 meV, close to the free molecule value and so there is no evidence of H 2 − formation. The kinematics of the scattering of 828, 1226 and 1546 meV neutrons from both the ν=0 →ν=0 and ν=0 →ν=1 transitions has been studied. Both transitions show recoil effects which obey the scaling relationships of the impulse approximation. No “recoil shifts”, compared to other low Q studies, of the individual vibrational and phonon density of states singularities are observed when 98 meV incident neutrons are used. The relationship between the observed phonon spectrum and the “recoil shifted” excitations for higher E 0 is discussed.

Dissociation and autoionization of the lowest doubly excited state in H 2

We report one-photon dissociation from the B 1Σ u + (ν′, J′) state of molecular hydrogen into an atom in the ground state and one in the 2s state. The excited atom is detected by means ofionization with an additional photon. In particular, dissociation into the 2s state is studied since in this way population of one unique doubly excited state, Q 1 1Σ g + (2pσ u) 2, is monitored. Photoelectron energy spectra are recorded at wavelengths which are resonant with vibrational levels ν′ in the intermediate state ranging from 1 to 8. A decreasing dissociation intensity is observed with increasing vibrational quantum number ν′. To investigate the influence of rotation we excited several rotational levels in the B 1Σ u + (ν′=4) state. Strongly varying non-Franck-Condon behavior is observed as a function of the rotational quantum number.

Tunneling in the double-minimum E F 1Σ+g state of molecular hydrogen

Motivated by the observations of tunneling resonances in the rotation–vibration structures of the EF 1Σ+g double-minimum states of H2 and D2 we calculate the resonant tunneling frequencies of these states with a semiclassical formula, using accurate ab initio potential functions with appropriate adiabatic and rotational corrections. Good agreement is obtained with the corresponding two-state interaction energies which describe these tunneling resonances and which are evaluated by fitting either the experimental term values or the accurate quantum mechanical energy eigenvalues of the double-minimum oscillator.

Dipole moments and transition probabilities of the a3 Sigma g+-b 3 Sigma u+ system of molecular hydrogen.

Multiconfiguration variational calculations are carried out of the electronic wave functions of the a ${\mathrm{}}^{3}$${\ensuremath{\Sigma}}_{g}^{+}$ and b ${\mathrm{}}^{3}$${\ensuremath{\Sigma}}_{u}^{+}$ states of molecular hydrogen, and the electric dipole transition moment between them is obtained. The dipole moment is used in a calculation of the probabilities of radiative transitions from the discrete vibrational levels of the a ${\mathrm{}}^{3}$${\ensuremath{\Sigma}}_{g}^{+}$ state to the vibrational continuum of the repulsive b${\mathrm{}}^{3}$${\ensuremath{\Sigma}}_{u}^{+}$ state as functions of the wavelength of the emitted photons, and a comparison is made with measurements of the emission spectra of the v'=0 levels of ${\mathrm{H}}_{2}$ and of ${\mathrm{D}}_{2}$. The total transition probabilities and radiative lifetimes of levels v'=0--20 are presented.

Uravnenie sostoyaniya molekulyarnogo vodoroda v megabarnoi oblasti, rol' neparnykh vzaimodeistvii

Uravnenie sostoyaniya molekulyarnogo vodoroda v megabarnoi oblasti, rol' neparnykh vzaimodeistvii

The I1Πg state of hydrogen: adiabatic corrections, energy levels, L uncoupling, and electronic transition moments

Employing Kołos and Rychlewski's ab initio wave functions for the electronic I1Πg. state of molecular hydrogen (Dieke's 3dπ 3E) we calculated the diagonal corrections for nuclear motion to the electronic energies over the internuelear-distance range R = 1 – 12 au. The vibration–rotation energy levels calculated in the adiabatic approximation are compared with spectroscopic results in H2, HD, and D2 and it is concluded that the convergence error of the electronic energy in the inner well [Formula: see text] of the double-minimum potential curve is 1.0 ± 0.5 cm−1. The electronic matrix elements of angular-momentum coupling with the [Formula: see text] state and of the dipole transition moments to the (B, B′) [Formula: see text] and C1Πu states are also presented.

