Excimer laser photolysis, experimental

Figure 4.2. Experimental set-up for kinetic studies of SiHj reactions by excimer laser photolysis in a tubular slow-flow reactor with time-resolved detection by molecular beam sampling, near-threshold ionization electron impact mass spectrometry...

As has been shown in various experimental studies the excimer laser photolysis/ laser long path absorption/cw LIF technique developed in our laboratory within the LACTOZ program provides reliable information on branching ratios and rate coefficients in hydrocarbon oxidation under simulated NOx rich tropospheric conditions. As an systematic extension of our previous work on the alkane series Cl - Ce in the present period it was aimed to study ... 

The oxidation of the hydrocarbons has been studied by observing the temporal evolution of OH and NO2 following the pulse initiation of the oxidation chain using Cl atoms generated via excimer laser photolysis of CI2 at / = 351 nm. A detailed description of the experimental technique can be found elsewhere [1] and is not repeated here. 

Until quite recently, direct measurements of o(>d2)(X) were limited by the very real experimental difficulties associated with the highly efficient deactivation of O ( D2) by O3, as well as the need to provide a sensitive probe for atomic oxygen atoms in the ground Pj state as well as in the electronically excited D2 state. The development of resonance spectroscopic techniques for time-resolved detection of O ( Pi) has permitted monitoring of this state at densities of ca. 10 cm with an instrumental bandwidth in excess of 10 MHz. When combined with the use of high intensity photolysis sources such as the excimer lasers and frequency quadrupled Nd/YAG, it has proved possible to measure directly the yield of 0( D2) and O( Pj) at several discrete wavelengths in the middle ultraviolet. 

The only method that allowed the matrix isolation of lb so far is the vacuum UV photolysis of difluoroacetylene 6. [33] Difluoroacetylene 6 exhibits a UV absorption with a maximum < 200 nm that shows a tailing to 250 ran. Irradiation of matrix-isolated 6 with the 193 nm light of an ArF excimer laser produces a new species in high yields that was identified as vinylidene lb. All fundamental IR vibrations of lb were observed experimentally, and band positions and relative intensities could be nicely reproduced by DFT and ab-initio calculations. 

Figure 14. Schematic diagram of the CO metastable TOF experimental apparatus is shown. The molecular beam (MB) containing 10% ketene in neon or helium can be placed at any acute angle (0,ab) relative to the flight path, and it is collimated by an electroformed skimmer (not shown). The photolysis laser is an unpolarized excimer (XeCl or XeF), and the probe laser is a pulse dye amplification system whose polarization can be made either parallel (sPR, ) or perpendicular (e ) to the flight path. The metastables pass through a 1-cm orifice and deflector plates and grids (both not shown), and they strike a heated Ni surface. Electrons produced from the Ni surface by the metastables are steered by a plate set at —1500 V onto a stack of 3 MCPs the resulting pulses are then amplified, discriminated against noise from dark current, and counted by a multichannel scaler.

---