SELECTIVE CLEAVAGE OF THE NITRO-GROUP FROM A NITROPHENYL MONOLAYER BYSYNCHROTRON SOFT-X-RAY

A synchrotron radiation source was utilized for X-ray photoelectron sp ectroscopic analysis of a nitrobenzaldimine-formed monolayer. The N(1s ) peak intensity for the nitro group becomes reduced upon X-ray irradi ation, while C(1s) and O(1s) peaks are invariant. This observation ind icates that the nitro group is cleaved selectively, leaving the phenyl ring intact in the layer. The cleavage rate is measured as a function of photon energy and normalized with the photon flux. The cleavage is first-order to the concentration of the nitro group. The rate constan t is independent of the incident photon energy, suggesting that the cl eavage is not associated with a direct photoexcitation of atomic core electrons. Electrons ejected by the X-ray are proposed as the most via ble cause for the bond cleavage. The molecules remaining on the irradi ated surface were analyzed with gas chromatography-mass spectrometry c oupled with the solid-phase microextraction method after hydrolyzing t he imine bond. It is found that the amount of nitrobenzaldehyde is red uced upon the irradiation, but the expected products, benzaldehyde and hydroxybenzaldehyde, are not produced.