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Notes: 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.

Notes: The title reaction was examined for incident kinetic energies in the range 3–7 eV and surface temperatures in the range 500–800 K; dissociation probabilities as high as 3±1% were measured. NO state distributions were obtained near the specular angle using two-photon, two-frequency laser ionization, and spin–orbit "temperatures''∼170 K were observed, in contrast to higher rotational excitations. Possible mechanisms are mentioned.

Notes: The collisional insertion of Cs+ ions into surface adsorbed C60 molecules was studied by scattering Cs+ ion beams from a C60 layer deposited on gold over the 35–220 eV impact energy range. Both Cs@C60+ and C60+ ions were ejected from the surface following the Cs+ impact but each species was characterized by different impact energy dependent yields and internal temperatures. Clear evidence for the endohedral nature of the complex is given. Both the scattering dynamics (at impact energies up to ∼100 eV) and the instant rise of the Cs@C60+ signal with the Cs+ beam onset clearly demonstrate that the insertion/ejection process is basically a single collision event. The outgoing Cs@C60+ and C60+ ions fragment during their flight time, after leaving the surface, via sequential emission of C2 units down to Cs@C50+ and C44+, respectively. Relative impact energy dependent yields were measured for both parent species and for all fragments. The yield curves are kinetically shifted with respect to each other as expected. Comparing the impact energy dependent fragmentation patterns of C60+ and Cs@C60+ we conclude that the ejected Cs@C60+ ion is much hotter than the C60+ ion. The internal vibrational excitation for both species is reaching a maximal value around 90–110 eV impact energy and than gradually decreases with increase in impact energy. The integrated Cs@C60+ yield is strongly peaked at around 80±5 eV impact energy. At impact energies above 120 eV also a C60− signal is observed but no Cs@C60− could be detected. © 2002 American Institute of Physics.

Notes: A method of generating effusive molecular beams of C60 with vibrational temperatures up to 2000 K is presented. Direct measurement of the thermal stability and fragmentation kinetics of C60 in the range of 1100–1970 K, on the milliseconds time scale, provides thermal rate constants k(T)=10–300 s−1 (for T=1720–1970 K, respectively) and activation energy of E0=4.0±0.3 eV.

Notes: We have studied the dependence of electron impact induced ionization and fragmentation of C60 molecules in effusive molecular beams upon the initial thermal excitation in the temperature range of 1190–1875 K, corresponding to an average vibrational energy of 10–20 eV. This is the largest energy range of parent molecule thermal excitation ever reported for electron-impact mass-spectrometric studies. The normalized curves of electron energy (Ee) dependent ion currents of C+60 and C+58 were measured and analyzed for the temperatures (T0) of 1190, 1435, 1570, 1695, and 1875 K. Similar measurements were done for C+2n (n=26–28) fragments for T0=1190 and 1875 K. We have developed an expression for the dependence of C+58 fragment ion current i58(Ee,T0), formed via the decay process C+60→C+58+C2, on electron energy and initial temperature. Using this expression and the strong temperature dependence observed, we have proposed a simple experimental method for estimating the energy deposition function—the probability density of vibrational excitation ε by an ionizing electron of energy Ee. The effective (apparent) value of maximum deposited energy was found to be εm(Ee)=Ee−E*, where E*=30±5 eV. Possible interpretations for this surprisingly low value are discussed. Comparing the experimental i58(Ee,T0) curves with the calculated ones over the range of Ee=30–80 eV we find that for T0≤1600 K, good agreement is obtained assuming that the C60 initial internal excitation is determined by the source temperature alone.For the higher temperature range 1600 K≤T0≤1900 K, we had to use a modified calculation taking into account radiative cooling and ensemble evaporative cooling processes along the molecular beam flight path. As a result, we have obtained an accurate simulation of the complete family of i58(Ee,T0) curves over all the temperature range measured, using a single set of independently measured physical quantities, and without any adjustable parameter. Uniqueness and sensitivity were thoroughly checked and demonstrated. The good agreement between experiment and calculation basically confirms our description of the underlying process and provides an additional support for the values of the independent physical parameters used. We have used maximum energy deposition parameter of E*=31 eV, an activation energy of E0=4.3–4.5 eV for the neutral fragmentation channel C60→C58+C2 and E1=4.0 eV for the ion fragmentation channel C+60→C+58+C2, and pre-exponential factors of A0=A1=2.5×1013 s−1. These values are very close to former ones obtained by us from analysis of time-of-flight distributions and integrated flux decay measurements of hot C60 molecular beams. Correspondence with other results reported in the literature is discussed and a two-step dissociation mechanism is proposed. © 1995 American Institute of Physics.