Chemiluminescence polarization measurements under supersonic beam-gas conditions

Abstract

This paper develops the feasibility of extracting useful dynamical information 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~(J' . ~)). 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, p and ~, which characterize all beam-gas configurations. The results show that for much of the parameter space, the extent of depolarization is less than I0 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, p and ~. 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 :Xe*(~P~,0) + HCI -+XeCI* + H -~Xe + C1 + H + h v are found to be in good accord with theory.

Deuterium Isotope Effect on the Atomic Orbital Alignment Dependence in the Reaction of the Oriented Ar (3P2) with CH3CN (CD3CN)

“…[12][13][14][15][16] Because this type of reaction is likely to be initiated by the electron exchange mechanism, the effects of molecular orientation in such processes have been observed in our laboratory. [17][18][19][20] The reaction of Ar ( 3 P 2 ) + CH 3 CN (CD 3 CN) is one of the widely studied reaction systems so far.…”

Reactions of Xe(3 P 2) and Xe(3 P 1) with HCl, HBr and HI; energy utilization, energy disposal, product rotational polarization and reaction dynamics

“…Crossed beam and beam gas arrangements are employed to gain dynamical information from measurements of the differential and integral cross-sections for inelastic and reactive scattering and from the collisional energy dependence of the product rotational alignment obtained from the chemiluminescence polarization. The light mass of the departing H atom places a strong kinematic constraint on the reaction dynamics but some of the dynamical features are expected to be exposed at collision energies near threshold where the contour of the potential energy surface becomes an important parameter [3,14,15]. This is true for the polarization measurements which are shown to be particularly sensitive to the nature of the potential energy surface even in these highly constrained reactions.…”

“…(a) Rittner potentials for bound upper states Reactions of Xe(3p2) and Xe(aP1) 259 relative velocity vectors when beam-gas conditions are employed, have been presented elsewhere [14,15]. The experimental conditions maintained in the beamgas experiments are summarized in table 1.…”

“…The data were corrected for the spread in relative velocity vectors using methods described previously [14,15] ............... ~.~ ..... -...~.:~.!…”

Dynamical and stereodynamical studies of alkaline-earth atom–molecule reactions

“…The azimuthal average addition (AAA) theorem [90] is used to correct the beam-gas blurring effect of the rotational alignment given by hP 2 ð j 0 Á zÞi, e.g.…”