Piergiorgio Casavecchia

Reactive scattering of O(1D) + H2

The angular and velocity distribution of OH product frorn the O(1 D) + H2 reaction at 2.7 kcalmole collision energy has been obtained in a crossed molecular beam study. The product is found to be forward-backward symmetric; most of the reaction occurs through insertion of the oxygen to form ground electronic state H2O.

Exploring the reaction dynamics of nitrogen atoms: A combined crossed beam and theoretical study of N(2D)+D2→ND+D

In the first successful reactive scattering study of nitrogen atoms, the angular and velocity distribution of the ND product from the reaction N(2D)+D2 at 5.1 and 3.8 kcal/mol collision energies has been obtained in a crossed molecular beam study with mass spectrometric detection. The center-of-mass product angular distribution is found to be nearly backward–forward symmetric, reflecting an insertion dynamics. About 30% of the total available energy goes into product translation. The experimental results were compared with those of quasiclassical trajectory calculations on an accurate potential energy surface obtained from large scale ab initio electronic structure computations. Good agreement was found between the experimental results and the theoretical predictions.

Coupled‐channel study of halogen (2P) + rare gas (1S) scattering

Quantum mechanical coupled‐channel (CC) scattering calculations are reported using realistic adiabatic potentials for the 2P+1S interaction of F–Ar, F–Xe, and Cl–Xe. Differential cross sections dσ/dω derived from a simple elastic approximation appropriate for large spin orbit interactions accurately reproduce all the gross features computed by the coupled‐channel method. This finding supports the extraction of interaction potentials from laboratory differential cross sections I (ϑ) via an elastic analysis. Integral inter and intramultiplet changing cross sections are expressed conveniently in terms of Grawert’s B(j, j’;g) coefficient. Information on the collision dynamics is extracted by following the partial wave dependence of selected B(j, j’;g). Classical turning point analysis, based on the values of the large l‐waves for which these partial wave contributions Bl(j, j’;g) begin to rise above zero, leads to the conclusion that both intermultiplet and first order forbidden intramultiplet transitions are...

Rare gas–halogen atom interaction potentials from crossed molecular beams experiments: I(2P3/2)+Kr, Xe(1S0)

Angular distributions of I(2P3/2) scattered off Kr and Xe(1S0) in the thermal energy range have been measured in crossed molecular beams experiments. The interaction potentials for two relevant states (Xu20091/2u2009andu2009Iu20093/2) for each of the systems are obtained by using an approximate elastic scattering analysis, which neglects nonadiabatic coupling, as previously done for other rare gas–halogen systems. The I–Xeu2009 (Xu20091/2) potential (e = 0.69u2009kcal/mol, rm = 4.30u2009A) and, to some extent, I–Kru2009(Xu20091/2) potential (e = 0.55u2009kcal/mol, rm = 4.05u2009A) shows a slightly more attractive interaction than the interaction potentials of Xe–Xe and Xe–Kr, but the I–Xeu2009(Iu20093/2) potential (e = 0.48u2009kcal/mol, rm = 4.60u2009A)) and the I–Kru2009(Iu20093/2) potential (e = 0.36u2009kcal/mol, rm = 4.32u2009A) present shallower e’s, a larger rm, and stronger repulsive walls than the corresponding rare gas pair potentials. The results obtained from this and previous investigations are reviewed.

A crossed molecular beams investigation of the reactions O(3P)+ C6H6, C6D6

A crossed beams investigation of the reactions of O(3P)+C6H6, C6D6 has beeen carried out using a seeded, supersonic, atomic oxygen nozzle beam source. Angular and velocity distributions of reaction products have been used to identify the major reaction pathways. The initially formed triplet biradical, C6H6O (C6D6O), either decays by hydrogen (deuterium) elimination or becomes stabilized, most likely by nonradiative transition to the S0 manifold of ground state phenol. CO elimination was not found to be a major channel. The branching ratio between H(D) atom elimination and stabilization was found to be sensitive to both collision energy and isotopic substitution.