A theoretical consideration of chemi-ionisation of excited atoms in crossed atomic beams is made. A decrease in the effective temperature of atoms in the beam compared with the temperature of its effusive source is predicted. A critical analysis of the the rate constant measurements for associative ionisation of excited sodium (Na(3P)+Na(3P) to Na₂⁺+e) using gas cell, single atomic beam and crossed atomic beam experiments is performed. Proper considerations of the resonance radiation imprisonment in the experimental conditions are proposed.