13 research outputs found
Imaging the quantum-state specific differential cross sections of HCl formed from reactions of chlorine atoms with methanol and dimethyl ether
Center-of-mass frame scattering angle distributions obtained directly from crossed molecular beam velocity map images are reported for HCl formed in different rotational levels of its vibrational ground state by reaction of Cl atoms with CH<sub>3</sub>OH and CH<sub>3</sub>OCH<sub>3</sub>. Products are observed to scatter over all angles, with peaks in the distribution in the forward and backward directions (θ = 0 and 180° with respect to the relative velocity vectors of the Cl atoms). Products of both reactions exhibit differential cross sections that vary with the rotational quantum number of the HCl, with a greater propensity for forward scatter for J = 2, shifting to more pronounced backward scatter for J = 5. This trend is, however, more evident for reaction of dimethyl ether than for methanol. The mean fractions of the available energy channeled into product kinetic energy vary with scattering angle, but the angle-averaged fractions are, respectively, 0.37 and 0.42 for the methanol and dimethyl ether reactions. On average, 46% or more of the available energy of the reactions becomes internal energy of the radical co-product. Results are interpreted with the aid of computed energies of transition states and molecular complexes along the reaction pathways, and comparisons are drawn with recent measurements of the scattering distributions and energy release for reactions of Cl atoms with small alkanes
The dynamics of the Cl+n-C4H10-->HCl (v',j') + C4H9 reaction at 0.32 eV.
Rotational state resolved center-of-mass angular scattering and kinetic energy release distributions have been determined for the HCl (v' = 0, j' = 0-6) products of the reaction of chlorine with n-butane using the photon-initiated reaction technique, coupled with velocity-map ion imaging. The angular and kinetic energy release distributions derived from the ion images are very similar to those obtained previously for the Cl plus ethane reaction. The angular distributions are found to shift from forward scattering to more isotropic scattering with increasing HCl rotational excitation. The kinetic energy release distributions indicate that around 30% of the available energy is channeled into internal excitation of the butyl radical products. The data analysis also suggests that H-atom abstraction takes place from both primary and secondary carbon atom sites, with the primary site producing rotationally cold, forward scattered HCl (v' = 0) products, and the secondary site yielding more isotropically scattered HCl (v' = 0) possessing higher rotational excitation. The mechanisms leading to these two product channels are discussed in the light of the present findings, and in comparison with studies of other Cl plus alkane reactions
The dynamics of the Cl+n-C4H10-->HCl (v',j') + C4H9 reaction at 0.32 eV.
Rotational state resolved center-of-mass angular scattering and kinetic energy release distributions have been determined for the HCl (v' = 0, j' = 0-6) products of the reaction of chlorine with n-butane using the photon-initiated reaction technique, coupled with velocity-map ion imaging. The angular and kinetic energy release distributions derived from the ion images are very similar to those obtained previously for the Cl plus ethane reaction. The angular distributions are found to shift from forward scattering to more isotropic scattering with increasing HCl rotational excitation. The kinetic energy release distributions indicate that around 30% of the available energy is channeled into internal excitation of the butyl radical products. The data analysis also suggests that H-atom abstraction takes place from both primary and secondary carbon atom sites, with the primary site producing rotationally cold, forward scattered HCl (v' = 0) products, and the secondary site yielding more isotropically scattered HCl (v' = 0) possessing higher rotational excitation. The mechanisms leading to these two product channels are discussed in the light of the present findings, and in comparison with studies of other Cl plus alkane reactions
The dynamics of the Cl+C2H6 -> HCl(v ',j ')+C2H5 reaction at 0.24 eV: Is ethyl a spectator?
The hydrogen atom abstraction reaction between Cl(2P3/2) and ethane was studied at a mean collision energy of 0.24 eV. Single beam experiments revealed both center-of-mass angular and energy release distributions
Slice imaging of the photodissociation of acetaldehyde at 248 nm. Evidence of a roaming mechanism
The photodissociation of acetaldehyde in the molecular channel yielding CO and CH4 at 248 nm
has been studied, probing different rotational states of the CO(n = 0) fragment by slice ion
imaging using a 2+1 REMPI scheme at around 230 nm. From the slice images, clear evidence of
the co-existence of two different mechanisms has been obtained. One of the mechanisms is
consistent with the well-studied conventional transition state in which CO products appear rotationally
excited, and the second is consistent with a roaming mechanism. This roaming mechanism is
characterized by a low rotational energy disposal into the CO fragment as well as by a very low
kinetic energy release, corresponding to a high internal energy in the CH4 counter-fragment
Photofragment slice imaging studies of pyrrole and the Xe..pyrrole cluster
The photolysis of pyrrole has been studied in a molecular beam at wavelengths of 250, 240, and
193.3 nm, using two different carrier gases, He and Xe. A broad bimodal distribution of H-atom
fragment velocities has been observed at all wavelengths. Near threshold at both 240 and 250 nm,
sharp features have been observed in the fast part of the H-atom distribution. Under appropriate
molecular beam conditions, the entire H-atom loss signal from the photolysis of pyrrole at both 240
and 250 nm including the sharp features disappear when using Xe as opposed to He as the carrier
gas. We attribute this phenomenon to cluster formation between Xe and pyrrole, and this assumption
is supported by the observation of resonance enhanced multiphoton ionization spectra for the
Xe¯pyrrole cluster followed by photofragmentation of the nascent cation cluster. Ab initio
calculations are presented for the ground states of the neutral and cationic Xe¯pyrrole clusters as
a means of understanding their structural and energetic properties