Table 2. Lifetimes of the shortest-lived neutral species calculated by PumpKin for 5 slm He flow and 14 W cm^–3 plasma power, and varying humidity content. Conditions are the same as for the investigations of OH densities under a variation of the humidity content discussed later in Section 4.2. These lifetimes serve as timescale of interest for the pathway analysis.

H2O content (ppm)	He* lifetime (μs)	He2* lifetime (μs)
10	2.539	1.931
100	0.350	0.188
1000	0.036	0.021
10 000	0.004	0.013