Table 8. Neutral chemistry.

No.	Reaction (rxn)	Rate a	Ref.
Two-body collisions
312	He + O(1D) → O + He	7.0 × 10–22	145 b
313	He + O(1S) → O + He	7.0 × 10–22	As rxn 312
314	He + O2(a 1Δ) → O2 + He	8.0 × 10–27	146 b
315	He + O2(b 1Σ) → O2(a 1Δ) + He	1.0 × 10–23T00.5	125 c
316	2He* → He + He+ + e	4.5 × 10–16	46 and 97
317	2He* → He2+ + e	1.05 × 10–15	46 and 97
318	He* + He2* → 2He + He+ + e	5.0 × 10–16	97 d
319	He* + He2* → He + He2+ + e	2.0 × 10–15	97 d
320	He* + OH → OH+ + He + e	6.08 × 10–16	As rxn 321
321	He* + H2O → He + H2O+ + e	6.08 × 10–16	147 e
322	He* + H2O → He + OH+ + H + e	1.39 × 10–16	147 e
323	He* + H2O2 → He + OH+ + OH + e	6.08 × 10–16	As rxn 321
324	He* + O → O+ + He + e	2.54 × 10–16	As rxn 327
325	He* + O(1D) → O+ + He + e	2.54 × 10–16	As rxn 327
326	He* + O(1S) → O+ + He + e	2.54 × 10–16	As rxn 327
327	He* + O2 → O2+ + He + e	2.54 × 10–16	148
328	He* + O2(a 1Δ) → O2+ + He + e	2.54 × 10–16	As rxn 327
329	He* + O2(b 1Σ) → O2+ + He + e	2.54 × 10–16	As rxn 327
330	He* + O3 → O2+ + O + He + e	2.6 × 10–16	74 c
331	He2* + H2O → 2He + H2O+ + e	2.2 × 10–15	149
332	He2* + O → O+ + 2He + e	3.6 × 10–16	As rxn 335
333	He2* + O(1D) → O+ + 2He + e	3.6 × 10–16	As rxn 335
334	He2* + O(1S) → O+ + 2He + e	3.6 × 10–16	As rxn 335
335	He2* + O2 → O2+ + 2He + e	3.6 × 10–16	149
336	He2* + O2(a 1Δ) → O2+ + 2He + e	3.6 × 10–16	As rxn 335
337	He2* + O2(b 1Σ) → O2+ + 2He + e	3.6 × 10–16	As rxn 335
338	He2* + O3 → O2+ + O + 2He + e	3.6 × 10–16	74 c
339	H + HO2 → H2 + O2	5.6 × 10–18	88
340	H + HO2 → 2OH	7.2 × 10–17	88
341	H + HO2 → H2O + O	2.4 × 10–18	88
342	H + H2O2 → H2O + OH	1.7 × 10–17e–1800/Tg	150
343	H + H2O2 → H2 + HO2	2.8 × 10–18e–1890/Tg	150
344	H + O3 → OH + O2	1.4 × 10–16e–470/Tg	151 and 152
345	H2 + OH → H2O + H	4.27 × 10–19T02.41e–1240/Tg	153
346	H2 + O(1D) → OH + H	1.2 × 10–16	88
347	H2 + O(1S) → OH + H	1.2 × 10–16	As rxn 346
348	2OH → H2O + O	6.2 × 10–20T02.6e945/Tg	88
349	OH + HO2 → O2 + H2O	4.8 × 10–17e250/Tg	88, 154 and 155
350	OH + H2O2 → HO2 + H2O	2.9 × 10–18e–160/Tg	88
351	OH + O → H + O2	2.4 × 10–17e110/Tg	88, 156 and 157
352	OH + O(1D) → O2 + H	2.4 × 10–17e110/Tg	As rxn 351
353	OH + O(1S) → O2 + H	2.4 × 10–17e110/Tg	As rxn 351
354	OH + O3 → O2 + HO2	1.7 × 10–18e–940/Tg	88
355	H2O + O(1D) → 2OH	1.63 × 10–16e60/Tg	151
356	H2O + O(1S) → O + H2O	4.5 × 10–17	158
357	H2O + O(1S) → O(1D) + H2O	1.5 × 10–16	158
358	H2O + O(1S) → 2OH	3.05 × 10–16	158
359	H2O + O2(a 1Δ) → O2 + H2O	4.8 × 10–24	151
360	H2O + O2(b 1Σ) → O2 + H2O	3.9 × 10–18e125/Tg	151
361	HO2 + O → OH + O2	2.7 × 10–17e224/Tg	88 and 155
362	HO2 + O(1D) → OH + O2	5.2 × 10–16	As rxn 364
363	HO2 + O(1S) → OH + O2	5.2 × 10–16	As rxn 364
364	H2O2 + O(1D) → H2O + O2	5.2 × 10–16	159
365	H2O2 + O(1S) → H2O + O2	5.2 × 10–16	As rxn 364
366	O + O(1D) → 2O	8.0 × 10–18	160
367	O + O(1S) → 2O	3.33 × 10–17e–300/Tg	125 and 161 d
368	O + O(1S) → O(1D) + O	1.67 × 10–17e–300/Tg	125 and 161 d
369	O(1D) + O2 → O + O2	6.4 × 10–18	88
370	O(1D) + O2 → O + O2(b 1Σ)	2.56 × 10–17	88
371	O(1D) + O3 → 2O2	1.2 × 10–16	88
372	O(1D) + O3 → O2 + 2O	1.2 × 10–16	88
373	O(1S) + O3 → 2O2	1.2 × 10–16	As rxn 371
374	O(1S) + O3 → O2 + 2O	1.2 × 10–16	As rxn 372
375	O2 + O2(a 1Δ) → 2O2	3.0 × 10–24e–200/Tg	88
376	O2 + O2(b 1Σ) → O2 + O2(a 1Δ)	3.6 × 10–23T00.5	125
377	2O2(a 1Δ) → O2(b 1Σ) + O2	1.8 × 10–24T03.8e700/Tg	162 and 163
378	O2(a 1Δ) + O3 → O + 2O2	5.2 × 10–17e–2840/Tg	151
379	O2(b 1Σ) + O3 → O + 2O2	3.5 × 10–17e–135/Tg	151
Three-body collisions
380	2He + He* → He + He2*	2.0 × 10–46	164
381	He + He* + H2O → H2O+ + 2He + e	1.48 × 10–41	147 e
382	He + He* + O → O+ + 2He + e	8.2 × 10–42	As rxn 385
383	He + He* + O2 → O2+ + 2He + e	8.2 × 10–42	165
384	He + H + H → H2 + He	6.04 × 10–45T0–1.0	150 and 152 f
385	He + H + OH → H2O + He	9.23 × 10–44T0–1.527e–185/Tg	166 g
386	He + H + O → OH + He	4.36 × 10–44T0–1.0	167 c
387	(He+) H + O2 → HO2 (+He)	Effective	88 h , i
388	(He+) 2OH → H2O2 (+He)	Effective	88 h , j
389	He + 2O → O2 + He	3.99 × 10–47e900/Tg	167 k
390	He + O + O2 → O3 + He	3.66 × 10–46T0–2.6	88 l

