Photoacoustic, Photothermal Beam Deflection and Flash Photolytic- High Pressure Rate Studies Done with a Pulsed Nd:YAG Laser

A combination of photoacoustic (PA), photothermal beam deflection (PBD) and fluorimetric spectroscopic measurements has been used to determine fluorescence quantum yields for cresyl violet perchlorate in methanolic and aqueous solutions. A concentration dependence of the fluorescence quantum yield is found to be significant. The same Quanta Ray DCR-2 Nd:YAG laser used in the PA and PBD experiments has been the flash photolysis light source at λ = 355 nm for a rate study of ring closure reactions of Mo(CO)5L complexes where L is one of several substituted 2,2'-bipyridine chelating ligands. The laser pulse creates the Mo(CO)5L species from Mo(CO)6/L dissolved in toluene. The sample liquid is in a compressible quartz pill-box cell housed in a steel autoclave that can be pressurized to 200 MPa. Values of the activation parameters ΔS# and ΔV# for the rate determining ring closure reaction are small and negative for two of the 2,2'-bipyridine ligands supporting the concept of an associative interchange mechanism for CO extrusion. For another, bulkier 2,2'-bipyridine type ligand ΔV# is small and positive suggesting a dissociative interchange mechanism. These results demonstrate a changeover in reaction mechanism with changes in steric hindrance.