Compact embedded device for lock-in measurements and experiment active control.

We present a multi-purpose toolkit for digital processing, acquisition, and feedback control designed for physics labs. The kit provides in a compact device the functionalities of several instruments: function generator, oscilloscope, lock-in amplifier, proportional-integral-derivative filters, ramp scan generator, and a lock-control. The design combines field-programmable-gate-array processing and microprocessor programing to get precision, ease of use, and versatility. It can be remotely operated through the network with different levels of control: from simple off-the-shelf Web graphical user interface to remote script control or in-device programmed operation. Three example applications are presented in this work on laser spectroscopy and laser locking experiments. The examples include side-fringe locking, peak locking through lock-in demodulation, and complete in-device Pound-Drever-Hall modulation and demodulation at 31.25 MHz and advanced acquisition examples like real-time data streaming for remote storage.

Rate measurement of the reaction of CF2Cl radicals with O2.

We have studied the association reaction of the CF(2)Cl radicals with O(2) in presence of N(2). The infrared multiple photon dissociation (IRMPD) technique with a homemade TEA CO(2) laser was used for the CF(2)Cl radical generation and the vibrational chemiluminiscence technique was set up for the study of the reaction kinetics. The time-resolved IR fluorescence of the vibrationally excited CF(2)O photoproduct was used to measure the disappearance rate of these radicals. A kinetic mechanism is presented to account for the rate of production of CF(2)O(*). The CF(2)Cl radical association reaction rate with O(2), evidence of a direct channel of photoproduct formation and its reaction rate, and the CF(2)O(*) collisional deactivation rate have been obtained.

Chloroform infrared multiphoton dissociation in the presence of O2 and NO2.

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.

Laser flash photolysis in a O3/Cl2 mixture at 266 nm in a very low-pressure flow system.

The laser flash photolysis in a very low-pressure flow system with mass spectrometry detection technique was developed for the study of oxidation reactions of chlorofluorocarbons. In this work, we have studied the UV photolysis of O3 in the presence of Cl2 at room temperature, which presents two catalytic cycles of O3 depletion with efficiencies dependent on the partial pressures in the photoreactor. The ozone dissociation was initiated with fourth harmonic pulses of a Nd:YAG laser. The detection of the reactants and the final and intermediate reaction products was performed with real-time mass spectrometry. The variations of the O3, Cl2 and ClO concentration were measured. The equations system associated to a proposed kinetic scheme was solved numerically and excellent agreement with the experimental results was obtained. The results from this work allowed the determination of the wall loss rates of the O(1D), Cl and ClO radicals.