Back to Search
Start Over
Subpicosecond transient infrared spectroscopy of adsorbates. Vibrational dynamics of CO/Pt(111).
- Source :
-
Journal of Chemical Physics . 10/1/1991, Vol. 95 Issue 7, p5403. 16p. - Publication Year :
- 1991
-
Abstract
- The vibrational dynamics of excited CO layers on Pt(111) were studied using infrared (IR) pump–probe methods. Resonant IR pulses of 0.7 ps duration strongly pumped the absorption line (ν≊2106 cm-1 ) of top-site CO. Weak probe pulses delayed a time tD after the pump were reflected from the CO-covered Pt(111) surface, and dispersed in a monochromator to determine the absorption spectrum of the vibrationally excited CO band, with time resolution <1 ps and monochromator resolution <1 cm-1. Transient spectra were obtained as a function of CO coverage, surface temperature, and laser fluence. Complex spectra for tD<0 show features characteristic of a perturbed free induction decay, which are expected based on multiple-level density-matrix models. For tD≥0, the CO/Pt absorption exhibits a shift to lower frequency and an asymmetric broadening which are strongly dependent on fluence (1.3–15 mJ/cm2 ). Spectra return to equilibrium (unexcited) values within a few picoseconds. These transient spectral shifts and the time scale for relaxation do not depend (within experimental error) on coverage for 0.1≤ΘCO≤0.5 ML or on temperature for 150≤Ts≤300 K. A model for coupled anharmonic oscillators qualitatively explains the tD>0 spectra in terms of a population-dependent decrease in frequency of the one-phonon band, as opposed to a transition involving a true CO(v=2) two-phonon bound state. The rapid relaxation time and its insensitivity to Ts and ΘCO are consistent with electron–hole pair generation as the dominant decay mechanism. [ABSTRACT FROM AUTHOR]
- Subjects :
- *MOLECULAR dynamics
*VIBRATIONAL spectra
*ABSORPTION
*PHONONS
Subjects
Details
- Language :
- English
- ISSN :
- 00219606
- Volume :
- 95
- Issue :
- 7
- Database :
- Academic Search Index
- Journal :
- Journal of Chemical Physics
- Publication Type :
- Academic Journal
- Accession number :
- 7648362
- Full Text :
- https://doi.org/10.1063/1.461657