Bethlem, H. L., Berden, G., Crompvoets, F. M. H., Jongma, R. T., van Roij, A. J. A., & Meijer, G. (2000). Electrostatic trapping of ammonia molecules. Nature, 406, 491-494. https://doi.org/10.1038/35020030 (Original work published 2000)