No abstract

No abstract

Kinetic energy releases (KERs) in unimolecular fragmentations of singly and multiply charged ions provide information concerning ion structures, reaction energetics and dynamics. This topic is reviewed covering both early and more recent developments. The subtopics discussed are as follows: (1) introduction and historical background; (2) ion dissociation and kinetic energy release: kinematics; potential energy surfaces; (3) the kinetic energy release distribution (KERD); (4) metastable peak observations: measurements on magnetic sector and time-of-flight instruments; energy selected results by photoelectron photoion coincidence (PEPICO); (5) extracting KERDs from metastable peak shapes; (6) ion structure determination and reaction mechanisms: singly and multiply charged ions; biomolecules and fullerenes; (7) theoretical approaches: phase space theory (PST), orbiting transition state (OTS)/PST, finite heat bath theory (FHBT) and the maximum entropy method; (8) exit channel interactions; (9) general trends: time and energy dependences; (10) thermochemistry: organometallic reactions, proton-bound clusters, fullerenes; and (11) the efficiency of phase space sampling.

No abstract

No abstract

No abstract

An in-line double mass spectrometer has been employed to determine reaction rate coefficients and excitation functions for several types of negative ion reactions involving ozone. The interactions studied include electron transfer reactions, such as, M−+O3→M+O3− (where M−=O−, OH−, F−, Cl−, Br−, I−, S−, SH−, Cl−2, C2H−, NO2−, and CO3−) and particle transfer reactions, such as MO−+O2→M+O3− (where MO−=O2−, NO2−, NO3−, CO3−). Translational energy thresholds have been determined for those reactions which are endothermic by applying exact Doppler corrections for the thermal motion of the neutral as well as corrections for the translational energy distribution of the projecticle ions. These experiments place a lower limit of 2.26+0.04−0.06 eV on the electron affinity of ozone. This value is in excellent agreement with the value computed from the bond dissociation energy of O3− in its most stable configuration, D00(O−–O2) =1.80 eV, as deduced from measurements of the translational energy thresholds for the collisional dissociation process, O−3+M→O−+O2+M, where M=He, Ar. Further implications of these experiments with respect to the structure, thermochemistry, and excited states of O−3 are discussed.

Unimolecular fragmentations of the anthracene and phenanthrene radical cations C14H10 •+ were studied by time-resolved photoionization in the vacuum UV, RRKM/QET calculations, and MS/MS with electron ionization. The primary reactions observed are parallel H•, H2, C2H2, C3H3 •, and C4H2 losses, as well as two consecutive H• losses from C14H9 + and C12H8 •+, respectively. Appearance energies were determined for the microsecond and millisecond time ranges. Activation parameters were deduced for the reactions. The H• and C2H2 loss reactions are characterized by loose transition states. The following heats of formation were deduced:  ΔH f0° (C14H9 +, anthracenyl) = 282.0 ± 3.0 kcal/mol, ΔH f0°(C14H9 +, phenanthrenyl) = 276.4 ± 3.0 kcal/mol and ΔH f0°(C12H8 •+, biphenylene) ≤ 281.7 ± 3.0 kcal/mol. The C−H bond energies in the anthracene and phenanthrene radical cations are 4.38 ± 0.08 and 3.92 ± 0.10 eV, respectively. The role of isomerization of the parent radical cations prior to dissociation will be discussed.