Thickness effects of water overlayer on its explosive evaporation at heated metal surfaces

Molecular dynamics (MD) simulations have been employed to investigate the e ffect of the thickness of a water overlayer on the character of its ejectio n from a heated Au surface. The simulations are performed for five systems differing in the thickness of the water overlayer which was adsorbed on a m etal substrate heated to 1000 K. For each system, an explosive evaporation occurs in the part of the water film adjacent to the metal surface and the upper part of the film is pushed off by the generated force. The average ma ximum temperature of the water film decreases as the film thickness increas es. In contrast, the temperature achieved by the fast cooling due to the ex plosive evaporation shows an inverse trend. The significance of these model calculations to matrix-assisted laser desorption and ionization (MALDI) ma ss spectrometry is discussed. (C) 2001 Elsevier Science B.V. All rights res erved.