No abstract

An experimental setup that coupled IR multiple‐photon dissociation (IRMPD) and laser‐induced fluorescence (LIF) techniques was implemented to study the kinetics of the recombination reaction of dichlorocarbene radicals, CCl2, in an Ar bath. The CCl2 radicals were generated by IRMPD of CDCl3. The time dependence of the CCl2 radicals’ concentration in the presence of Ar was determined by LIF. The experimental conditions achieved allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C2Cl4. The rate constant for this reaction was determined in both the falloff and the high‐pressure regimes at room temperature. The values obtained were k0 = (2.23 ± 0.89) × 10−29 cm6 molecules−2 s−1 and k∞ = (6.73 ± 0.23) × 10−13 cm3 molecules−1 s−1, respectively.

An intracavity system for the infrared multiple photon dissociation (IRMPD) of molecules with high dissociation energy threshold has been designed and implemented. The system design based on a TEA CO 2 laser with a cavity folded in V-shape included the analysis of its stability varying the cavity dimensions as well as the analysis of the positions of the beam waists and of the beam size at them. The intracavity energy as a function of the total sample pressure has been measured and the laser-operation threshold has been determined. Intracavity IRMPD has been compared to traditional IRMPD performed in an irradiation geometry in which the radiation is focused into a photoreactor placed outside the laser cavity. Dissociation volumes in intracavity irradiation have resulted an order of magnitude larger than those obtained in experiments performed with the photoreactor outside the laser cavity.

The infrared multiphoton dissociation (IRMPD) of CDCl3 in the presence of O2 and NO2 as acceptor gases has been studied. We have worked with both pure CDCl3 and mixtures with CHCl3. The reaction mechanism following IRMPD of CDCl3 is discussed in detail. CCl2O, CCl4 and DCl were found to be the main products. With added O2, the observed CDCl3 dissociation was larger than with nonoxygenated acceptor gases. The reaction mechanism probably involves a catalytic cycle initiated by the oxidation of CCl3. With the aim of discriminating the different CDCl3 dissociation mechanisms, the IRMPD of CDCl3 in the presence of NO2 was first studied. In order to make evident the CDCl3 dissociation produced by the catalytic cycle, we then studied the IRMPD of CDCl3 in mixtures with CHCl3 with O2 as the acceptor gas. In this case, the dissociation mechanism subsequent to IRMPD is evidenced in the competence between the two isotopic species.