High-energy H2O beams generated by a de Laval nozzle, meant for the growth of zinc oxide thin films through chemical vapor deposition, were assessed based on compressible flow theory at various divergent aperture angles. In this process, high temperature H2O was generated by a catalytic reaction between H-2 and O-2 on Pt nanoparticles and effused through the nozzle into the reaction zone. The theoretical beam temperature distributions, reduced scaling parameters and mean cluster sizes of the H2O beams generated at angles between 50 and 90 degrees were evaluated. The reduced scaling parameters of the H2O beams for all angles were calculated to be less than 200 and the mean cluster sizes were estimated to be less than one irrespective of the divergent aperture angle of the nozzle, suggesting that clusters are not formed in the H2O beam in our apparatus. The crystallinity and electrical properties of the zinc oxide films grown using various divergent aperture angles were also evaluated. (C) 2016 The Japan Society of Applied Physics