For several decades, the influence of Two State Reactivity (TSR) has been implicated in a host of reactions, but has lacked a stand-alone, definitive experimental kinetic signature identifying its occurrence....

The study of gas-phase ion-molecule reactions has been influential in the investigation of transition metal mediated bond activation and catalysis. We have furthered this field by developing a new technique capable of measuring the microcanonical kinetics for reactions between transition metal cations and neutral organic molecules. This novel method has been designated as single photon initiated dissociative rearrangement reaction (SPIDRR) technique and provides a nearly direct measurement of microcanonical reaction rate constants. For this reason, SPIDRR offers unique insight into reaction mechanisms and dynamics by assessing the energy dependence of the microcanonical rate constant, as well as measuring product branching fractions and kinetic isotope effects. The following paper provides a detailed overview of SPIDRR and its advantages in the field of gas-phase catalysis research.

Rate constants and product branching fractions were measured for reactions of Ar+, O2 +, and NO+ with isoprene (2-methyl-1,3-butadiene C5H8) as a function of temperature. The rate constants are large (∼2 × 10–9 cm3 s–1) and increase with temperature, exceeding the ion-dipole/induced dipole capture rate. Adding a hard sphere term to the collision rate provides a more useful upper limit and predicts the positive temperature dependences. Previous kinetic energy-dependent rate constants show a similar trend. NO+ reacts only by non-dissociative charge transfer. The more energetic O2 + reaction has products formed through both non-dissociative and dissociative charge transfer, or possibly through an H atom transfer. The very energetic Ar+ has essentially only dissociative products; assumption of statistical behavior in the dissociation reasonably reproduces the product branching fractions.

The rate constant for electron attachment to Mo(CO)6 was determined to be ka = 2.4 ± 0.6 × 10−7 cm3 s−1 at 297 K in a flowing-afterglow Langmuir-probe experiment. The sole anion product is Mo(CO)5−. A small decline in ka was observed up to 450 K, and decomposition was apparent at higher temperatures. The charge transfer reaction of Ar+ with Mo(CO)6 is exothermic by 7.59 ± 0.03 eV, which appears to be sufficient to remove the first 5 ligands from Mo(CO)6+.