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Carbon Disulfide Dissociation in a Thermal Cell' Try C. Peng McDonnell Douglas Research Laboratories, McDonneil Douglas Corporation, St. Louis, Missouri 63766 (Received June 13, 1974; Revised Manuscript Received October 18, 1973) Publication costs assisted by the McDonneil Douglas Corporation
Dissociation products of CS2 in a vitreous carbon thermal cell are analyzed mass spectrometrically for temperatures up to 1900 K. The reaction products in the cell are observed directly through an effusive flow with a modulated beam sampling technique. CS and S are the only detected products from CS2 dissociation, indicating CS2 CS + S is the dominant reaction. The temperature variation of the relative CS and S abundances indicates that CS2 Cwall 2CS is also a significant reaction in the CS2 dissociation. The measured relative abundances of CS2 and CS as a function of temperature agree favorably with those of the equilibrium calculations using the recently obtained C S heat of formation (AHfOo = 69.2 kcal/mol a t 0 K). On the other hand, the absence of Sp in our measurements is in support of the CS2 reaction with the heated vitreous carbon wall mentioned previously. -+
Introduction Dissociation of CS2 yields C S molecules which are important intermediates in CS2-0 CO chemical lasersS2The chemistry of CS2 dissociation has been observed under a high-frequency discharge at 1 Torr,3 by flash photolysis at 100 Torr,4 by shock wave heating a CS2-Ar mixture from 2000 to 3500 K at 1-10 T0rr,~,6and by passing CS2 over a heated tungsten ribbon.? The high-frequency discharge and flash photolysis studies as well as ac discharge studies8 concentrated on the generation and lifetime of the CS molecule. C S was also observed in interstellar space,g therefore by itself a CS molecule appears stable. The shock wave heating studies produced information on the CS2 decomposition rate, and the heated tungsten ribbon studies suggest a potential mechanism for CS2 dissociation. However, the details of the mechanism are not completely understood. This paper present a mass spectrometric analysis of CS2 dissociation products in a vitreous carbon thermal cell together with new experimental evidence for specific dissociation reactions. The Journal of Physical Chemistry, Voi. 78, No. 6, 1974
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Experimental Section The experimental arrangement is shown in Figure 1. Major components are (1) the vitreous carbon thermal cell, (2) the beam modulating system-the vibrating fork (Bulova, L-40-P) and the lock-in amplifier (PAR, HR-8), (3) the quadrupole mass spectrometer (EA1 Quad 150A), and (4) the vacuum chamber (60 cm diameter and 90 cm long) together with a diffusion pump system. The vitreous carbon thermal cell (17.4 mm diameter 25.4 mm long cylinder) is a high-temperature oven specially fabricated for material-environmental research. The design and performance of this thermal cell has been reported elsewhere.1° For CS2 dissociation studies, a steady flow of 30% CS270% Ar (mole ratio) gas mixture was maintained through the vitreous carbon thermal cell. The input of this flow was at the water-cooled copper electrodes (Figure 1).The input flow rate was controlled by a variable leak (Granville-Phillip series 203) and was measured to be 2.4 x 10-6 g/sec by a mass flow meter (Hasting, ALL-10). The output of this steady flow was through three pin holes
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CS2 Dissociation in a Thermal Cell
Vacuum chamber with pressure 5 x l 0-5 Torr
