Probing the new bond in the vibrationally controlled bimolecular reaction of O with HOD(4νOH)

Photoelectron-photofragment coincidence ͑PPC͒ spectroscopy has been used to study the dissociative photodetachment of H 2 O 2 Ϫ and D 2 O 2 Ϫ . The observed partitioning of photoelectron and photofragment translational energies provides information on the dynamics in the transition state region of the reaction between two hydroxyl radicals: OHϩOH→O( 3 P)ϩH 2 O. The data reveal vibrationally resolved product translational energy distributions for both the entrance channel OHϩOH and the exit channel O( 3 P)ϩH 2 O upon photodetachment. The total translational energy distribution shows a convoluted vibrational progression consistent with antisymmetric stretch excitation of H 2 O in the exit channel and OH stretch in the entrance channel. The photoelectron spectra are compared to two-dimensional time-dependent wave packet dynamics simulations based on an anharmonic potential in the anion and a model collinear potential energy surface for the neutral complex. The PPC spectra also yield the dissociation energies D 0 (H 2 O 2 Ϫ →H 2 OϩO Ϫ ) ϭ1.15Ϯ0.08 eV and D 0 (D 2 O 2 Ϫ →D 2 OϩO Ϫ )ϭ1.05Ϯ0.08 eV.

Section: Introductionmentioning

confidence: 99%

Transition state dynamics of the OH+OH→O+H2O reaction studied by dissociative photodetachment of H2O2−

Deyerl

Clements

Luong

et al. 2001

“…In a series of experiments involving the reaction of H, Cl, and O atoms with HOD the groups of Crim [8][9][10][11][12][13] and Zare 14 -16 demonstrated that vibrational energy could be used to exert bond selectivity in reactions involving polyatomic reagents. In these experiments, vibrational excitation of the O-H stretch in HOD selectively enhanced the hydrogenabstraction channel, whereas the excitation of the O-D stretch led to the deuterium-abstraction channel.…”

Section: Introductionmentioning

confidence: 99%

Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

Bechtel

Kim

Camden

et al. 2004

The title reaction is investigated by co-expanding a mixture of Cl2 and CH2D2 into a vacuum chamber and initiating the reaction by photolyzing Cl2 with linearly polarized 355 nm light. Excitation of the first C-H overtone of CH2D2 leads to a preference for hydrogen abstraction over deuterium abstraction by at least a factor of 20, whereas excitation of the first C-D overtone of CH2D2 reverses this preference by at least a factor of 10. Reactions with CH2D2 prepared in a local mode containing two quanta in one C-H oscillator /2000>- or in a local mode containing one quantum each in two C-H oscillators /1100> lead to products with significantly different rotational, vibrational, and angular distributions, although the vibrational energy for each mode is nearly identical. The Cl+CH2D2/2000>- reaction yields methyl radical products primarily in their ground state, whereas the Cl+CH2D2/1100> reaction yields methyl radical products that are C-H stretch excited. The HCl(v=1) rotational distribution from the Cl+CH2D2/2000>- reaction is significantly hotter than the HCl(v=1) rotational distribution from the Cl+CH2D2/1100> reaction, and the HCl(v=1) differential cross-section (DCS) of the Cl+CH2D2/2000>- reaction is more broadly side scattered than the HCl(v=1) DCS of the Cl+CH2D2/1100> reaction. The results can be explained by a simple spectator model and by noting that the /2000>- mode leads to a wider cone of acceptance for the reaction than the /1100> mode. These measurements represent the first example of mode selectivity observed in a differential cross section, and they demonstrate that vibrational excitation can be used to direct the reaction pathway of the Cl+CH2D2 reaction.

“…For systems involving polyatomic reagents, the extra degrees of freedom associated with polyatomics can complicate this simple picture and lead to a large number of different vibrational motions. Several groups [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] have demonstrated that excitation of certain vibrational motions can localize energy in specific parts of the polyatomic reagent and lead to dramatic bond-and mode-selectivity. [17][18][19] The first examples of such behavior involved reactions of fast H atoms with various isotopes of water.…”

Section: Introductionmentioning

confidence: 99%

Comparing the dynamical effects of symmetric and antisymmetric stretch excitation of methane in the Cl+CH4 reaction

Bechtel

Camden

Brown

et al. 2004

The effects of two nearly isoenergetic C-H stretching motions on the gas-phase reaction of atomic chlorine with methane are examined. First, a 1:4:9 mixture of Cl(2), CH(4), and He is coexpanded into a vacuum chamber. Then, either the antisymmetric stretch (nu(3)=3019 cm(-1)) of CH(4) is prepared by direct infrared absorption or the infrared-inactive symmetric stretch (nu(1)=2917 cm(-1)) of CH(4) is prepared by stimulated Raman pumping. Photolysis of Cl(2) at 355 nm generates fast Cl atoms that initiate the reaction with a collision energy of 1290+/-175 cm(-1) (0.16+/-0.02 eV). Finally, the nascent HCl or CH(3) products are detected state-specifically via resonance enhanced multiphoton ionization and separated by mass in a time-of-flight spectrometer. We find that the rovibrational distributions and state-selected differential cross sections of the HCl and CH(3) products from the two vibrationally excited reactions are nearly indistinguishable. Although Yoon et al. [J. Chem. Phys. 119, 9568 (2003)] report that the reactivities of these two different types of vibrational excitation are quite different, the present results indicate that the reactions of symmetric-stretch excited or antisymmetric-stretch excited methane with atomic chlorine follow closely related product pathways. Approximately 37% of the reaction products are formed in HCl(v=1,J) states with little rotational excitation. At low J states these products are sharply forward scattered, but become almost equally forward and backward scattered at higher J states. The remaining reaction products are formed in HCl(v=0,J) and have more rotational excitation. The HCl(v=0,J) products are predominantly back and side scattered. Measurements of the CH(3) products indicate production of a non-negligible amount of umbrella bend excited methyl radicals primarily in coincidence with the HCl(v=0,J) products. The data are consistent with a model in which the impact parameter governs the scattering dynamics.