Bulletin of the American Physical Society
2008 Joint Meeting of the APS Ohio-Region Section, the AAPT Southern Ohio Section, and the ACS Dayton-Section
Volume 53, Number 8
Friday–Saturday, October 10–11, 2008; Dayton, Ohio
Session A1: Plenary Session I |
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Chair: Robert Hengehold, Air Force Institute of Technology Room: Student Union E160 |
Friday, October 10, 2008 1:45PM - 2:45PM |
A1.00001: Spectroscopic indicators of life on other planets Invited Speaker: Astronomers have now identified over 300 extrasolar planets orbiting nearby stars. Most of these planets have been found by using ground-based instruments to measure Doppler shifts in the spectrum of the parent star. For stars similar to our Sun, this method is unable to find planets as small as Earth. Within the next two (three?) decades, however, NASA hopes to launch space-based telescopes that will be able to search directly for extrasolar planets. NASA's planned \textit{Terrestrial Planet Finder (TPF)} missions, will look for Earth-like planets around nearby stars and, if they exist, provide spectroscopic information on their atmospheres. \textit{TPF-C} will be a coronagraph that operates in the visible/near-IR. A variant of this idea, called \textit{TPF-O}, would replace the internal coronagraph with a free-flying occulting disk. \textit{TPF-I} is envisioned as a free-flying interferometer operating in the thermal-IR. On a planet like modern Earth, \textit{TPF-C} or \textit{TPF--O} should be able to see absorption bands of O$_{2}$, H$_{2}$O, and possibly O$_{3}$. \textit{TPF-I} would be able to see CO$_{2}$, H$_{2}$O, and O$_{3}$. Both O$_{2}$ and O$_{3}$ are considered to be good indicators of life for planets orbiting within the liquid water habitable zone of their parent star. Even better evidence for life would be the simultaneous observation of O$_{2}$ (or O$_{3})$ and a reduced gas such as CH$_{4}$ or N$_{2}$O. That may not be possible with a first-generation \textit{TPF} instrument but should ultimately be possible in the more distant future. [Preview Abstract] |
Friday, October 10, 2008 2:45PM - 3:45PM |
A1.00002: Ultrafast dynamics with laser-produced soft X-rays Invited Speaker: Laser-produced high order harmonics are used to probe chemical dynamics of atoms and molecules on femtosecond timescales. Two basic methods are developed, ultrafast transient absorption and photoelectron spectroscopy. The high order harmonics are produced with an 800 nm Ti:sapphire laser focused into a capillary or rare gas jet. Both inner shell core levels and outer shell valence states are investigated. The transient absorption of xenon ions produced by high field ionization of neutral xenon atoms is probed by core level spectroscopy. The alignment of the vacancy created in forming the ion is measured as a function of pump-probe delay by promotion of an inner d electron to the vacancy in the outer shell. Small molecules are excited to repulsive dissociative states and individual harmonics are used to obtain time-resolved photoelectron spectra. A wave packet on the dissociative state of bromine molecules is detected, as well as the production of atoms at longer time delays. By the use of velocity map imaging, the angular distributions of outgoing photoelectrons are analyzed for selected excited states of He atoms, providing new information about the relative phases and matrix elements for photoionization into the outgoing d and s waves. [Preview Abstract] |
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