J. Galy

Time resolved study of the uv and near uv continuums of xenon

The spectroscopic analysis of xenon at pressures between 50 and 700 torr shows the presence of several continuums over a wavelength range of 110–700 nm. The kinetics of two of them, 173 and 210 nm, are studied. In both cases, the shape of the light pulse, reconstituted by a time‐amplitude conversion method, is defined by a difference of two exponential terms. These terms represent the formation and the decay of the molecular species. The variation of the time constants with pressure allows the reaction constants of the various processes in the kinetic scheme to be found. The continuum in the vuv is brought about by the 3Σ+u state formed by three‐body collisions: k= (8.0±0.7)10−32 cm6 s−1 and the lifetime τ=102±2 ns; in the near uv, the molecular state has a shorter lifetime τ′1=8.2±0.5 ns but is formed like the previous one by three‐body collisions: k3= (2.3±0.06)10−30 cm6 s−1. The near uv xenon emission constants ave very close to those we previously reported for argon and krypton.

Kinetic study of the VUV xenon emissions using selective multiphoton excitation

Selective excitation of xenon by multiphoton absorption of a dye laser beam gives, in the VUV, the emissions characteristic of this gas, i.e., the resonance line at 147 nm, the first continuum at 150 nm and the second continuum at 173 nm. The kinetic analysis of these emissions was carried out, using a correlation method, between 10−2 and 600 Torr. At low pressures the temporal variation of the density of the resonant 3P1 states allowed the resonance line trapping phenomenon to be demonstrated and the natural lifetime of these states to be determined (τn =4.3 ns). At high pressures the metastable 3P2 states are involved in the emission of the second continuum. The excitation spectra plotted for the blue satellite showed the creation of states in the 4f configuration. This phenomenon indicates that multiphoton ionization is not responsible for the creation of the metastable states. These states are created from a crossing of two molecular levels, one of which is bound (0+u) and responsible for the first co...

Destruction of the levels C3Πu (ν′=0, ν′=1) of nitrogen by O2,CO2, CH4, and H2O

We study the destruction of N2C3Πu(ν′=0 and ν′=1) levels in mixtures N2–O2, N2–CO2, N2–CH4, and N2–H2O at total pressures of several hundred torr. The reciprocal of the time constant for the decay of luminous impulses, measured by time‐amplitude conversion, is a linear function of the partial pressures of the two constituents; for instance, τ−1=k1+k2pN2 +kxpx for the ν′=0 level, kx=0.9×10−2 torr−1·ns−1 (O2), 1.16×10−2 (CO2), 1.88×10−2 (CH4), and 1.36×10−2 (H2O). We compare the quenching cross sections obtained from kx with the ones of the kinetic theory. We indicate, lastly, that the energy liberated by C3Πu levels during the collision can be used for the formation of free radicals.

Energy transfer kinetics of the VUV emissions for Kr--Xe mixtures

Spectroscopic study of KrXe mixtures shows large excitation energy transfers from krypton to xenon. When small quantitities of xenon are added to krypton, these processes can be seen through the fast disappearance of the continuous krypton emissions coupled with an increase in the atomic and molecular emissions of the minority gas. The excitation transfers are very efficient since the spectra of mixtures with only a few percent Xe are very similar in shape and intensity to those of pure xenon. Kinetic analysis of all the VUV emissions enabled a complete kinetic schema of the transfer phenomena to be drawn up. They are due to binary collisions from the molecular states, Kr*2(3Σu+), which are responsible for the second krypton continuum (k2=2.107 Torr−1 s−1) and from the atomic precursor states of molecular krypton (k1=7.106 Torr−1 s−1). Both processes have large cross sections. The two paths compete in the creation of resonant Xe(3P1) states, either through direct molecule–atom transfer or by atom–atom tra...

Continuous emissions of argon and krypton in the near ultraviolet

The spectroscopic and kinetic study of argon and krypton luminescence is carried out using two complementary methods. Over the range of wavelengths from 200 to 800 nm, the optical spectrum of these gases, determined by means of a single photoelectron spectrophotometer, shows the presence of atomic lines and continuums. In the case of argon, between 400 and 500 nm, a weak continuum appears. This continuum had never been observed under similar experimental conditions. The decay of the luminosity is reconstituted by means of the time‐amplitude conversion method. The decrease of light of continuums is described by a difference of exponential terms. The variation of time constants with pressure allows the kinetic scheme which describes the mechanisms of the postluminescence to be deduced. The study of the continuums has confirmed the formation of diatomic molecules of rare gases as the result of triple collisions. The kinetic scheme is as follows: Al→k1 Al′+hν1, Al+2A→k3 A 2+A, and Al2→k′1 Al2+hν0 (continuum)....

Kinetic study of the 308 and 345 nm emissions of the molecule XeCl

The light pulses of two emissions of the molecule XeCl, centered at 308 and 345 nm, both have decay time constants that behave in a very similar way with respect to variations in the partial pressures of xenon and HCl; this is explained by collisional coupling between the states B and C of XeCl which are at the origin of the two emissions. The identification of the different collision processes and the determination of the reaction rate constants particularly underline the occurrence of a three‐body collision process between XeCl (B,C), Xe, and HCl; the rate constant is kM=(5.85±2.70)×10−5 Torr−2 ns−1. Measurements were also made of the coupling constants B→C and C→B which were found to be kBC=(2.56±1.05)×10−4 Torr−1 ns−1 and kCB=(1.45±1.05)×10−4 Torr−1 ns−1. The deduced energy gap between the two states (EB−EC=119 cm−1) is in very good agreement with the values in the literature.

3-Photon Excitation of Xenon and Frequency Tripling by Non-Linear Effect

The results obtained in a xenon multiphoton excitation experiment using a pulsed dye laser are presented. At low pressures, the 3P1 resonant state of xenon is created by 3-photon resonant absorption. At higher pressures (> 20 torr), the excitation spectrum presents 2 components situated on either side of the resonance line. Spectral analysis in this region showed that they were continually originating from the molecular states A \( 1u\left( {{}^3\sum\nolimits_u^ + {} } \right)\) and B \( O_u^1\left( {{}^1\sum\nolimits_u^ + {} } \right)\) which are themselves related to the atomic 3P1 state. In the zone of negative dispersion of the medium we demonstrated the existence of a phenomenon of frequency tripling of the excitation laser beam. The light obtained in the direction of incidence is intense, the frequency can be tuned, and the band width is very narrow.

Kinetic Study of the VUV Emissions of Ar-Kr Mixtures

The far UV spectroscopic study of argon/kryptonmixtures demonstrates the very great efficiency of the Ar-Kr transfer processes. Kinetic analysis of the main molecular emissions of the two rare gases shows that the energy exchange essentially involves the molecular states of argon -the Ar2* species are destroyed on collision with krypton with an efficient cross-section of roughly 80 A2. The metastable Kr(3P2) states, which are an indirect result of the transfer, lead, through three-body heteronuclear collisions, to the formation of radiative Kr2* species which are themselves responsible for the emission of the continuum at 145 nm.

High capacity counting device for time analysis of light pulses

Abstract An inexpensive, high capacity counting device has been made for time analysis of light pulses by time-amplitude conversion. In order to allow for particularly long storage times, it has two channels with a capacity of 10 12 pulses. The result is protected from power cuts. The total recording time is measured by a quartz clock.