A cw CO.sub.2 tunable laser is employed to irradiate an allyl halide selected from allyl chloride, allyl bromide, allyl fluoride, 2-methyl-3-chloropropene, and 2,3-dichloropropene and contained in one or more reaction cells at a predetermined pressure. A predetermined power level from about 25 to 150 watts, an irradiating time from about 0.2 second to about 60 seconds, and a selected radiation line for example P(36), P(32), P(28), P(26), or P(22) (that is resonant with an absorption band of the selected allyl halide) are employed to achieve dissociation of the selected allyl halide and to achieve a laser-induced photochemical synthesis of benzene and substituted benzenes.