Andre Chapput

Excitation of N2(B 3Pig) in the nitrogen short-lived afterglow

The excitation of the N2(B 3g) state in microwave discharges ignited in flowing nitrogen and in their short-lived afterglow is investigated. Simultaneous measurements in the post-discharge on this species and the N2+(B 2u+) ion through emissions, and also on the electronic ground state of N2 by spontaneous Raman scattering, provide information of their vibrational distribution function. A spatial study has been carried out, showing a quite slow evolution of the vibrational populations along the short-lived afterglow, and in particular the first proof of a steady vibrational distribution of N2(X 1g+) from the beginning to the bulk of this ionized region. The N2(B 3g vibrational distribution is analysed by a steady-state kinetic model taking into account all the B state excitation processes, i.e. electron collisions and reactions between molecular excited states, and quenching. The reaction between the vibrationally excited N2(X 1g+) and N2(A3u+) is shown to be the pre-eminent excitation mechanism in the short-lived afterglow.

The photoreduction of zinc tetra-2,3-pyridino porphyrazine: A photochemical, electrochemical and spectroscopic study

Abstract The behavior of zinc tetra-2,3-porphyrazine (PcZnPy) has been studied by means of spectroscopy (u.v.-visible and in situ Raman diffusion), electrochemistry and photochemistry. In contrast to its phthalocyanin analog, this dye has to undergo a one-electron reduction process prior to being able to photosensitize reduction reactions. The application of this property to perform two-electron transfers is considered.

Spectre raman en phase vapeur du borazene: détermination des constantes de coriolis des espéces E

Abstract The gas phase Raman spectrum of borazene has been recorded at medium resolution. The band contours of the E degenerate species have been observed and computer simulation of them has allowed the determination of the ζ i values. This analysis has given the value of ζ 19 and ζ 20 ; ξ 18 has been calculated from the “Zeta sum rules”. The gas phase spectrum of borazene is reported for the first time and assigned.

Time and space-resolved analysis of perturbations caused by a flame propagating through, a gas mixture by C.W. Laser multichannel raman spectroscopy

Multichannel Raman spectroscopy using a continuous wave laser excitation allows measurements of temperature and compostion variatons of a gas mixture with a time resolution of 40 ms and the simultaneous probing of two or more spatial elements in the studied mixture. This technique is applied to the study of the thermal effect caused by a hydrogen-air flame propagating through a combustion chamber.

Méthode originale de détermination de la température dans une proche postdécharge d'azote

A quantitative study of spectra obtained by Raman-Stokes scattering enables the determination of the kinetic temperature of the N2(X1 Σg+) molecule in the short lived afterglow appearing downstream from a microwave discharge in flowing pure nitrogen. The obtained value agrees with the rotational temperature deduced from the emission spectra of the N2(B3 Πg)v′ = 2 species. The temperature deduced from the emissions of N2+(B2 Σu+)v′ = 0 shows a strong discrepancy with the former explained on the basis of the radiative lifetime of the species and of the time separating collisions of the molecular species.