Excited States Of Molecular Hydrogen Research Articles

Non-adiabatic mass correction for excited states of molecular hydrogen: Improvement for the outer-well HH¯ 1Σg + term values.

The mass-correction function is evaluated for selected excited states of the hydrogen molecule within a single-state nonadiabatic treatment. Its qualitative features are studied at the avoided crossing of the EF with the GK state and also for the outer well of the HH¯ state. For the HH¯ state, a negative mass correction is obtained for the vibrational motion near the outer minimum, which accounts for most of the deviation between experiment and earlier theoretical work.

Doubly excited states of molecular hydrogen by scattered electron-ion coincidence measurements

Electron energy-loss spectroscopy and electron-ion coincidence techniques were used to determine the total generalized oscillator strength distribution (GOSD) of molecular hydrogen (H2) under 200 eV incident electron energy at a scattering angle of 6 degree. Ionic GOSDs were obtained for each formed ion at each energy-loss value and were determined by scattered electron-ion coincidence measurements. The total and partial ionic GOSDs of H2 were compared with the OOSDs from the experimental results of both photon and fast-electron impacts. We observed auto-ionization induced by excitation to the optically forbidden Q 1 1Σ+ g (1) state near 28 eV. Additionally, the non-ionic GOSD, defined as the difference between the total GOSD and the total ionic GOSD, was determined. From the non-ionic GOSD, neutral dissociation from excitation to the forbidden Q 1 1Σ+ g (1) state near 28 eV and the Q 2 series near 35 eV were identified.

Efficient approach to two-center exponential integrals with applications to excited states of molecular hydrogen

A general approach to evaluation of two-centre two-electron exponential integrals with arbitrary parameters is presented. The results for the Born-Oppenheimer potential for various excited states of molecular hydrogen with Ko{\l} os-Wolniewicz functions are obtained with precision exceeding previous values by about 3 orders of magnitude.

Calculation of Potential Energy Curves of Excited States of Molecular Hydrogen by Multi-Reference Configuration-interaction Method

For the excited states of a hydrogen molecule up to n = 3 active spaces, potential energy curves (PECs) are obtained for values of the internuclear distance R in the interval [0.5, 10] a.u. within an accuracy of a.u. (Hartree) compared to the accurate PECs of Kolos, Wolniewicz, and their collaborators by using the multi-reference configuration-interaction method and Kaufmann's Rydberg basis functions. It is found that the accuracy of the PECs can be further improved beyond a.u. for that R interval by including the Rydberg basis functions with angular momentum quantum numbers higher than l = 4.

Symmetry-resolved spectroscopy by detection of a metastable hydrogen atom for investigating the doubly excited states of molecular hydrogen

Symmetry-resolved spectroscopy for investigating the doubly excited states of molecular hydrogen has been newly developed, where a metastable hydrogen atom dissociating in a direction parallel and perpendicular to the electric vector of the linearly polarized incident light is detected.

Fluorescence study of doubly excited states of molecular hydrogen

Photodissociation of molecular hydrogen has been investigated by means of fluorescence spectroscopy using synchrotron radiation. Balmer-α emission from atomic hydrogen photofragments was collected in the 20–55 eV excitation energy range. Experimental data are interpreted in terms of excitation and fragmentation of neutral doubly excited states and excited ionic states with the aid of recent theoretical model calculation.

Photodissociation of doubly excited states of molecular hydrogen studied by polarization measurement of Lyman-α fluorescence

The polarization anisotropy of Lyman-α fluorescence in the photodissociation of the doubly excited states of H2 has been measured in the 27–38 eV energy range. It has been calculated taking into account the dissociation probabilities of the various molecular states involved in the process and the depolarization due to collisional effects. The agreement between experiment and theory is very good; it shows the importance of interferences and gives confidence in the analysis of the process. The fluorescence polarization anisotropy has been calculated classically in the case of a dissociation leading to H(2pπ) + H(2pσ) excited fragments.

Fluorescence lifetimes of the [formula omitted], [formula omitted], R1Π g, and [formula omitted] states of H 2

The rovibronic structures of gerade excited states of molecular hydrogen have been investigated between 117 000 cm −1 and the second dissociation limit with extreme ultraviolet visible double resonant excitation technique. Several levels have been unambiguously assigned to the v = 0 state of the 4 s and 4 d Rydberg members 4 s σ O 1 Σ g + , 4 d σ P 1 Σ g + , 4 dπ R 1Π g , and 4 dδ S 1Δ g . The fluorescence lifetimes have been measured under collision free conditions for the first time, revealing that the lifetimes for the O 1 Σ g + ( v = 0 ) state, 172.8 and 193.7 ns for J = 0 and 1, respectively, are much longer than those for the 4 d Rydberg states. The rotational dependence of the lifetimes for the EF + GK + H 1 Σ g + , I 1Π g , and J 1Δ g states is discussed in terms of the nonadiabatic coupling among the upper gerade manifolds.

