Desorption photon energy dependence

Table 4 Photon energy dependence of NO and O desorption from Pt(l 1 l)-NO, and CO and CO+ desorption from Pt(l 1 l)-CO.

Table 3 Photon energy (fio) dependence of mean translational (Tt), rotational (Tr), and vibrational (Tv) temperatures in NO and CO desorption from Pt(l 1 1) at 80 K in v = 0.

Figure A3.10.8 Depiction of etching on a Si(lOO) surface, (a) A surface exposed to Br2 as well as electrons, ions and photons. Following etching, the surface either becomes highly anisotropic with deep etch pits (b), or more regular (c), depending on the relative desorption energies for different surface sites [28].

The energies of the desorbing methyl radicals were independent of the photon flux. Desorption via local heating would be expected to show some dependence. 

Matrix-assisted iaser desorption/ionization (MALDI). This is another ionization method for the analysis of large molecules such as peptides, proteins, and nucleic acids, as well as some synthetic polymers. In MALDI, the analyte is first cocrystallized with an excess of a matrix, e.g., sinapinic acid or dihydroxybenzoic acid, that has a constituent aromatic component able to absorb photons from a UV laser beam. When the dried analyte matrix mixture is exposed (inside the vacuum chamber) to a sudden input of energy from a laser pulse the matrix evaporates, essentially instantaneously, carrying with it the analyte molecules. The matrix forms reagent ions that protonate the analytes. The selection of the matrix is critical as different compound classes exhibit substantial, matrix-dependent differences in ionization efficiency. The MALDI matrix should not be confused with the alternative use of the term matrix that is used to denote the medium in which biological and/or environmental components are presented, e.g., blood plasma, urine, sediment. 

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