H. Hou

Reaction geometry from orbital alignment dependence of ion pair production in crossed‐beam Ba(1P1)–Br2 reactions

Strong orbital alignment dependence was observed for Ba+ produced in crossed‐beam reaction of Ba(1P1) with Br2. The peak of this dependence varied strongly with scattering angle for alignment of the p orbital in the scattering plane, with the maximum flux seen for perpendicular alignment with respect to the relative velocity vector. The measured Ba+ was always favored by alignment of the orbital in the scattering plane, regardless of laboratory scattering angle. The experimental results suggest that this charge‐transfer process is dominated by large impact‐parameter collisions which achieve collinear nuclear geometry and Σ orbital alignment at the crossing point. Orbital locking is probably not important owing to the large internuclear distance of the crossing region.

Reaction dynamics from orbital alignment dependence and angular distributions of ions produced in collision of Ba(1P) with NO2 and O3

Angular distributions, orbital alignment dependence, and energy dependence of the relative cross sections of various ions produced in crossed beams collisions of electronically excited barium with O3 and NO2 were used to explore the dynamics of these reactions. The Ba+ product from both reactions showed strong dependence on alignment of the Ba(1P) p orbital with respect to the relative velocity vector. The Ba+ was generally forward or forward‐sideways scattered, with the latter favored by the dominant perpendicular orbital alignment. Similar results for Ba+ from both O3 and NO2 suggest that electron transfer is favored for large impact parameter collisions in which the Ba p orbital is directed toward the molecule at the critical configuration, regardless of the symmetry of the available orbital in the isolated molecule. BaO+2 from the O3 reaction exhibited angular distributions and energy dependences which were reminiscent of the Ba+, albeit 2 orders of magnitude lower in intensity, indicating a close rel...

The Reactions of Na2 with O2

The reactions of Na2 with O2 were studied in a crossed-beam experiment at collision energies (Ec) of 8 and 23 kcal/mol. The formation of NaO2 + Na was observed at both collision energies, with the angular distributions of NaO2 in the center of mass coordinates peaking strongly forward with respect to the direction of the O2 beam, suggesting that the reaction is completed in a time scale that is shorter than one rotational period of the molecular system. From the velocity distribution of the products, we found that the newly formed NaO2 molecules are internally excited, with less than 20% of the available energy appearing in the translational motion of the separating products. These results indicate a “spectator stripping” mechanism, with the O2 stripping one Na off the Na2 molecule. At Ec = 23 kcal/mol, the cross section for this reaction channel, σNaO2, is estimated to be 0.8 A2. Another reaction channel which produces NaO + NaO was seen at Ec = 23 kcal/mol. The angular distribution for NaO is broad and forward-backward symmetric in the center-of-mass frame. A substantial fraction of the available energy is released into the relative motion of the products. This reaction is likely to proceed on an excited potential energy surface since a charge transfer to the excited O2 − orbitals seems necessary for breaking the O-O bond. The measurement yields a bond energy of 60 kcal/mol for the Na-O molecule, and a total cross section for this reaction channel at Ec = 23 kcal/mol, σNaO = 2 A2.

The reactions of Na{sub 2} with O{sub 2}

The reactions of Na{sub 2} with O{sub 2} were studied in a crossed-beam experiment at collision energies (E{sub c}) of 8 and 23 kcal/mol. The formation of NaO{sub 2} + Na was observed at both collision energies, with the angular distributions of NaO{sub 2} in the center of mass coordinates peaking strongly forward with respect to the direction of the O{sub 2} beam, suggesting that the reaction is completed in a time scale that is shorter than one rotational period of the molecular system. From the velocity distribution of the products, the authors found that the newly formed NaO{sub 2} molecules are internally excited, with less than 20% of the available energy appearing in the translational motion of the separating products. These results indicate a ``spectator stripping`` mechanism for the reaction, with the O{sub 2} stripping one Na off the Na{sub 2} molecules. At E{sub c} = 23 kcal/mol the cross section for this reaction channel is estimated to be 0.8 {angstrom}{sup 2}. Another reaction channel which produces NaO + NaO was seen at E{sub c} = 23 kcal/mol. The angular distribution for NaO is broad and forward-backward symmetric in the center of mass frame. A substantial fraction of the available energy is released into the relative motion of the products. This reaction is likely to proceed on an excited potential energy surface since a charge transfer to the excited O{sub 2}{sup {minus}} orbitals seems necessary for breaking the O-O bond. The measurement yields a bond energy of 60 kcal/mol for the Na-O molecule, and a total cross section of 2 {angstrom}{sup 2} for this reaction channel at E{sub c} = 23 kcal/mol.