Deuterated ions are abundant in cold (T=10 K), dense (n=10^5 cm^-3) regions, in which CO is frozen out onto dust grains. In such environments, the deuterium fractionation of such ions can exceed the elemental abundance ratio of D/H by a factor of 10^4. In this paper we use the deuterium fractionation to investigate the evolutionary state of Class 0 protostars. In a sample of 20 protostellar objects, we found a clear correlation between the N2D+/N2H+ ratio and evolutionary tracers. As expected, the coolest, i.e. the youngest, objects show the largest deuterium fractionation. Furthermore, we find that sources with a high N2D+/N2H+ ratio show clear indication for infall.
@article{arxiv.0809.3759,
title = {The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars},
author = {M. Emprechtinger and P. Caselli and N. H. Volgenau and J. Stutzki and M. C. Wiedner},
journal= {arXiv preprint arXiv:0809.3759},
year = {2009}
}