Beam-gas Conditions Research Articles

Rotational alignment from the Sr( [formula omitted])+CH 2ClI chemiluminescent reaction

The rotational alignment of the product SrI( B 2 Σ + ) is obtained from Sr( 3 P J )+CH 2ClI chemiluminescence. The experiment is carried out under beam–gas conditions. Furthermore, by simulating the chemiluminescent spectrum of SrI, the electronic state branching ratio and the product vibrational state population have been roughly estimated. According to statistical theory, the branching ratio is obtained, which is in good agreement with the experimental result.

Rotational alignment from the reactions [formula omitted] and CHCl 3

The Sr( 3 P J) +CH n Cl 4− n ( n=0, 1) → SrCl ( A 2 Π 1/2, 3/2 ; B 2 Σ +) +CH n Cl 3− n reactions have been studied by measuring their chemiluminescence under beam–gas conditions. The rotational alignments of the product SrCl(B 2 Σ +) are obtained from Sr( 3 P J)+ CH n Cl 4−n(n=0, 1) chemiluminescence. In addition, the electronic state branching ratio and the product vibrational state population have been roughly estimated by simulating the chemiluminescent spectrum of SrCl.

Reaction dynamics of the [formula omitted] systems: rotational alignment, electronic state branching ratio and vibrational state population of products

The Sr( 3 P J) + RI → SrI( A 2Π 1 2 , 3 2 ; B 2Σ +) + R ( R = CH 3, CH 3 CH 2) reactions have been studied by measuring their chemiluminescence under beam-gas conditions. The rotational alignment of the product SrI was obtained. In addition, the electronic state branching ratio and the product vibrational state population have been roughly estimated by simulating the chemiluminescent spectra of SrI.

Reaction dynamics of the [formula omitted] system: chemiluminescence, energy disposal and product polarization

The Ca( 1 D 2, 3 P J) + CH 3 → CaI(A,B) + CH 3 reactions system has been studied by measuring its chemiluminescence under beam-gas conditions. Absolute values of the state-to-state reaction cross-sections were determined at low collision energy E T ⩽ 0.20 eV . In addition, the electronic branching ratio and product energy disposal have been determined for each metastable reaction. The major changed observed in the chemiluminescence when comparing the Ca( 1D 2) reaction versus that of Ca( 3 P J) is the total yield associated with the former reaction. To the best of our spectral resolution neither the electronic branching ratio e.g. CaI(A)/CaI(B) nor the internal CaI energy disposal change significantly as the metastable Ca( 1 D 2)/ Ca( 3 P J) ratio is varied. In spite of the fact that the Ca( 3 P J) reaction is less exoergic, the CaI product appears with a higher fraction of internal energy than that of Ca( 1D 2) reaction. Thus, the fraction of the total energy appearing in CaI internal energy amounts to 57.5% in the Ca( 3 P J) reaction while it is 19.3% only for the Ca( 1D 2) reaction. This difference is discussed in the light of a distinct mechanism associated with the attack of the excited Ca atom into the CI bond. No significant chemiluminescence yield was found for the energetically open CaCH ∗ 3 channels. The product chemiluminescence polarization was also measured as a function of the metastable concentration. A significant degree of polarization was found depending upon the specific electronic excitation. The analysis of the polarization emission associated to the parallel CaI(X 2Σ + ← B 2Σ +) emission led into a strong polarization of the product rotational angular momentum. The comparison of the product rotational alignment for the kinematically identical Ca( 1 D 2, 3 P J, 1 P 1) + CH 3 → CaI ∗ ( B 2Σ +) + CH 3 reaction system showed that the CaI rotational polarization diminishes in the 3 P J → 1 D 2 → 1 P 1 sequence, e.g. as the reaction exothermicity increases. In addition the degree of polarization associated with other emission bands as for example CaI(X 2Σ + ← A 2Π 1 2 ) indicates the presence of a parallel transition which was been interpreted as mixing of Hund's case (a) and (c) appropriate for this heavy CaI diatom produced with a high rotational excitation.

