Reactive Scattering from Brute Force Oriented Asymmetric Top Molecules:  K + C₆H₅I → KI + C₆H₅

Abstract

In a crossed molecular beam experiment, we have measured angular and time-of-flight (TOF) distributions of products formed in the reaction K + C 6 H 5 I f KI + C 6 H 5 at a collision energy of E tr ) 1.9 eV. From these data we have extracted the double-differential reaction cross section in the center-of-mass frame. The brute force technique has been applied to orient for the first time an asymmetric top, namely the reagent molecule C 6 H 5 I. The effect of molecular orientation on the angular distribution of products has been investigated. We determined the difference of product intensity for (a) preferred encounters with the I end and the phenyl end (parallel steric effect) and (b) side-on attacks with the axis pointing in two opposite directions (perpendicular steric effect). We find (i) preferred sideways scattering of KI with a mean recoil energy of 31.6% of the totally available energy; (ii) an additional reaction channel with a branching ratio of 0.65% by which a flux of slow products, most likely KI, is formed; (iii) the transformation of the data to a more adapted coordinate frame reveals that backward rather than sideways scattering reflects the dynamics of the reaction; (iv) a tight correlation between the direction of the product flux and the orientation of the molecular axis; (v) the experimental results can be rationalized by the direct interaction with product repulsion (DIPR) model; (vi) the ratio of product yield for attacks of the K atoms to the I end (head) and the phenyl end (tail) amounts to ≈28:1; (vii) the full apex angle of the cone-of-acceptance amounts to ≈110°; (viii) the harpooning mechanism and simple molecular orbital arguments rationalize the impulsive reaction mechanism implicit to the DIPR model and offer an explanation for the existence of a channel for slow KI products.

Electrostatic Hexapole State-Selection of the Asymmetric-Top Molecule Propylene Oxide

“…In the case where orientation after focusing may be difficult, 52,53 "brute force" may be required. [54][55][56][57] The enantiomeric selected forms can be used for investigations of chirality effects. The technique is considered for use at synchrotron radiation and surface science facilities for photochemistry and stereodynamics experiments.…”

Hexapole state-selection and orientation of asymmetric top molecules: CH2F2

“…The latter capability makes asymmetric tops ideal for probing stereoselective chemical effects. [1][2][3][4][5][6][7][8]30,31,33,34 A competing method for orienting asymmetric tops is the so-called ''brute force'' technique. 33,47 Molecules from a supersonically cooled expansion are passed directly through a pair of high field Stark plates without any hexapole selection.…”

“…31 Bulthuis et al have developed the theory for asymmetric top brute force orientation, 32 and Loesch and Möller have used brute force oriented C 6 H 5 I in reactive scattering studies of KϩC 6 H 5 I. 33,34 Relative to other types of molecules, asymmetric top focusing experiments are rare and none have involved more than simply measuring focusing spectra. In only two cases were the focusing spectra simulated theoretically, and in both of these the theory was simplified by approximations, the validity of which we now explore.…”

Strand spaces and rank functions:more than distant cousins

“…However much greater values of have been achieved in a number of other recent experiments. For example, ϭ24.2 was obtained for the near prolate molecule C 6 H 5 I in a 20 kV/cm electric field, 7 and ϭ38 was achieved in a 57 kV/cm field for the near oblate molecule pyridazine. 8 Fields of up to 100 kV/cm have been reported in orientation experiments.…”

“…[1][2][3][4][5][6][7][8][9] This method, known as the brute force technique, was initially applied to linear and diatomic molecules and then extended to symmetric and asymmetric polar molecules. A molecule in a moderately strong electric field exhibits two different regimes: pendular motion about oriented states at low energies and almost free rotational motion at high energies.…”