The adsorption and photochemistry of CD3I on TiO 2(110)

Simon J. Garrett, Victor P. Holbert, Peter C Stair, Eric Weitz

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

The adsorption and photochemistry of CD3I adsorbed on TiO 2(110) at ∼110 K has been studied by means of temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). Complex desorption behavior is observed in TPD suggesting the presence of several distinct coverage regimes. At submonolayer coverages there are two coexisting phases: one dominated by adsorbate-adsorbate interaction, the other dominated by adsorbate-substrate interactions. The first completed monolayer corresponds to (3.8±0.3)×1014 molecules cm-2 and shows only one desorption peak, although this is broad and extends asymmetrically to high temperature indicative of a changing desorption activation energy. With increasing coverage, a discrete, less tightly bound second layer is formed which slowly rearranges to produce three-dimensional clusters of methyl iodide, as indicated by a sharp reduction in the I (3d5/2)/Ti(2p) XPS intensity ratio. There is evidence that this rearrangement does not involve the first monolayer. Irradiation of 1 ML CD3I by 254 or 334 nm photons causes cleavage of the C-I bond and expulsion of I and C containing species into the vacuum. There is retention of ∼20% of the initial I atoms after irradiation at 254 nm. The photodissociation cross section, σ, of adsorbed CD 3 I on TiO2(110) at 254 and 334 nm is calculated to be ∼1.1×10-18 cm2 and ∼1.3 × 10 -20 cm2, respectively. At 254 nm, the adsorbate and gas phase σ are similar suggesting photodissociation is dominated by adsorbate excitation, but at 334 nm the adsorbate photodissociation cross section is almost an order of magnitude larger than its gas phase counterpart. This suggests that a second photoexcitation mechanism may be contributing to adsorbate photodissociation, possibly involving photogenerated substrate carriers.

Original languageEnglish
Pages (from-to)4615-4625
Number of pages11
JournalJournal of Chemical Physics
Volume100
Issue number6
Publication statusPublished - 1994

Fingerprint

Photochemical reactions
Adsorbates
photochemical reactions
Photodissociation
desorption
photodissociation
Adsorption
adsorption
x ray spectroscopy
Desorption
Temperature programmed desorption
Photoelectron spectroscopy
photoelectron spectroscopy
vapor phases
Monolayers
irradiation
expulsion
cross sections
Gases
Irradiation

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Garrett, S. J., Holbert, V. P., Stair, P. C., & Weitz, E. (1994). The adsorption and photochemistry of CD3I on TiO 2(110). Journal of Chemical Physics, 100(6), 4615-4625.

The adsorption and photochemistry of CD3I on TiO 2(110). / Garrett, Simon J.; Holbert, Victor P.; Stair, Peter C; Weitz, Eric.

In: Journal of Chemical Physics, Vol. 100, No. 6, 1994, p. 4615-4625.

Research output: Contribution to journalArticle

Garrett, SJ, Holbert, VP, Stair, PC & Weitz, E 1994, 'The adsorption and photochemistry of CD3I on TiO 2(110)', Journal of Chemical Physics, vol. 100, no. 6, pp. 4615-4625.
Garrett, Simon J. ; Holbert, Victor P. ; Stair, Peter C ; Weitz, Eric. / The adsorption and photochemistry of CD3I on TiO 2(110). In: Journal of Chemical Physics. 1994 ; Vol. 100, No. 6. pp. 4615-4625.
@article{b3b13527adbf4f148184bca8539a0fcd,
title = "The adsorption and photochemistry of CD3I on TiO 2(110)",
abstract = "The adsorption and photochemistry of CD3I adsorbed on TiO 2(110) at ∼110 K has been studied by means of temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). Complex desorption behavior is observed in TPD suggesting the presence of several distinct coverage regimes. At submonolayer coverages there are two coexisting phases: one dominated by adsorbate-adsorbate interaction, the other dominated by adsorbate-substrate interactions. The first completed monolayer corresponds to (3.8±0.3)×1014 molecules cm-2 and shows only one desorption peak, although this is broad and extends asymmetrically to high temperature indicative of a changing desorption activation energy. With increasing coverage, a discrete, less tightly bound second layer is formed which slowly rearranges to produce three-dimensional clusters of methyl iodide, as indicated by a sharp reduction in the I (3d5/2)/Ti(2p) XPS intensity ratio. There is evidence that this rearrangement does not involve the first monolayer. Irradiation of 1 ML CD3I by 254 or 334 nm photons causes cleavage of the C-I bond and expulsion of I and C containing species into the vacuum. There is retention of ∼20{\%} of the initial I atoms after irradiation at 254 nm. The photodissociation cross section, σ, of adsorbed CD 3 I on TiO2(110) at 254 and 334 nm is calculated to be ∼1.1×10-18 cm2 and ∼1.3 × 10 -20 cm2, respectively. At 254 nm, the adsorbate and gas phase σ are similar suggesting photodissociation is dominated by adsorbate excitation, but at 334 nm the adsorbate photodissociation cross section is almost an order of magnitude larger than its gas phase counterpart. This suggests that a second photoexcitation mechanism may be contributing to adsorbate photodissociation, possibly involving photogenerated substrate carriers.",
author = "Garrett, {Simon J.} and Holbert, {Victor P.} and Stair, {Peter C} and Eric Weitz",
year = "1994",
language = "English",
volume = "100",
pages = "4615--4625",
journal = "Journal of Chemical Physics",
issn = "0021-9606",
publisher = "American Institute of Physics Publising LLC",
number = "6",

