Synchronized flash photolysis and pulse deposition in matrix isolation experiments

An apparatus is described which permits flash photolysis of a pulse-deposited gas mixture in a matrix isolation experiment. This technique obviates the limitations of in situ photolysis imposed by the cage effect and by secondary photolysis. The matrix is deposited in pulses at 30-s intervals and photolyzed sequentially by four synchronized flashlamps approximately 1 ms before the pulse strikes the cold surface. Pulsed deposition maintains adequate isolation and causes line narrowing, which enhances spectral sensitivity. The efficacy of flash photolysis combined with pulsed deposition for producing and trapping transient species was demonstrated by infrared detection of CF₃ (from photolysis of CF₃I/Ar mixtures) and of ClCO (from photolysis of Cl₂/CO/Ar mixtures). The apparatus was used to study the photolytic decomposition of gaseous tricarbonylironcyclobutadiene, C₄H₄Fe(CO)₃. The results indicate that the primary photolytic step is not elimination of C₄H₄, as suggested earlier, but rather of CO.