The process of heat release during carbon particle formation and growth after pyrolysis of carbon suboxide C3O2 behind shock waves was investigated. For this goal, temp. and optical d. of gas-particle mixts. initially consisting of 3% C3O2 + 5% CO2 in Ar were measured as a function of time. The temp. was detd. by two-channel emission-absorption spectroscopy at l = 2.7 +- 0.4 micro m, corresponding to the CO2 (1,0,1) vibrational band. In the range of initial temps. behind the shock waves from 1600 up to 2200 K a significant heating of the mixt. during particle formation and growth was obsd. that increased towards higher temps. The anal. of the obtained data in combination with previous results about the temp. dependence of the particle size shows a decrease of the heat release of condensation from.apprx.200 kJ/mol per atom for particles contg.apprx.1000 atoms to.apprx.50 kJ/mol per atom for particle contg.apprx.106 atoms.