Reaction dynamics of the (R  CH3, C2H5 and n-C3 H7) system: chemiluminescence, photon yield, electronic branching ratio and influence of the radical group

Abstract The Ca ( 1 D 2 , 3 P J ) + RI ( R  CH 3 , C 2 H 5 , n - C 3 H 7) → CaI ( A,B ) + R reaction system has been studied by measuring its chemiluminescence under beam gas conditions. Absolute values of the reaction cross-sections were determined at low collision energy E T ≤ 0.20 eV . In addition, the electronic branching ratio, photon yield and influence of the radical size group on the reaction cross-section have been estimated. The results are discussed in the light of different reaction mechanisms involving the attacking Ca atom into the Cz.sbnd;I bond.

Reaction cross-section and product polarization in the reaction

Abstract The Ca ( 1 D 2 ) + HBr → CaBr(A,B) + H reaction has been studied by measuring its chemiluminescence at an average collision energy of ET = 0.16 eV under beam-gas conditions. Absolute values of the reaction cross-section for both chemiluminescence channels (e.g., A and B electronic states) were found to be σ A = 2.2 ± 0.9 A 2 and σ B = 0.52 ± 0.24 A 2 . In addition, the product polarization of the chemiluminescence emission was also measured, indicating a strong product rotational angular momentum alignment. The results are discussed in the light of a recent stereodynamical model for these, heavy + heavy-light, kinematically constrained reactions.

Influence of the radical size on the Ca ∗ + ROH → CaOH ∗ + R (RCH 3, C 2H 5 and C 3H 7) reaction cross section

Absolute values of the reaction cross section, σ R, for the title reaction family have been measured by chemiluminescence emission under beam-gas conditions. The σ R values diminish as the radical group R increases in size, showing an important overall steric effect. These results are discussed in the light of simple models for reaction stereodynamics.

Product polarization in the calcium(1D2) + hydrogen chloride .fwdarw. calcium monochloride(B) + hydrogen atom reaction

The Ca( 1 D 2 )+HCl→CaCl(B)+H reaction has been studied under beam-gas conditions. The product polarization of the chemiluminescence emission was measured at 0.1 eV of collision energy, indicating a strong product rotational momentum alignment. The reaction stereodynamics are discussed with the aid of a dynamical model for kinematically constrained reactions

Chemiluminescent reactions of some bromine-containing hydrocarbons with samarium under beam—gas conditions

Abstract Chemiluminescent reactions of samarium with bromine-containing hydrocarbons are reported under atomic beam—gas conditions. The chemiluminescent emission is in the visible region and is attributed to SmBr 2 emitter. The scattering and chemiluminescent cross-sections and photon yields are determined and compared with corresponding chloro analogues. The photon yields for the emitters are found to be in the order: SmBrCl > SmBr 2 > SmCl 2 . The total cross-sections are estimated from the known polarizabilities of the reactants using the Massey—Mohr expression and are compared with those observed. The fraction of the total exoergicity appearing as product electronic excitation is estimated and is found to be about 0.1%.

Chemiluminescent reactions of samarium with some chlorinated hydrocarbons

Abstract Chemiluminescent reactions of samarium with several chlorinated hydrocarbons have been investigated under atomic beam-gas conditions. The chemiluminescent emission is attributed to the SmCl 2 * emitter. The total cross-section σ, chemiluminescent cross-section σ CL and photon yields φ have been determined under single-collision conditions. It is observed that for saturated chlorocarbons the σ CL values increase as the degree of halogination increases. Planar, unsaturated molecules yield lower σ CL values than the saturated molecules. Simple RRK considerations show that the rates derived match qualitatively with experimental σ CL values and that the exoergicity of the reaction is an important factor in the reactive scattering process.

