A Velocity Map Ion-imaging Study on Ketene Photodissociation at 218 nm

Photodissociation dynamics of ketene at 218 nm has been investigated using the velocity map ion-imaging method. Both angular and translational energy distributions for the CO products at different rotational and vibrational states have been obtained. The 2＋1 REMPI spectrum of CO products is also obtained. The results are as bellow： （i） CO products in the first two vibrational states （ v＂=0 and v＂=1 ） exhibit significant rotational excitation. Furthermore the rotational excitation of CO at the v＂=0 level is noticeably higher than that at the v＂=1 level. （ii） It was found that the major photodissociation pathway of ketene at 218 nm is the CH2（ǎ^1A1）＋CO（X^1∑^＋） channel, while the CH2（b^1B1）＋CO（X^1∑^＋） channel and the CH2（X^3B1）＋CO（X^1E^＋） channel are also likely present, （iii） The anisotropy parameters β of CO different rovibronic states all appear to be larger than zero. No significant difference is observed at the two vibrational states,

Imaging Photodissociation Dynamics of MgO at 193 nm

In this work,we used time-sliced ion velocity imaging to study the photodissociation dynamics of Mg O at 193 nm.Three dissociation pathways are found through the speed and angular distributions of magnesium.One pathway is the one-photon excitation of Mg O(X^(1)∑^(+))to Mg O(G^(1)Π)followed by spin-orbit coupling between the G^(1)Π,3^(3)Πand ^(1^(5))Πstates,and finally dissociated to the Mg(^(3)Pu)+O(^(3)Pg)along the 1^(5)Πsurface.The other two pathways are one-photon absorption of Mg O(A^(1)Π)state to Mg O(G^(1)Π)and Mg O(4^(1)Π)state to dissociate into Mg(^(3)P_(u))+O(^(3)P_(g))and Mg(^(1)S_(g))+O(^(1)S_(g)),respectively.The anisotropy parameters of the dissociation pathways are related to the lifetime of the vibrational energy levels and the coupling of rotational and vibronic spin-orbit states.The total kinetic energy analysis gives D0(Mg-O)=21645±50 cm^(-1).

UV Photodissociation Dynamics of Nitric Acid： The Hydroxyl Elimination Channel

Sliced velocity mapping ion imaging technique was employed to investigate the dynamics of the hydroxyl elimination channel in the photodissociaiton of nitric acid in the ultraviolet region. The OH product was detected by （2＋1） resonance enhanced multiphoton ionization via the D^2∑^- electronic state. The total kinetic energy spectra of the OH＋NO2 channel from the photolysis of HONO2 show that both ：NO2（X2A1） and NO2（A2B2） channels are present, suggesting that both 1^1A″ and 2^1A″ excited electronic states of HONO2 are involved in the excitation. The parallel angular distributions suggest that the dissociation of the nitric acid is a fast process in comparison with the rotational period of the HNO3 molecule. The anisotropy parameter β for the hydroxyl elimination channel is found to be dependent on the OH product rotational state as well as the photolysis energy.

Advanced Techniques for Quantum-State Specific Reaction Dynamics of Gas Phase Metal Atoms

One of the themes of modern molecular reac tion dynamics is to charac terize elementary chemical reactions from“quan tum state to quan tum stat e”,and the study of molecular reaction dynamics in excited states can help test the validi ty of modern chemical t heories and provide met hods to cont rol chemical reactions.The subject of this review is to describe the recent experimental techniques used to study the reaction dynamics of metal atoms in the gas phase.Through these techniques,information such as the internal energy distribution and angular distribution of the nascent products or the three-dimensional stereodynamic reactivity can be obtained.In addition,by preparing metal at oms wi th specific exci ted elec tronic states or orbi tal arrangemen ts,information about the reactivity of the electronic states enriches the relevant understanding of the electron transfer mechanism in metal reaction dynamics.

Photodissociation Dynamics of AlO at 193 nm using Time-Sliced Ion Velocity Imaging

The photodissociation dynamics of Al O at 193 nm is studied using time-sliced ion velocity mapping.Two dissociation channels are found through the speed and angular distributions of aluminum ions:one is one-photon dissociation of the neutral AlO to generate Al(2 Pu)+O(3 Pg),and the other is two-photon ionization and then dissociation of AlO^+to generate Al^+(1 Sg)+O(3 Pg).Each dissociation channel includes the contribution of AlO in the vibrational states v=0-2.The anisotropy parameter of the neutral dissociation channel is more dependent on the vibration state of AlO than the ion dissociation channel.

Imaging Reaction Dynamics of Y+SO2

The reaction dynamics of yttrium atoms with sulfur dioxide molecules at a high collision energy of 36 kcal/mol was studied using time-sliced velocity map ion imaging,crossed molecular beam and laser-ablation method.The product YO was detected via multiphoton ionization at various wavelengths in the region of 482-615 nm.The slice images of YO show a broad velocity distribution and forward-backward peaking angular distribution.The forward scattering signal is stronger than its backward distribution.This indicates that the reaction proceeds via an intermediate complex and the lifetime of the intermediate state is less than one rotational period.The formation of complex suggests that electron transfer occurs in the oxidation reaction.

Imaging the Dissociation Dynamics of Si2+ via Two-Photon Excitation at 193 nm

In the one-color experiment at 193nm, we studied the photodissociation of Si2+ ions prepared by two-photon ionization using the time-sliced ion velocity map imaging method. The Si+ imaging study shows that Si2+ dissociation results in two distinct channels: Si(3Pg)+Si+(2Pu) and Si(1D2)+Si+(2Pu). The main channel Si(3Pg)+Si+(2Pu)) is produced by the dissociation of the Si2+ ions in more than one energetically available excited electronic state, which are from the ionization of Si2(v=0-5). Particularly, the dissociation from the vibrationally excited Si2(v=1) shows the strongest signal. In contrast, the minor Si(1D2)+Si+(2Pu) channel is due to an avoided crossing between the two 22Πg states in the same symmetry. It has also been observed the one-photon dissociation of Si2+(X4Σg-) into Si(1D2)+Si+(2Pu) products with a large kinetic energy release.

Photodissociation Dynamics of Methanol and Ethanol at 157 nm

157 nm photodissociation of jet-cooled CH3OH and C2HsOH was studied using the high-n Rydberg atom time-of-flight （TOF） technique. TOF spectra of nascent H atom products were measured. Simulation of these spectra reveals three different atomic H loss processes： one from hydroxyl H elimination, one from methyl （ethyl） H elimination, and one from secondary dissociation of the methoxy （ethoxy） radical. The relative branching ratio indicates secondary dissociation of ethoxy is less important than that of methoxy. The average angular anisotropy parameter of methanol is negative （with β≈-0.3）, indicating the transition dipole moment is perpendicular to the C-O-H plane. The slightly more negative β value of ethanol （with β≈-0.4） implies that ethanol has a longer rotational period. These experimental results indicate that both systems undergo fast internal conversion to the 3s surface after it is excited to the 3px surface, and then dissociate on the 3s surface. The translational energy distribution of the CH3O＋H products reveals extensive CH3 rocking or CH3 umbrella excitation in the CH30 radical. However the vibrational structures are not resolved in the C2H5O radical.