Abstract
Chemisorbed films of octadecyltrichlorosilane (OTS) and ethyltrichlorosilane (ETS) at the interface calcium fluoride:air have been studied by vibrationally resonant IR pump IR-vis probe sum-frequency (SF) spectroscopy. Using a total internal reflection geometry, a signal enhancement of more than two orders of magnitude compared to the conventional setup is achieved. This enhancement in combination with two independently continously tunable infrared sources provide new insight in intramolecular energy flow processes and the corresponding relaxation times on dielectric surfaces. A fast energy exchange between the CH3-stretching modes detected by SF spectroscopy occurs within a few picoseconds. A two-exponential decay of the CH3-stretching modes is observed: The energy relaxation is fast with time constants in the picosecond range, while the ground state is repopulated in approximately 100 ps. Due to the fast energy exchange within the CH-stretching vibrations and their strong anharmonic coupling, bleaching of a SF-active mode can be achieved, even if the pumped mode does not directly contribute to the SF spectrum. This weakening of the selection rules in IR pump IR-vis probe SF spectroscopy is demonstrated for the methylene stretching vibrations of OTS.
| Original language | English |
|---|---|
| Pages (from-to) | 96-107 |
| Number of pages | 12 |
| Journal | Proceedings of SPIE - The International Society for Optical Engineering |
| Volume | 3683 |
| State | Published - 1999 |
| Event | Proceedings of the 1998 Laser Optics '98: Solid State Lasers - St. Petersburg, RUS Duration: 22 Jun 1998 → 26 Jun 1998 |