Berlin 2001 – scientific programme
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MO: Molekülphysik
MO 10: Spectroscopy I: Ultra-short Time Spectroscopy
MO 10.7: Talk
Thursday, April 5, 2001, 17:15–17:30, H1058
THz Time-Domain Spectroscopy on Ammonia — •Hermann Harde1, Jianxin Zhao1, Marcus Wolff2, Alan Cheville2, and Daniel Grischkowsky2 — 1Universität der Bundeswehr Hamburg, Lasertechnik und Werkstoffkunde, Germany — 2School of Electrical and Computer Engineering, Oklahoma State University, USA
We use the technique of terahertz time-domain spectroscopy to
experimentally and theoretically study the absorption and dispersion of
ammonia vapor. Our measurements show small deviations from the
rotation-inversion spectrum which originate from transitions in the ν2
hot band and from the (NH3)2 dimer. We investigate the molecular
tunneling in ammonia and apply our new molecular response theory1 to
analyze the inversion spectrum of this molecule. The theory includes the
molecular response of polar molecules to an external electric field over
the duration of a collision with the molecular response time as a control
parameter, and it unifies the basic collision theories of Lorentz, van
Vleck-Weisskopf and Debye. The calculated absorption and dispersion based
on this theory fits the measurements over the full spectral range of the
THz spectrum and allows to determine a response time of the order of 100
fs.
1. H. Harde, R. A. Cheville, D. Grischkowsky, J. Phys.
Chem. A
101, 3646-3660 (1997)