Table 5.

Summary of threshold energies for hydrogen chloride and methyl halides

Molecule	Ion	Threshold (eV)	Process	$\Delta H{f}_0^{°}$ (ion) (kcal mol−1)
HCI	HCI+	12.70	HCI + hv → HCI+ + e	270.9
	Cl+	17.34	→ Cl+ + H+e	326.2
CH3F	CH3F+	12.50	CH3F + hv → CH3F+ + e	a233.
	CH2F+	13.37	→ CH2F+ + H + e
	${\text{CH}}_3^{+}$	12.56	→${\text{CH}}_3^{+}+\text{F}$
		16.25	→${\text{CH}}_3^{+}+\text{F}+e$
	F−	12.59	→${\text{F}}^{-}+{\text{CH}}_3^{+}$
CH3Cl	CH3Cl+	11.28	CH3Cl + hv → CH3CI+ + e	242.7
	${\text{CH}}_3^{+}$	10.07	→${\text{CH}}_3^{+}+{\text{Cl}}^{-}$
		13.87	→${\text{CH}}_3^{+}+{\text{Cl}}^{-}+e$
	Cl−	10.07	→${\text{Cl}}^{-}+{\text{CH}}_3^{+}$
CH2DCl	CH2DCl+	11.29	CH2DCl + hv → CH2DCl+ + e	242.9
	CH2D+	10.10	→ CH2DCl+ + e
	Cl−
CHD2CI	CHD2CI+	11.30	CHD2CI + hv → CHD2CI+ + e	243.1
	${\text{CHD}}_2^{+}$	10.09	→${\text{CHD}}_2^{+}+{\text{Cl}}^{-}$
CD3Cl	CD3Cl+	11.30	CHD2CI + hv → CHD2CI+ + e	243.1
	${\text{CD}}_3^{+}$	13.8	→${\text{CD}}_3^{+}+{\text{Cl}}^{-}+e$
CH3Br	CH3Br+	10.53	CH3Br + hv → CH3Br+ + e	238.1
		(10.81)
	${\text{CH}}_3^{+}$	12.77	→${\text{CH}}_3^{+}+\text{Br}+e$	261.6

^aAssuming ΔHf(CH₃F) = −55 kcal mol⁻¹ from ref. 27.