IR-LASER INDUCED BRANCH CHAIN REACTION OF HYPOFLUORITES WITH HYDROGEN

The parameters of chain explosion occurrence in the mixture of CF3OF or CFz(OF)2 with hydrogen induced by a pulsed CO2-1aser were studied experimentally. The ranges of inflammation for the both cases were obtained. IR-fluorescence spectra associated with the chain explosion were studied. The chemical reactions describing the observed process qualitatively are given assuming the chain energy branching.

These substances attract attention due to their fluorination property which compares unfavourably only with that of elementary fluorine.When the mixture of CF3OF with H21 is induced with a pulsed CO2-1aser elementary fluorine is extacted which can be used to solve various problems in chemistry and quantum electronics.As paper shows the above laser-chemical reaction proceeds by the chain mechanism.During the reaction hypofluorite pressure threshold is observed, above which during laser initiation a gas explosion takes place.The explosion was detected by the variation of IR spectrum after a single pulse.The threshold pressure value is --0.6 Torr for CF3OF in its mixture with --1.8 Torr of hydrogen.
In this paper some parameters of the chain explosion occurrence for CF3OF and CF2(OF)2 as well as the parameters of IR radiation, accompanying the observed process are studied experimentally.
The gas excitation was achieved with a pulsed CO2-1aser having the pulse energy up to 10 J at pulse frequency v 931 cm -1 and pulse duration --200 ns at its half-height.The studied gas was fed into a stainless steel reactor with windows made of NaC1, CaF2, BaF2 (depending on the problem being solved) and sealed with indium and teflon.The basic component content in the initial hypofluorites was not less than 98%, F2 and COF2 being the major impurities.
The measurements of the threshold energy density of the exciting CO2-1aser were made based on the hydrogen quantity, hypofluorite pressure being 1 Torr.The chain reaction was measured from the IR absorption spectrum change after each pulse using NKC 29 spectrophotometer.The results are given in Figures 1 and 2. The chain reaction dynamics study was performed by type CF-223A photoresistor in a type C8-14 oscillograph.The circuit time resolution is --1/zs.Radiation spectra detected by type SPM-2 KBr prism monochromator are given in Figure 3 (a,b).Each spectrum contained wave bands with maximums at 2.7 m and 5.5 tm.When the component ratios of the mixture changed, the intensities of the bands having maximums at 2.7 and 5.5 m changed differently.It confirmed the fact that different compounds are responsible for the fluorescence.The wave band having maximum at 5.5 m can be related to the excited COF2 molecules.IR fluorescence spectrum of COF2 with nitrogen excited in the pulsed gas discharge can prove the fact.The spectrum was measured on the same experimental base.IR and mass spectrum analysis of the final products shows two similar products of laser- 113 LABER ENERGY, J/cm-: Figure 2 Hydrogen pressure dependence of threshold laser energy density for the chain explosion in the gas mixture CF2(OF)2 + H2 (PcF2(OF)2 Torr).
chemistry reaction: HF and COF2.We cannot expect identical intermediate radicals for these two cases.Radiation similar to that observed at 2.7/xm was obtained for the mixture SF6:Hz:F2 during IR laser excitation.According to 2 it can be interpreted as HF fluorescence.
We can conclude from the obtained experimental results that the CF3OF or CFz(OF)2 can react in the mixture with hydrogen according to the branched chain mechanism.Inflammation area 3 observed for the both hypofluorites (see Figures 1  and 2) can be regarded as a proof of the branching.
As it is well known the existence of lower inflammation threshold is related with the concurrence of chain branching rate with the chain break rate at the reactor walls.The first rate is directly proportional to the pressure, while the rate of chain break at the wall is kinetically independent of pressure, and diffusionally it increases with the pressure drop.Therefore at rather low pressures chain break rate on the wall will always limit the increase of the number of active centers in the branching reactions.
The existence of the lower threshold can be explained by the concurrence of (2) and (9).When the hydrogen pressure rises the probability of triple collisions of COF and CF3OF* rises with the energy loss.The second lower threshold can be explained by reactions (5), (7) and (9).
The addition of fluorine into the reaction mixture adds one additional reaction continuing the chain: H" + F2 HF* + F" (13) Here, as we see from the sequences (1)-(12) the increase of fluorescence intensity should take place for the both molecules.
The performed experiment at the ratio CF3OF:H2 2 Torr: 4 Torr showed that the addition of fluorine in the range of 0.2-4 Torr brings about fluorescent band intensity increase with its subsequent suppression.Here the maximum at 2.7/zm is reached at fluorine pressure of 1 Torr, and at 5.5/xm--at fluorine pressure 2.6 Torr.Fluorine prolongs fluorescence from 70/zs to about 400/zs.Fluorescent pulse delay from that of the laser pulse prolongs from zero to 300-350/zs.

Figure
Figure Figure 3 explosion.