Editing Desorption (section)

===IR photodesorption===
IR photodesorption is a type of desorption that occurs when an infrared light hits a surface and activates processes involving the excitation of an internal vibrational mode of the previously absorbed molecules followed by the desorption of the species into the gas phase.<ref name="Hussla">PHYSICAL REVIEW 8, volume 32, number 615. September 1985. Infrared-laser-induced photodesorption of NH3 and ND3 adsorbed single crystal Cu(100) and Ag film. IngoHussla, H.Seki, T.J.Chuang. IBMResearchLaboratory, SanJose, California.</ref> One can selectively excite electrons or vibrations of the adsorbate or of the adsorbate-substrate coupled system. This relaxation of the bonds together with a sufficient energy exchange from the incident light to the system will eventually lead to desorption.<ref name="Brivio">Surface Science Reports 17 (1993) 1-84 North-Holland. Dynamics of adsorption/desorption at solid surfaces G.P. Brivio a and T.B. Grimley b,1 Dipartimento di Fisica dell'Universith di Milano, Via Celoria 16, 20133 Milano, Italy h The Donnan Laboratories, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK Manuscript received in final form 25 August 1992  </ref> 

Generally, the phenomenon is more effective for weaker-bound physisorbed species, which have a smaller adsorption potential depth compared to that of the chemisorbed ones. In fact, a shallower potential requires lower laser intensities to set a molecule free from the surface and make IR-photodesorption experiments feasible, because the measured desorption times are usually longer than the inverse of the other relaxation rates in the problem.<ref name="Brivio" />