Abstract
The UV photodesorption of methyl halides from TiO2(110) has been investigated using quadrupole mass spectrometry. For low fluence irradiation (2) and ≤1 ML coverages of methyl iodide, the photodesorption yield decreases exponentially with photon dose, indicating a nonthermal, single-photon process. The wavelength and coverage dependence of the photodesorption yield and the effect of spacer layers support the conclusion that photodesorption of CH3X (X=I and Br) is initiated by substrate excitation, i.e., photogenerated electrons in the conduction band of TiO2. CH3I and CH3Br desorb from TiO2(110) on 257 nm irradiation, while CH3Cl does not photodesorb in the absence of a photoactive coadsorbate, such as CH3I. This indicates that desorption results from a resonant interaction of subvacuum-level electrons with an adsorbate electronic state. Momentum transfer from energetic photofragments to adsorbates can account for only a minor fraction of the total photodesorption yield for coverages of 1 ML or less. For high fluence irradiation (≥7 mJ/cm2), the nonlinearity of the desorption yield, the calculated transient surface temperature rise, and the desorption of an inert adsorbate (CH3OH at ≥ 12 mJ/cm2) indicate that a laser-induced thermal desorption mechanism is dominant.
| Original language | English |
|---|---|
| Pages (from-to) | 5080-5088 |
| Number of pages | 9 |
| Journal | Journal of Chemical Physics |
| Volume | 108 |
| Issue number | 12 |
| Publication status | Published - Mar 22 1998 |
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ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
Cite this
UV-induced desorption of CH3X (X=I and Br)/TiO2(110). / Kim, Seong Han; Stair, Peter C; Weitz, Eric.
In: Journal of Chemical Physics, Vol. 108, No. 12, 22.03.1998, p. 5080-5088.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - UV-induced desorption of CH3X (X=I and Br)/TiO2(110)
AU - Kim, Seong Han
AU - Stair, Peter C
AU - Weitz, Eric
PY - 1998/3/22
Y1 - 1998/3/22
N2 - The UV photodesorption of methyl halides from TiO2(110) has been investigated using quadrupole mass spectrometry. For low fluence irradiation (2) and ≤1 ML coverages of methyl iodide, the photodesorption yield decreases exponentially with photon dose, indicating a nonthermal, single-photon process. The wavelength and coverage dependence of the photodesorption yield and the effect of spacer layers support the conclusion that photodesorption of CH3X (X=I and Br) is initiated by substrate excitation, i.e., photogenerated electrons in the conduction band of TiO2. CH3I and CH3Br desorb from TiO2(110) on 257 nm irradiation, while CH3Cl does not photodesorb in the absence of a photoactive coadsorbate, such as CH3I. This indicates that desorption results from a resonant interaction of subvacuum-level electrons with an adsorbate electronic state. Momentum transfer from energetic photofragments to adsorbates can account for only a minor fraction of the total photodesorption yield for coverages of 1 ML or less. For high fluence irradiation (≥7 mJ/cm2), the nonlinearity of the desorption yield, the calculated transient surface temperature rise, and the desorption of an inert adsorbate (CH3OH at ≥ 12 mJ/cm2) indicate that a laser-induced thermal desorption mechanism is dominant.
AB - The UV photodesorption of methyl halides from TiO2(110) has been investigated using quadrupole mass spectrometry. For low fluence irradiation (2) and ≤1 ML coverages of methyl iodide, the photodesorption yield decreases exponentially with photon dose, indicating a nonthermal, single-photon process. The wavelength and coverage dependence of the photodesorption yield and the effect of spacer layers support the conclusion that photodesorption of CH3X (X=I and Br) is initiated by substrate excitation, i.e., photogenerated electrons in the conduction band of TiO2. CH3I and CH3Br desorb from TiO2(110) on 257 nm irradiation, while CH3Cl does not photodesorb in the absence of a photoactive coadsorbate, such as CH3I. This indicates that desorption results from a resonant interaction of subvacuum-level electrons with an adsorbate electronic state. Momentum transfer from energetic photofragments to adsorbates can account for only a minor fraction of the total photodesorption yield for coverages of 1 ML or less. For high fluence irradiation (≥7 mJ/cm2), the nonlinearity of the desorption yield, the calculated transient surface temperature rise, and the desorption of an inert adsorbate (CH3OH at ≥ 12 mJ/cm2) indicate that a laser-induced thermal desorption mechanism is dominant.
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M3 - Article
VL - 108
SP - 5080
EP - 5088
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 12
ER -