Makoto Murata

Doubly excited states of water in the inner valence range

The cross sections for the emission of dispersed fluorescences in the ultraviolet and visible ranges by excited hydrogen atoms, OH radicals and OH+ fragment ions produced in the photoexcitation of H2O have been obtained as a function of incident photon energy in the range 17–41 eV, in which four superexcited states have been found. Two of these states around 25 and 28 eV are doubly excited states, which have been investigated in detail for the first time, and the others are single-hole one-electron superexcited states around 19 and 31 eV. It is remarkable that the doubly excited states around 28 eV give the oscillator strengths for Balmer fluorescences comparable to those given by the nearby single-hole one-electron states around 31 eV that are built on the (2a1)−1 ion core, which seems not to be amenable to the independent electron model. The state-resolved isotope effect on the oscillator strengths for Balmer-α fluorescence in H2O and D2O has been revealed. An overview of the doubly excited states of CH4, NH3 and H2O has been given in terms of the oscillator strengths for Balmer fluorescences and their energies based on the present investigation and preceding ones by Kato et al (2002 J. Phys. B: At. Mol. Opt. Phys. 35 4383 and 2003 J. Phys. B: At. Mol. Opt. Phys. 36 3541).

Doubly excited states of methane produced by photon and electron interactions

The formation and decay of doubly excited methane in photon and electron interactions have been investigated through measuring (i) the cross sections for the emission of the Lyman-α fluorescence in the photoexcitation of CH4 as a function of incident photon energy in the range 18–51 eV and (ii) the electron-energy-loss spectrum of CH4 tagged with the Lyman-α photons at 80 eV incident electron energy and 10° electron scattering angle in the range of the energy loss 20–45 eV. Five superexcited states have been found, three of which are doubly excited states with the others being singly excited states. It has been found that the electron interaction with CH4 at 80 eV incident electron energy and 10° electron scattering angle accelerates the double excitation against the single excitation as compared with the photon interaction.

Collisional deexcitation of the excited rare gas atoms in resonant states: The Watanabe-Katsuura theory revisited

The cross sections for the collisional deexcitation of neon atoms in the lowest excited 1P1 state by Ar, Kr, Xe, N2, O2, CO, NO, and CH4, and in the lowest excited 3P1 state by O2 and CH4 have been measured at a mean collisional energy corresponding to room temperature. Data are also included for collisions of argon atoms in the lowest excited 1P1 and 3P1 states by C2H4, cyclo-C3H6, and C3H8, and collisions of krypton atoms in the lowest excited 1P1 and 3P1 states by C2H4 and cyclo-C3H6. The measured cross sections, together with those obtained in our previous studies, are compared with the cross sections calculated using the Watanabe–Katsuura theory. An extension of the Watanabe–Katsuura theory to the deexcitation of excited rare gas atoms in collisions with molecular quenchers, not atoms, is examined.

Multiply excited states of molecular nitrogen in the vacuum ultraviolet range as studied by (γ, 2γ) method

The cross sections for the emission of two photons of N fluorescence in photoexcitation of N2, differential with respect to each solid angle for the two photons, have been measured as a function of incident photon energy in the range of 28–49 eV to investigate the multiply excited states of N2. The resonance peaks attributed to the neutral excited states of N2 have been found at 36, 39, 40–44 and 45 eV in the ionization-free fluorescence cross section curve. It has turned out that these neutral excited states are multiply excited states of N2. It is remarkable that the multiply excited state of N2 at 45 eV embedded in the double ionization continuum makes a contribution comparable to those below the double ionization potential in the ionization-free cross section curve.

(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.

Inner-valence excited and multiply excited states of molecular oxygen around the double-ionization potential as probed by a pair of fluorescence photons

The cross sections for the generation of a pair of fluorescence photons in the photoexcitation of O2 differential with respect to solid angles for the emission of the photon pair have been measured as a function of incident photon energy in the range 23?47 eV using the photon?photon coincidence method, the (?, 2?) method, to investigate the inner-valence excited states and multiply excited states of O2 as superexcited states. Four superexcited states of O2 with the 3??u or 3?u symmetry have been newly found around 29, 36, 38 and 44 eV in the measured cross section curve free from ionization. It turns out that they are inner-valence excited states and multiply excited states. Two remarkable points are shown: (1) there exist superexcited states of O2 dissociating into neutral fragments even in the energy range above the double-ionization potential of O2 at 36.13 eV and (2) the values of the doubly differential cross sections decrease to a large extent around the double-ionization potential with increasing incident photon energy, both of which have been compared with the results of N2 by our previous (?, 2?) experiment. The origin of (2) is discussed in detail.