Chemiluminescence polarization measurements under supersonic beam-gas conditions

This paper develops the feasibility of extracting useful dynamical inforamtion from chemiluminescence polarization measurements carried out under beam-gas conditions rather than crossed beam conditions in order to achieve higher signal levels. It extends the previous work of Prisant et al., 1981, J. chem. Phys., 55, 2222, to include supersonic beam conditions. Classical analysis gives a simple relationship between the polarization index, R, and the product rotational alignment, <P 2(Ĵ . [Zcirc])>. The cylindrical symmetry of the beam-gas configuration allows factorization of the alignment into dynamical and kinematic factors. The kinematic factor takes into account the fluorescence depolarization which arises from the spread of relative velocity vectors about the beam axis. Its dependence on the mass and velocity of the collision partners is derived as a function of two dimensionless parameters, θ and ω, which characterize all beam-gas configurations. The results show that for much of the parameter space, the extent of depolarization is less than 10 per cent. The spread in relative velocity vectors also leads to a degradation of the collision energy resolution. A simple analytical expression is obtained for the mean collision energy and the energy resolution is also calculated as a function of the beam-gas parameters, θ and ω. The two sets of results provide a useful guide to experimentalists choosing suitable systems for study under beam-gas conditions. Measurements of the chemiluminescence polarization as a function of collision energy, obtained using a rotor accelerated beam technique, for the kinematically constrained reaction: are found to be in good accord with theory.

Measurement of product alignment in beam–gas chemiluminescent reactions

A procedure is developed for determining the product rotational alignment in the center of mass frame from polarization measurements of the chemiluminescent atom–diatom exchange reaction A+BC→AB+C under beam–gas conditions. The degree of product alignment with respect to the initial relative velocity reaches a maximum when all reagent orbital angular momentum appears as product rotational angular momentum. For beam–gas chemiluminescence, this implies a limiting degree of polarization of the product emission referenced to the beam axis about which the initial relative velocities are cylindrically symmetric. Calculations are carried out to determine this limiting chemiluminescent polarization for a wide range of beam-gas reaction conditions. Averages over initial conditions are performed by Monte Carlo sampling. These calculations show that under realistic conditions the degree of beam–beam polarization does not exceed twice that of beam–gas polarization. Product polarization is measured in the beam–gas chemiluminescent reaction Ca(1D)+HCl→CaCl(B 2Σ+)+H and found to be greater than 20%. Because of kinematic constraints, this value closely approaches the calculated limiting polarization.

Comparison of reagent translation and vibration on the dynamics of the endothermic reaction Sr+HF

The endothermic reaction Sr+HF(v=0)→SrF+H has been studied as a function of collision energy (4–14 kcal/mole) using a crossed beam geometry in which a seeded HF beam intersects a thermal Sr beam. At the same total energy this reaction is compared to the Sr+HF(v=1, J=1) reaction carried out under beam-gas conditions with a pulsed HF laser as the excitation source. In both cases the SrF products are detected by laser induced fluorescence. Using the Ba+HF→BaF+H reaction as an internal reference, the cross section of the Sr+HF(v=1) reaction is found to be 1–10 times greater than for the Sr+HF(v=0) reaction when the same total energy is supplied as reagent translation. Product internal energy distribution and total relative cross sections as a function of collision energy are also measured. Phase space calculations are able to reproduce most of these results. This agreement and other arguments suggest that the Sr+HF reaction often proceeds via multiple encounters which scramble the reagent energy modes during the course of a reactive collision.

Chemiluminescent spectra of YbF and YbCl

We have obtained the chemiluminescent spectra of YbF and YbCl from the reactions of ytterbium with fluorine and ytterbium with chlorine dioxide under beam-gas conditions and in a high-pressure (3 Torr) flow system. Much more extensive band systems are observed than hitherto reported, and a vibrational reanalysis of the ground and low-lying states is made. Although the A- X and B- X systems appear regular in YbCl, the A 2 Π 1 2 -X 2 Σ + and B- X systems in YbF exhibit extensive vibrational perturbations. The interaction between molecular states arising from the separated atoms Yb(5 d) + X( np) as well as Yb(6 p) + X( np) is believed to cause these perturbations. An unassigned red-band system is observed in emission for both YbF and YbCl, suggesting that the lowest-lying excited state is not the A state.