The E, F 1Σ+g double-minimum state of hydrogen: Two-photon excitation of inner and outer wellsa)

Low-lying vibrational levels (v=2 and 3) of the outer well of the double-minimum E, F 1Σ+g state of molecular hydrogen are experimentally observed for the first time permitting a rotational analysis. The E, F state is excited by two-photon absorption using tunable (∼195 nm) Raman-shifted radiation of a frequency-doubled dye laser. The nonlinear absorption is detected by monitoring the subsequent photoionization of the E, F state. Homogeneous perturbations are observed between the vE=1 and vF=2 levels of the inner and outer wells, respectively. The molecular parameters for these levels (derived by a deperturbation analysis) as well as those for the unperturbed vF=3 level are compared with recent ab initio calculations and small deviations are noted. The rotational intensity distribution of the E–X (0,0) band mirrors the ground state rotational population, whereas the corresponding distributions of the E–X (1,0) and (2,0) bands as well as the F-X (4,0) band do not follow this pattern. This is interpreted in terms of vibronic coupling between the inner and outer wells of the E, F state. A comparison between the experimental rotationless intensities and those calculated from ab initio ground and excited state vibrational wave functions suggests that photoionization from the outer well is more effective than from the inner well.

Solvent effects on molecular rydberg states: the B 1Σ u state of molecular hydrogen in helium

Supermolecule calculations at the SCF level are reported for the excited B 1Σ u state of the complex H 2(He) 6 for regular and randomised environments of the hydrogen molecule. Whilst marked blue-shifts are observed in the simulated matrix environment, randomisation of the surrounding helium atoms causes the transition energy to fall to a value close to that of the isolated molecule.

Decay of electronically excited singlet states of molecular hydrogen investigated by electron-photon coincidences

The decay of electronically excited H2 and D2 singlet states between 12.2 and 16 eV has been investigated by electron-photon coincidence measurements. Asymmetric structures representing a detectable exponential decay are not due to the lifetime of the initially excited states, but result from a threefold cascade decay. The lifetime of the considered n=3 gerade singlet states delivering light in the visible region is about 33 ns. The influence of predissociation is clearly observed.

Dissociative electron attachment to the metastable c3Piustate of molecular hydrogen

The H2- 2 Pi u resonance is used in an estimation of the cross section for dissociative electron attachment (DA) to the metastable c3 Pi u state of molecular hydrogen. The cross section is found to be substantially larger than that for DA to the low vibrational levels of the ground electronic state X1 Sigma g+. It appears that DA to c3 Pi u could play an important role in the production of the relatively high densities of negative ions in low-density hydrogenic plasma.

Observation of selectively excited continuous vacuum ultraviolet emission in molecular hydrogen

Vacuum ultraviolet continuous emission from selectively excited vibrational levels of the $B^{1}\ensuremath{\Sigma}_{u}^{+}$ state of molecular hydrogen into the dissociation continuum of the electronic ground state has been observed. The intensity distribution in the continuous spectra measured quantitatively proves the theory of Dalgarno, Herzberg, and Stephens. The new radiative dissociation process makes tunable vacuum ultraviolet laser action in molecular hydrogen appear feasible.

Radiative lifetimes and hyperfine constants for the 3d complex of molecular hydrogen

Accurate experimental radiative lifetimes, disalignment cross sections, hyperfine constants, and Zeeman g factors are reported for a number of rotational levels of the 3d electronic complex and the nearby doubly excited K1Σg+ state of molecular hydrogen. The 3d complex of states is not a complete basis for calculation of the above molecular properties. A theory of the Hanle effect in the presence of hyperfine structure is presented.

Erratum: The a b i n i t i o calculation of the spin–rotational coupling in the metastable c Πu (1s,2p) state of molecular hydrogen

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Quantum mechanical approach to the chemisorption of molecular hydrogen on defect magnesium oxide surfaces

Quantum mechanical theoretical calculations have been performed on the linear atomic chain \((MgOHV_{\ddot Mg} HOMg)^{2 + } \) in order to simulate the interaction of molecular hydrogen with the defects present at the surface of activated MgO. The total energy of the system, the relative energy of the various molecular orbitals, and the electronic charge distribution have been computed for various lattice parameters (dO-O = 4.0–4.8 A) as a function of the H-H (or O-H) separation. A symmetrical motion of the hydrogen nuclei with respect to the central Mg2+ vacancy was assumed. It is shown that chemisorption of hydrogen on surface O−ions sites results in the formation of pseudo-hydroxyl groups. For a small lattice parameter (4.0 A), no stable state of molecular hydrogen has been found while an increase in the lattice parameter results in a uniform increase of the calculated activation energy for the molecular hydrogen activation process. A mechanism is proposed which is not so different from that put forward for the hydrogen activation by transition metal complexes. Molecular hydrogen is found to act as an electron donor.