G. Dorthe

C2 Radicals in a supersonic molecular beam. Radiative lifetime of the d 3Πg state measured by laser-induced fluorescence

The combined techniques of pulsed supersonic molecular beams and radical generation by laser vaporisation of the corresponding solid target are used to produce C2 radicals seeded in a rare gas carrier beam. Extreme rotational cooling in the expansion, together with collision-free beam conditions, are shown to be particularly well suited for actual lifetime measurements. Analysis of laser-induced fluorescence decays of C2(d3Πg) species yields the following lifetime values for the first three vibrational levels of d state: τν=O = 101.8 ± 4.2 ns, τν=1 = 96.7 ± 5.2 ns, and τν=2 104 ± 17 ns.

The dissociation energy of the SiN radical determined from a crossed molecular beam study of the Si+N2O→SiN+NO reaction

Abstract The Si( 3 P J )+N 2 O(X 1 Σ + →SiN(X 2 Σ + )+NO(X 2 Π r ) reaction is studied using pulsed, crossed, supersonic molecular The SiN(X 2 Σ + ) product is probed by laser-induced fluorescence. The reaction exhibits a translational energy threshold between 0.2 and 0.3 eV. The determination of the SiN population limit just above the threshold leads to a reaction endoergicity: 0.12⩽Δe 0 ⩽0.38 eV, which combined with D 0 (N−NO)=4.93±0.01 eV yields: 4.54⩽ D 0 (SiN)⩽4.82 eV. This value is in agreemen with a recent ab initio result from Curtiss, Raghavachari, Trucks and Pople (4.58 eV) derived from the so-called Gaussian-2 theory. The validity of the experimental approach is also discussed.

The C (3PJ) + NO(X 2Πr)→ CN (X 2Σ+) + O (3PJ) reaction dynamics studied at 0.06 and 0.23 eV relative translational energy in pulsed crossed supersonic molecular beams

Abstract The C ( 3 P J ) + NO (X 2 Π r )→CN (X 2 Σ + ) + O ( 3 P J ) reaction is studied with pulsed, crossed, supersonic, molec translational energies of 0.06 and 0.23 eV. The rovibrational distributions of the CN (X 2 Σ + ) product are determined by laser-induced fluorescence. The experimental evidence strongly suggests that the reaction proceeds via a pseudo-direct mechanism. The rovibrational distributions differ from the prior outcome. At lower collision energy, the fraction of available energy channelled into vibration and rotation is 〈ƒ V 〉 = 0.30 and 〈ƒ R 〉 = 0.15, respectively. At higher collision energy, experiments show that the additional translational energy is converted largely into CN product rotation (55%) and vibration (28%). Evidence is also found for forward scattering. The agreement with theoretical results is discussed.

Vibrational distribution in CN(A 2Πi) from the reaction C + N2O → CN + NO

Abstract Atomic carbon was produced in low-pressure H + halomethane diffusion flames using a discharge flow system. Intense chemiluminescence of CN red bands attributed to the reaction C + N 2 O → CN + NO was observed when N 2 O was added. Relative vibrational populations in the CN(A 2 Π i ) state were determined.

Kinematic Effects on Laser-induced Fluorescence Measurements Performed in Reactive Crossed Beam Experiments

A simple, realistic model is developed to take into account kinematic effects on laser-induced fluorescence (LIF) measurements in crossed beam reactive scattering experiments. The conversion factor from nascent populations to measured densities (which are proportional to the LIF intensity) is calculated for several cases of practical interest. The density-flux transformation proposed by Zare and coworkers arises from the model as a limiting case. Results concerning the C

Dynamics of the reactions of aluminium atoms studied with pulsed crossed supersonic molecular beams

The reactive collisions of aluminium atoms with O2, CO2 and SO2 have been studied with crossed pulsed supersonic molecular beams. Aluminium atoms were obtained from vaporization of an aluminium rod, using an excimer laser. They were probed, together with the product AlO, by laser-induced fluorescence. Collision energy ranges were 0.08–0.49 eV for Al + O2, 0.14–0.53 eV for Al + CO2 and 0.30–1.19 eV for Al + SO2. The variation of AlO rovibrational distributions and reactive cross-sections with collision energy has been determined for each reaction. The value D0°(AlO)= 5.26 ± 0.03 eV has been found for the AlO dissociation energy.

Origin of C2 high-pressure bands observed in the products of a microwave discharge through CO

Abstract The origin of C 2 high-pressure bands observed in discharges through CO has not been cleared up. The suggestion by Little and Browne of a collisional transfer between the metastable C 2 ( 5 Π g , v =0) and the radiative C 2 (d 3 Π g , v =6) level was progress. However, these authors claimed that only the combination reaction C+C+M→C 2 +M should be invoked for the production of the metastable level, excluding the C+C 2 O→C 2 +CO reaction that other authors believed to be at the origin of the C 2 HP bands. The correlation diagram of the C+C 2 O→C 2 +CO reaction shows that C 2 ( 5 Π g ) + CO correlates with ground-state reactants while C 2 (d 3 Π g ) + CO does not. Such a reaction could thus be involved in the C 2 HP bands. A kinetic study of these bands in a fast-flow reactor, downstream from a microwave discharge through CO diluted in He, demonstrated that both reactions C + C + M and C+C 2 O were involved. It could be concluded that the C+C 2 O→C 2 +CO reaction has a lower branching ratio for C 2 ( 5 Π g ) production than C+C+M→C 2 +M. However, the C+C 2 O reaction has in most discharges, as in ours, a greater reaction rate than that of the C+C+M reaction so its contribution is not negligible and may be the main one if the dissociation rate of CO is low.

Reactive scattering using pulsed crossed supersonic molecular beams. Example of the C+NO→CN+O and C+N2O→CN+NO reactions

The dynamics of the C+NO→CN+O and C+N2O→CN+NO reactions are reinvestigated using a pulsed supersonic crossed molecular beam apparatus. Laser vaporization of graphite at the exit of a pulsed nozzle is used to produce the atomic carbon beam. Laser induced fluorescence spectra of the CN scattered product have been obtained for both reactions.

NO(B 2Πr and A 2Σ+) chemiluminescence from the reaction C+NO2 → CO+NO at 300 K

The C+NO2→CO+NO reaction at 300 K has been shown to exhibit a strong ultraviolet chemiluminescence from NO (B 2Πr) and a weak one from NO(A 2Σ+). The NO (B 2Πr)v’=0 production rate was found to be approximately ten times greater than that of NO (A  2Σ+)v’=0. No chemiluminescence either from NO(C 2Πr) or NO (D 2Σ+), however energetically accessible, could be observed. These features are in close agreement with the Cs symmetry correction diagram for this reaction. The nascent vibrational distribution of NO(B 2Πr) was found to be much cooler than the prior statistical one.

Fast-flow study of the C+NO and C+O2 reactions

Abstract The C+NO and C+O2 reactions were studied, at room temperature, in a low-pressure fast-flow reactor. C atoms were obtained from the reaction of CBr4 or CCl4 with potassium atoms and probed by their VUV resonance fluorescence. For C+NO, the overall rate constant was determined as (5.4±0.8)×10−11 cm3 molecule−1 s−1 and for C+O2 as (2.5±0.4)×10−11 cm3 molecule s−1. For the C+NO reaction, yielding N( 2 D , 4 S )+CO and O( 3 P )+CN, the atomic products were also probed by their VUV resonance fluorescence. The [ N ( 2 D )+ N ( 4 S )]/[ O ( 3 P )] branching ratio was estimated as 1.5±0.3.