Abstract
A mass spectrometer has been coupled to an open‐tube, vapor‐phase, crystal growth apparatus in order to study vapor‐phase processes leading to the deposition of 
crystals. Studies of the 
and Cl2 reactions with gallium showed that 
is the only gallium chloride formed. Studies of 
decomposition showed that very little 
decomposes under given experimental conditions, but this can be changed by the presence of W and Pt. Thermochemical data were collected or calculated for all species detected in the system. The reaction mechanisms leading to the deposition of 
are discussed. It is concluded that the reaction controlling the deposition of 
can be written as
Comparison of the experimentally determined vapor composition with one predicted from the available thermochemical data showed that important deviations from the thermochemical equilibrium occur in our system.