Molecular beams of ICl in selected rotational states with positive effective electric dipole moments have been produced using a new electrostatic alternate gradient focuser (AGF). It has been possible to select the states ‖J,M〉=‖0,0〉, ‖1,±1〉, and ‖2,±2〉. The experimental arrangement consists of a seeded supersonic nozzle beam source for ICl, the AGF selector based on four-wire fields, and a quadrupole mass filter detector with electron bombardement ionizer. The velocity selector, usually used in state selection experiments, could be eliminated because of the narrow velocity distribution (Δv/v?0.05) of the ICl beam. On account of the strong rotational cooling during the nozzle beam expansion, the relative populations of lower J states are increased substantially. An additional advantage of the seeded beam technique is the possibility of changing the velocity of the state-selected molecules by choosing a suitable noble gas mixture. The flux density of the state-selected ‖1,±1〉 beam exceeds that of the direct unfocused beam; its absolute value is estimated to be greater than 3×1012 molecules cm−2 s−1.

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The oxidation of benzene has been investigated with a high-temperature alumina flow reactor in the temperature range of 950-1150 K at residence times of ca. 1 ms and pressures of ca. 400 mbar. Analysis of the reaction products at various stages of the reaction was carried out by direct expansion of the reacting gas yielding a molecular beam that was analyzed by a mass spectrometer. Product identification studies were made by comparing the results from the oxidations of C6H, and C6D6. Besides the products found in previous studies a number of new oxygenated intermediate species were identified, namely benzoquinone, cyclopentadienone, acrolein, and a C,H,O species.In addition, some higher hydrocarbons have been found even a t high oxygen excess. The role of the intermediates within the current ideas of the reaction mechanism is discussed.