Developments in Inorganic Arc Plasma Chemistry

Abstract

indicate a strong preference for the formation of hydrogen fluoride with) = 2. Accordingly transitions from v --2 to v = 1 also occur preferentially in lasers pumped by reaction (1). This emission appears in the infrared region between 2.7 and 2.9pm. In laser systems in which the additional reaction (6) contributes to the pumping, higher vibrational states up to v = 6 are excited. The emission at about 3 pm corresponds to a large number of vibrational-rotational lines, but n o detailed rate constants have been published so far 15,141. This description of the parameters of chemical laser emission has been confined to hydrogen fluoride lasers as the area that has been most extensively studied. In view of the intense activity in this field, however, similar results may be expected in the near future for other, new chemical lasers. Possible ApplicationsThere is considerable scope for the use of these lasers in various fields. In chemistry, sources of strong monochromatic infrared radiation offer the longterm prospect of use as a "selective Bunsen burner" with the object of carrying out chemical reactions with a controlled supply of energy in certain vibra- (preparation e.g. of compounds containing nitrogen, C-N and C-F compounds, ozone, nitrides, cyanides, carbides, metal oxides, and metals from metal oxides and from halides). Development and Present Position of Plasma ChemistryA plasma is nowadays generally taken to be a partly or completely ionized gas that is externally electrically neutral, conducts electricity, and has a higher internal energy than an un-ionized gas. The energy required for the production and maintenance of a plasma can [*I Dr. U. Landt Knapsack AG 5033 Knapsack bei Koln (Germany) be supplied as heat or as electrical or mechanical energy. The most important methods for the supply of electrical energy are arc and glow discharges and electrodeless discharges (high frequency and microwave discharges). Only the arc plasma and its use will be discussed here.The term "plasma chemistry" is at present used only reluctantly in the literature. Since chemical bonds d o not exist at the high temperatures characteristic of most types of plasma, the term is really self-contradictory. Nevertheless, it is shorter than any of the 780 Angew. Chem. internat. Edit. 1 Vol. 9 (1970) 1 No. 10 alternatives, and will therefore be used here in the sense of the performance of chemical reactions in o r with the aid of plasmas.Chemical plasma processes have been known since the industrial production of oxides of nitrogen by "combustion of air" in the flame arc furnace (Birkeland and Eyde; Schonherr and Pauling). The development of plasma chemistry stopped for a long time after the replacement of this process by the cheaper combustion of ammonia. This standstill was mainly due to the high cost of electricity and technical problems.For some 10 to 7 5 years, however, plasma chemistry has been developing rapidly, at least on the research side. The intense activity in high-temperature physics in connection with nuclear fu...