^aIn m³ s^–1 and m⁶ s^–1 for two- and three-body collisions, respectively.

^bValue in an upper limit in reference.

^cEstimated value in reference.

^dEstimated branching ratio.

^eBranching ratios taken from Sanders.168

^fThird body is Ar instead of He in reference. The gas efficiency factor is assumed to be 1.

^gThird body is Ar instead of He in reference. The gas efficiency factor is assumed to be 0.65. This factor is calculated by dividing reaction rate coefficients for He and Ar as background gases for the same reaction measured by Zellner et al.169

^hEffective rate coefficients calculated from pressure dependent rates for 1 atm and fitted by an Arrhenius expression in the temperature range 280–350 K.

ⁱThird body is N₂ instead of He in reference. The gas efficiency factor is assumed to be 0.43. This factor is calculated by dividing reaction rate coefficients for He and N₂ as background gases for the same reaction measured by Hsu et al.170

^jRecommended rate coefficient in reference is for N₂ background gas instead of He. We apply a gas efficiency factor of 0.41 to the low-pressure limit reaction rate coefficient to account for this. This factor is calculated by dividing the room temperature rate coefficient from the given reference for He background gas (measured by Forster et al.171) by the recommended value (measured by Fulle et al.172).

^kThird body is Ar instead of He in reference. The gas efficiency factor is assumed to be 0.77. This factor is calculated by dividing reaction rate coefficients for He and Ar as background gases for the same reaction measured by Campbell and Thrush.169

^lThird body is N₂ instead of He in reference. The gas efficiency factor is assumed to be 0.61. This factor is calculated by dividing reaction rate coefficients for He and N₂ as background gases for the same reaction measured by Lin and Leu.173