3. Characteristic Temperature T _VLT for Transition to the Classical Langevin Capture Rate in Collisions of Diatomic Hydrogen Isotopologues with Selected Diatomic and Polyatomic Isotopologues .

Molecular Ion	Neutral Molecule	TVLT [mK]
H2	H2	17.2
	HD	12.0
	D2	9.70
HD+	H2	12.0
	HD	7.65
	D2	5.86
D2	H2	9.70
	HD	5.86
	D2	4.30
H3	H2	12.0
	HD	7.65
	D2	5.86
H2D+	H2	9.70
	HD	5.86
	D2	4.30
HD2	H2	8.43
	HD	4.90
	D2	3.48
D3	H2	7.65
	HD	4.30
	D2	3.00
CH3	H2	5.53
	HD	2.75
	D2	1.73
C2H2	H2	5.00
	HD	2.38
	D2	1.43

^aNote all temperatures considered occur in the cold regime well below 1 K. Adapted from E. I. Dashevskaya and I. Litvin, Rates of complex formation in collisions of rotationally excited homonuclear diatoms with ions at very low temperatures: Application to hydrogen isotopes and hydrogen-containing ions, Journal of Chemical Physics, 122 (2005) 184311, with the permission of AIP Publishing.