An electrospray/quadrupole ion trap (QIT)/time-of-flight tandem mass spectrometer is used to study the photodissociation of gas-phase cations. The ions are formed in the electrospray source, trapped in the quadrupole, and irradiated with an argon ion laser. A time-of-flight spectrometer affords multiplex detection of all product and remaining reactant ions giving us the ability to determine reaction efficiency. The 514 nm laser beam passes through the ring electrode of the quadrupole ion trap perpendicular to the axis of the ion beam. The reactant ions can be mass isolated in the trap by supplemental AC frequencies added to one endcap of the QIT. Reactant ions are collisionally cooled for varying amounts of time in order to optimize the effects of the laser. QIT fill rates are quantified by the addition of an ion gate to the instrument, and irradiation times are varied independently of other parameters using a beam shutter placed in the path of the CW laser beam. Initial results suggest a way to determine the rate of collisional cooling inside the QIT and give insights on the dimensions of the trapped ion cloud. Evidence indicating that the interaction time with the laser, laser intensity, and buffer gas pressure inside the trap all affect the rates of dissociation will also be presented. Mechanisms for the initial photodissociation reactions will be proposed.