30 research outputs found
The Multiplexed Chemical Kinetic Photoionization Mass Spectrometer: A New Approach To Isomer-resolved Chemical Kinetics
We have developed a multiplexed time- and photon-energy?resolved photoionizationmass spectrometer for the study of the kinetics and isomeric product branching of gasphase, neutral chemical reactions. The instrument utilizes a side-sampled flow tubereactor, continuously tunable synchrotron radiation for photoionization, a multi-massdouble-focusing mass spectrometer with 100percent duty cycle, and a time- and positionsensitive detector for single ion counting. This approach enables multiplexed, universal detection of molecules with high sensitivity and selectivity. In addition to measurement of rate coefficients as a function of temperature and pressure, different structural isomers can be distinguished based on their photoionization efficiency curves, providing a more detailed probe of reaction mechanisms. The multiplexed 3-dimensional data structure (intensity as a function of molecular mass, reaction time, and photoionization energy) provides insights that might not be available in serial acquisition, as well as additional constraints on data interpretation
The multiplexed chemical kinetic photoionization mass spectrometer: A new approach to isomer-resolved chemical kinetics
Thermochemistry and Kinetics of the Reaction of 1-Methylallyl Radicals with Molecular Oxygen
Molecular Dynamics Simulation of C–C Bond Scission in Polyethylene and Linear Alkanes: Effects of the Condensed Phase
The
reaction of C–C bond scission in polyethylene chains
of various lengths was studied using molecular dynamics under the
conditions of vacuum and condensed phase (polymer melt). A method
of assigning meaningful rate constant values to condensed-phase bond
scission reactions based on a kinetic mechanism accounting for dissociation,
reverse recombination, and diffusional separation of fragments was
developed. The developed method accounts for such condensed-phase
phenomena as cage effects and diffusion of the decay products away
from the reaction site. The results of C–C scission simulations
indicate that per-bond rate constants decrease by an order of magnitude
as the density of the system increases from vacuum to the normal density
of a polyethylene melt. Additional calculations were performed to
study the dependence of the rate constant on the length of the polymer
chain under the conditions of the condensed phase. The calculations
demonstrate that the rate constant is independent of the degree of
polymerization if polyethylene samples of different lengths are kept
at the same pressure. However, if instead molecular systems of different
polyethylene chain lengths decompose under the conditions of the same
density, shorter chains result in higher pressures and lower rate
constants. The observed effect is attributed to a higher degree of
molecular crowding (lower fraction of free intermolecular space available
for molecular motion) in the case of shorter molecules