}

TY - JOUR

T1 - The adsorption and photochemistry of CD3I on TiO 2(110)

AU - Garrett, Simon J.

AU - Holbert, Victor P.

AU - Stair, Peter C

AU - Weitz, Eric

PY - 1994

Y1 - 1994

N2 - The adsorption and photochemistry of CD3I adsorbed on TiO 2(110) at ∼110 K has been studied by means of temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). Complex desorption behavior is observed in TPD suggesting the presence of several distinct coverage regimes. At submonolayer coverages there are two coexisting phases: one dominated by adsorbate-adsorbate interaction, the other dominated by adsorbate-substrate interactions. The first completed monolayer corresponds to (3.8±0.3)×1014 molecules cm-2 and shows only one desorption peak, although this is broad and extends asymmetrically to high temperature indicative of a changing desorption activation energy. With increasing coverage, a discrete, less tightly bound second layer is formed which slowly rearranges to produce three-dimensional clusters of methyl iodide, as indicated by a sharp reduction in the I (3d5/2)/Ti(2p) XPS intensity ratio. There is evidence that this rearrangement does not involve the first monolayer. Irradiation of 1 ML CD3I by 254 or 334 nm photons causes cleavage of the C-I bond and expulsion of I and C containing species into the vacuum. There is retention of ∼20% of the initial I atoms after irradiation at 254 nm. The photodissociation cross section, σ, of adsorbed CD 3 I on TiO2(110) at 254 and 334 nm is calculated to be ∼1.1×10-18 cm2 and ∼1.3 × 10 -20 cm2, respectively. At 254 nm, the adsorbate and gas phase σ are similar suggesting photodissociation is dominated by adsorbate excitation, but at 334 nm the adsorbate photodissociation cross section is almost an order of magnitude larger than its gas phase counterpart. This suggests that a second photoexcitation mechanism may be contributing to adsorbate photodissociation, possibly involving photogenerated substrate carriers.

AB - The adsorption and photochemistry of CD3I adsorbed on TiO 2(110) at ∼110 K has been studied by means of temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). Complex desorption behavior is observed in TPD suggesting the presence of several distinct coverage regimes. At submonolayer coverages there are two coexisting phases: one dominated by adsorbate-adsorbate interaction, the other dominated by adsorbate-substrate interactions. The first completed monolayer corresponds to (3.8±0.3)×1014 molecules cm-2 and shows only one desorption peak, although this is broad and extends asymmetrically to high temperature indicative of a changing desorption activation energy. With increasing coverage, a discrete, less tightly bound second layer is formed which slowly rearranges to produce three-dimensional clusters of methyl iodide, as indicated by a sharp reduction in the I (3d5/2)/Ti(2p) XPS intensity ratio. There is evidence that this rearrangement does not involve the first monolayer. Irradiation of 1 ML CD3I by 254 or 334 nm photons causes cleavage of the C-I bond and expulsion of I and C containing species into the vacuum. There is retention of ∼20% of the initial I atoms after irradiation at 254 nm. The photodissociation cross section, σ, of adsorbed CD 3 I on TiO2(110) at 254 and 334 nm is calculated to be ∼1.1×10-18 cm2 and ∼1.3 × 10 -20 cm2, respectively. At 254 nm, the adsorbate and gas phase σ are similar suggesting photodissociation is dominated by adsorbate excitation, but at 334 nm the adsorbate photodissociation cross section is almost an order of magnitude larger than its gas phase counterpart. This suggests that a second photoexcitation mechanism may be contributing to adsorbate photodissociation, possibly involving photogenerated substrate carriers.

UR - http://www.scopus.com/inward/record.url?scp=0000811036&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0000811036&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0000811036

VL - 100

SP - 4615

EP - 4625

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 6

ER -