Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session A11: Focus Session: Promises and Challenges in Chemical Dynamics I |
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Sponsoring Units: DCP Chair: Malcolm Bersohn, University of Toronto Room: Baltimore Convention Center 303 |
Monday, March 13, 2006 8:00AM - 8:36AM |
A11.00001: Symmetry breaking and coherent control: the importance of the envelope Invited Speaker: I shall review the progress of the field of ``coherent control,'' according to which control of dynamical processes is achieved by using lasers to induce (destructive or constructive) interferences between different quantum pathways leading to the same final outcome. I shall then discuss symmetry breaking stimulated by external laser fields and the role played by the relative and the ``envelope'' phase. Applications to chiral purification and the control of photo-current directionality in semiconductors will be given. [Preview Abstract] |
Monday, March 13, 2006 8:36AM - 8:48AM |
A11.00002: Coherent Phase Control of the Ionization and Dissociation of Vinyl Chloride Robert J. Gordon, Vishal J. Barge, Zhan Hu, Joyce Willig Two-pathway quantum interference was used to control the photochemical reactions of vinyl chloride (C$_{2}$H$_{3}$Cl, VCl). A molecular beam of VCl was irradiated simultaneously with 532 and 177 nm laser light, produced from the second and sixth harmonics of a Nd:YAG laser. The relative phase of the visible and UV lasers was adjusted by passing them through a cell containing a variable pressure of hydrogen gas, and the parent and fragment (C$_{2}$H$_{3}$ and HCl) ions of VCl were detected with a time-of-flight mass spectrometer. The phase lags between different pairs of modulated ion signals depended on the location of the laser focus. This variation of the phase lags was produced by the axial spatial phase of the focused laser beam. A non-zero phase lag between the parent and fragment ions produced when the laser was focused in the center of the spectrometer slit is indicative of coherent control of the branching between ionization and dissociation. [Preview Abstract] |
Monday, March 13, 2006 8:48AM - 9:00AM |
A11.00003: Reaction Control through Coherent Excitation of a Superposition State: Resonant Multiphoton Dissociation-Ionization of Sulfur Dioxide Bing Xue, Jun Han, Hai-Lung Dai Through coherent excitation of a pair of eigenlevels, an oscillation of 130 kcal/mole in energy excitation between electronic and vibrational motions on nano second time scale is created for the molecule sulfur dioxide. The reactivity of the molecule can be influenced depending on whether the molecule is vibrationally or electronically excited with this large amount of energy. The effect of excitation on reactivity is demonstrated in resonance enhanced multiphoton dissociation-ionization of sulfur dioxide as a function of time following the coherent excitation. [Preview Abstract] |
Monday, March 13, 2006 9:00AM - 9:36AM |
A11.00004: Recent Developments in Radiationless Transitions Invited Speaker: |
Monday, March 13, 2006 9:36AM - 9:48AM |
A11.00005: Energy transfer of highly vibrationally excited azulene: crossed-beam study of collisions between azulene and krypton Chi-Kung Ni The energy transfer dynamics between highly vibrationally excited azulene molecules and Kr atoms in a series of collision energies was studied using a crossed-beam apparatus along with time-sliced velocity map ion imaging techniques. The shapes of the collisional energy-transfer probability distribution functions were measured directly from the scattering results of highly vibrationally excited or ``hot'' azulene. At low enough collision energies an azulene-Kr complex was observed, resulting from small amounts of translational to vibrational/rotational (T-V/R) energy transfer. T-V/R energy transfer was found to be quite efficient. On the other hand, only a small fraction of vibrational energy is converted to translational energy (V-T). We find that substantial amounts of energy are transferred in the backward scattering direction due to supercollisions at high collision energies. [Preview Abstract] |
Monday, March 13, 2006 9:48AM - 10:00AM |
A11.00006: Systematic degeneracies as a guide to the vibrational dynamics of methanol David Perry The vibrational dynamics of the CH stretch and torsional vibrations of methanol are explored using a 4-dimensional effective Hamiltonian. The model parameters are constrained by a combination of low-resolution and high-resolution spectral data. At low excitation energies, the torsion-vibration states are at most 2-fold degenerate as expected for the combination of the E-type torsional tunneling species with the A' and A'' (in Cs) CH stretch vibrations. At high torsional energies, we find a series of approximate 4-fold degeneracies characteristic of a degenerate E-type asymmetric CH stretch in combination with the decoupled degenerate free internal rotation. When a single CH bond is excited to a high level, torsional tunneling is quenched causing all such levels to be 3-fold degenerate. When both a local CH stretch and internal rotation are highly excited, we find systematic 6-fold degeneracies characterized by free internal rotation decoupled from three equivalent local CH stretches. The transition regions between these simple limiting behaviors are explored. [Preview Abstract] |
Monday, March 13, 2006 10:00AM - 10:12AM |
A11.00007: Vibrationally Enhanced Reactions of Highly Excited Pyridine-d$_{5}$ (E$_{vib}$=38,000 cm$^{-1}$) with Cl Radicals Amy Mullin, Ziman Li, Qingnan Liu High resolution transient IR probing of DCl reaction products at 4.9 $\mu $m is used to study the influence of large amounts of internal energy on D-atom abstraction reactions of pyridine-d$_{5}$ (E$_{vib}$=38,100 cm$^{-1})$ with Cl radicals. Vibrationally hot pyridine-d$_{5}$ molecules are prepared using 266 nm pulsed excitation and Cl radicals are generated by photodissociation of Cl$_{2}$ at 355 nm. Cl radicals undergo collisions with pyridine-d$_{5}$ with E$_{rel}$=2990 cm$^{-1}$ which is near $\Delta $H$_{rxn}$=3050 cm$^{-1}$. The D-atom abstraction rates are enhanced by a factor of 200-300 when the pyridine reactant is vibrationally excited. Energy measurements of the products show that the pyridinyl radical has lost only one quantum of the C-D stretch. We find that the reaction mechanism is direct with a linear transition state. The lack of energy equilibration among the reaction products highlights the local nature of the transition state and shows that most of the pyridine vibrational energy is not available to the reaction. The experimental results are compared to phase space theory calculations that predict a vibrational enhancement of $\sim $10$^{6}$-10$^{8}$. [Preview Abstract] |
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