Table 2: Sources for double-ionisation cross sections, either from theoretical estimates or from laboratory measurements.
Ionisation Photoionisation

${\rm N_2} \rightarrow {\rm N_2}^{++} + 2 {\rm e}^-$ Simon et al. (2005) theoretical estimates

This work, based on Samson (1990)

${\rm O} \rightarrow {\rm O}^{++} + 2 {\rm e}^-$ Fennelly & Torr (1992)

Angel & Samson (1988)

${\rm CO_2} \rightarrow {\rm CO_2}^{++} + 2 {\rm e}^-$ Masuoka (1994)

Baluja & Zeippen (1988)

${\rm O}^+ \rightarrow {\rm O}^{++} + {\rm e}^-$ Kjeldsen et al. (2002)

Aguilar et al. (2003)

Ionisation Electron impact

Krishnakumar & Srivastava (1990)

Märk (1975)

${\rm N_2} \rightarrow {\rm N_2}^{++} + 2 {\rm e}^-$ Halas & Adamczyk (1972)

Straub et al. (1996)

Itikawa & Ichimura (1990)

${\rm O} \rightarrow {\rm O}^{++} + 2 {\rm e}^-$ Zipf (1985)

Ziegler et al. (1982)

${\rm CO_2} \rightarrow {\rm CO_2}^{++} + 2 {\rm e}^-$ Tian & Vidal (1998)

${\rm O}^+ \rightarrow {\rm O}^{++} + {\rm e}^-$ Aitken & Harrison (1971)

Yamada et al. (1988)

**Table 2:** Sources for double-ionisation cross sections, either from theoretical estimates or from laboratory measurements.
Ionisation	Photoionisation
${\rm N_2} \rightarrow {\rm N_2}^{++} + 2 {\rm e}^-$	Simon et al. (2005) theoretical estimates
	This work, based on Samson (1990)
${\rm O} \rightarrow {\rm O}^{++} + 2 {\rm e}^-$	Fennelly & Torr (1992)
	Angel & Samson (1988)
${\rm CO_2} \rightarrow {\rm CO_2}^{++} + 2 {\rm e}^-$	Masuoka (1994)
	Baluja & Zeippen (1988)
${\rm O}^+ \rightarrow {\rm O}^{++} + {\rm e}^-$	Kjeldsen et al. (2002)
	Aguilar et al. (2003)
Ionisation	Electron impact
	Krishnakumar & Srivastava (1990)
	Märk (1975)
${\rm N_2} \rightarrow {\rm N_2}^{++} + 2 {\rm e}^-$	Halas & Adamczyk (1972)
	Straub et al. (1996)
	Itikawa & Ichimura (1990)
${\rm O} \rightarrow {\rm O}^{++} + 2 {\rm e}^-$	Zipf (1985)
	Ziegler et al. (1982)
${\rm CO_2} \rightarrow {\rm CO_2}^{++} + 2 {\rm e}^-$	Tian & Vidal (1998)
${\rm O}^+ \rightarrow {\rm O}^{++} + {\rm e}^-$	Aitken & Harrison (1971)
	Yamada et al. (1988)