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Electron attachment lineshapes, cross sections and rate constants are reported for the molecules CH2Br2, CF2Br2, CF3Br, CBrCl3, BrCN, C2H2Br4, CH3I, C2H5I and 1, 1, 1,-C2Cl3F3. Use is made of the krypton photoionisation method. In addition, the signal intercomparison technique is used to obtain individual channel cross sections and rate constants for Br- and CN-- formation from BrCN, and for Br- and Br2- formation from CF2Br2. Present results in 1,1,1,-C2Cl3F3 using a new ion extraction grid geometry are compared with earlier results, and differences discussed in terms of the electric field equipotentials of two extraction systems used in the present work. Approximate potential energy curves for BrCN are presented, and the temperature dependence of the Br- channel cross section discussed.

First results of a beam-beam, single-collision study of negative-ion mass spectra produced by attachment of zero-energy electrons to the molecules of the explosives RDX, PETN, and TNT are presented. The technique used is reversal electron attachment detection (READ) wherein the zero-energy electrons are produced by focusing an intense electron beam into a shaped electrostatic field which reverses the trajectory of electrons. The target beam is introduced at the reversal point, and attachment occurs because the electrons have essentially zero longitudinal and radial velocity. The READ technique is used to obtain the "signature" of molecular ion formation and/or fragmentation for each explosive. Present data are compared with results from atmospheric-pressure ionization and negative-ion chemical ionization methods.

From accurate spectroscopic constants one finds that the thermal dissociative-attachment process (DA) in DI should be exothermic only for rotational levels J& 8 in U =0. We report herein measurement of an enhancement of DA with rotational temperature T in the range 298 -468 K. The effect is easily accounted for by the increase in total fractional population of excited J levels in DI relative to HI. The effect affords a rotational analog to the use of uibrationally excited molecules (e.g. , HCl) in a plasma to control electron conduction.

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