Sympathetic cooling of molecular ions with ultracold atoms

EPJ Techniques and Instrumentation

Table 2 Properties of potential ultracold atomic buffer gases

Atom	IP [eV]	λ [nm]	IP/(hc/ λ)	m [amu]
Hg	10.437504	254	2.14	201
Zn	9.3941990	214	1.62	65
Be	9.322699	235	1.77	9
Cd	8.993822	229	1.66	112
Mg	7.646235	285	1.76	24
Cr	6.76651	425	2.32	52
Yb	6.254159	399	2.01	173
Tm	6.18431	410	2.04	169
Ca	6.11315520	423	2.09	40
Er	6.1077	583	2.87	167
Ho	6.0215	410	1.99	165
Dy	5.93905	421	2.02	162
Sr	5.69486720	461	2.12	88
Li	5.391714761	671	2.92	7
Ba	5.211664	554	2.33	137
Na	5.1390767	589	2.44	23
K	4.34066354	767	2.69	39
Rb	4.177128	780	2.63	85

The second column shows the energy required to ionize the atom, which is a indicative of its reactivity with candidate ions. The third column shows the lowest wavelength required for laser cooling of the atom. The shorter the wavelength the more potential there is for problem such as unwanted ionization, dissociation, or production of photoelectrons. The fourth column is the approximate number of laser cooling photons required to reach the ionization energy of the atom. The fifth column shows the mass of the atom for reference. Roughly speaking, efficient cooling is only possible for ions with a mass roughly two to three times this mass