NO(X 2Π) product state distributions in molecule–surface collision-induced dissociation: Direct inelastic scattering of n,i-C3F7NO from MgO(100) at Eincident≤7.0 eV

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Abstract
Molecule–surface collision‐induced dissociation (CID) has been studied for n‐C3F7NO and i‐C3F7NO molecular beams scattered from MgO(100) at incident kinetic energies (Eincident) up to 7 eV. The NO fragment was detected state selectively using two‐photon, two‐frequency ionization, and rotational and spin–orbit distributions are reported for several Eincident values. State and angle‐resolved signals were integrated to give CID yields, which increased sharply with Eincident . In most cases, rotational excitation could be described by separate temperatures for each spin–orbit state. The upper 2∏3/2 state was underpopulated relative to statistical predictions (e.g., for n‐C3F7NO at Eincident =5.0 eV, the spin–orbit temperature was ∼170 K, while Trot was ∼500 K). The CID results are compared to NO state distributions derived from the photodissociation of expansion‐cooled molecules under collision‐free conditions, at different energies (E°) above D0. These distributions were measured for both n‐C3F7NO and i‐C3F7NO up to E°∼4500 cm−1, and rotational excitation within each spin–orbit state was statistical, except at E°≥3000 cm−1. As with CID, a low [2∏3/2]/[2∏1/2] ratio was observed, and the reaction mechanism is probably unimolecular decomposition via the lowest triplet surface T1 with little or no exit channel barrier. The pronounced similarities between the CID and photodissociation results suggest that common reaction mechanisms may be operative. All of the CID results are compatible with direct inelastic scattering followed by unimolecular reaction on the S0 and/or T1 potential surfaces.