Table 1
Recommended charge-changing cross section polynomial fits for (He2+, He+, and He0) projectiles colliding with H2O vapor.
| Cross section | Degree | Coefficients | Validity range | Confidence | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| (m2) | n | p0 | p1 | p2 | p3 | p4 | p5 | vi (km s−1) | Ei (keV u−1) | |
| σ21 | 4 | − 129.6349 | 85.3069 | − 25.7100 | 3.50927 | − 0.18016 | – | 75–5350 | 0.03–150 | High |
| σ20 | 5 | 3327.3456 | − 3277.1313 | 1272.0445 | − 244.7593 | 23.35760 | − 0.88492 | 100–5350 | 0.05–150 | High |
| σ12 | 4 | − 314.9414 | 205.4565 | − 57.4465 | 7.3111 | − 0.34819 | – | 820–10 000 | 3.50–520 | High |
| σ10 | 5 | − 5450.8180 | 4667.4695 | − 1592.4968 | 269.5820 | − 22.63262 | 0.75346 | 120–5000 | 0.08–130 | High |
| σ02 | 2 | − 245.4003 | 66.2165 | − 4.8686 | – | – | – | 3800–9300 | 75.0–450 | Low |
| σ01 | 2 | − 98.7467 | 24.0604 | − 1.8252 | – | – | – | 310–10 000 | 0.50–520 | Low |
Notes. The polynomial, function of the speed of the impactor, is of the form
, where n is the degree of the fit, the speed vi is expressed in m s−1, and the cross section σ in m2. Ranges of validity for impact speeds and energies are given. Confidence levels on the fits are indicated: high (< 25%), medium (25– 75%), and low (> 75%).
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