Dissociation dynamics of doubly excited states of molecular hydrogen

The experimental cross sections for the various decay channels of the doubly excited states of H2 after photon absorption have been modelled as a superposition of scaled absorption profiles. Limits of the adiabatic hypothesis for the dissociation of these states were put into evidence, and some non-adiabatic mixings could be quantified. The various dissociation channels have been identified, state by state, and the various dissociation yields determined when the dipole moment was known.

(γ, 2γ) studies on doubly excited states of molecular hydrogen

The doubly differential cross sections for the emission of two Lyman-α photons in photoexcitation of H2 have been measured as a function of incident photon energy in the range of 30–44 eV with a photon–photon coincidence technique. A cross section curve that is free from ionization and thus is attributed entirely to the doubly excited states of H2 has been obtained for the first time. A simple theoretical calculation based on the reflection approximation and semiclassical treatment of the decay dynamics in the Q21Πu(1) state of H2 has reproduced well the experimental cross section curve. It has been shown that this method, the (γ, 2γ) method, is an excellent tool for investigating spectroscopy and dynamics of doubly or multiply excited molecules.

Isotope effects in the dynamics of doubly excited states of molecular hydrogen and deuterium as studied by coincident electron-energy-loss spectroscopy

The state-resolved isotope effect on the cross sections of 2p atom formation via precursor doubly excited states of and is obtained at 80 eV incident electron energy and scattering angle by means of coincident electron-energy-loss spectroscopy as well as theoretical fits based on the reflection approximation and the survival probability. It turns out that the degree of the isotope effect depends strongly on the precursor doubly excited states and hence is a significant character of them. The origin of this dependence is discussed.

Doubly excited states of molecular hydrogen as studied by coincident electron-energy-loss spectroscopy

The doubly excited states of molecular hydrogen have been studied by means of electron-energy-loss spectroscopy in coincidence with the detection of H(2p) formation at 80 eV incident energy and scattering angle. This is the first observation of doubly excited states of in electron energy-loss spectra. It is shown that a forbidden doubly excited state makes a large contribution as well as allowed states. The measured spectrum has been analysed by theoretical fits based on the reflection approximation.

Photodissociation dynamics of doubly excited Rydberg states of molecular hydrogen

We have applied photofragment ion imaging to investigate the dissociation dynamics of low-lying, doubly excited states of molecular hydrogen. A doubly excited electronic state is one in which both of the hydrogen electrons reside in excited molecular orbitals. Two-step, two-color multiphoton excitation of H2, first via 201.8 nm, two-photon excitation into the E, F 1Σ+g(vE=0, J=1) state, followed by ∼563 nm, 1+m (m=1, 2) excitation through the B″ 1Σ+u(v=0, J=0, 2), D 1Πu(v=2, J=1, 2), and B′ 1Σ+u(v=4, J=0, 2) states provides a ready means of populating several low-lying doubly excited states of H2 at increasing internuclear separations. From these doubly excited repulsive states, both dissociation and autoionization processes are possible. Because the excitation energy remains relatively constant as each intermediate state is accessed, differences in the photodissociation dynamics via each state can be ascribed directly to the effects of changing internuclear separation and electronic symmetry of the intermediate and dissociative states. H+ fragments detected from each photodissociation pathway are distinguished by their differing velocities, determined from an ion image.

Influence of electric fields on highly excited states of H2: quantum-defect-theory approach

A quantum-defect theory of the Stark effect given recently by Sakimoto (1987) is applied to study the effects of an electric field on highly excited states of molecular hydrogen. The Stark energy levels are calculated. Also investigated are field effects on photoionisation through rotational autoionisation.

Dissociation of doubly excited states of H 2 into Rydberg atoms

We report the dissociation of doubly excited states of molecular hydrogen into an excited and a ground-state atom. After three-photon excitations to various vibrational levels in the B 1Σ u + state, one- and two-photon excitations result in doubly excited states with a (2pσ u) core of both gerade and ungerade symmetry. For the first time, excitation of Q 1 states with all principal quantum numbers is observed. Dissociation of these states results in a complete Rydberg series of atomic fragments, which are photoionized. The energy of the photoelectrons is measured. The series is characterized by the lower states, which are energetically resolved up to n = 5, and the limit n → ∞ of the series.

Zero Field Level Crossing in Excited States of Molecular Hydrogen

Zero field level crossing effects have been observed in the lines emitted from the J = 1, 2, and 3 rotational levels of the [Formula: see text] state of molecular hydrogen excited in an r.f. discharge. The polarization of the R(0), R(1), and R(2) lines of the 3d1Σ → 2p1Σ(0 → 0) band as a function of magnetic field was observed to be Lorentzian, and using the Landé g factors measured by Dieke et al. yields radiative lifetimes of 2.66 × 10−8 s, 3.83 × 10−8 s, and 3.93 × 10−8 s for J = 1,2, and 3 respectively. The half-width of the level crossing curves was observed to vary linearly with pressure in the range 15 m Torr to 90 m Torr and yield collision cross sections of [Formula: see text] for all three states. The source of the discrepancy between the first and the latter two lifetimes is discussed. The lifetime of the J = 21, 3d1Π state has also been measured with less precision and yields 3.84 × 10−8 s.