THE 248-NM EXCIMER-LASER-ABLATION MECHANISM OF LIQUID BENZENE-DERIVATIVES - PHOTOCHEMICAL FORMATION OF BENZYL RADICAL LEADS TO ABLATION

The mechanism underlying 248-nm laser ablation of liquid benzene deriv atives (alkyl benzenes, benzyl chloride, benzyl alcohol) was revealed by means of transient absorption spectroscopy. One characteristic in t he present liquid system is that the ablation threshold can be correla ted not to the boiling point at all but to the photochemical reactivit y of beta-bond cleavage. In the spectroscopic measurement, the benzyl- radical formation was confirmed upon ablation, and its Concentration w as quantitatively evaluated at the threshold. The obtained value was s imilar to 0.05 M, which was almost common to all of the examined Liqui ds. The result means that the present liquids, whose macroscopic physi cal properties such as surface tension do not differ too much from eac h other because of the analogous molecular structure, undergo the abla tion when the radical concentration reaches the critical value of 0.05 M. This is the first demonstration for bridging a gap between microsc opic photochemical process and macroscopic morphological change. The a blation behavior can be well interpreted in terms of the photochemical volume explosion.