There are 3 references in total for K.

1. Allard, N. F., Spiegelman, F., Leininger, T. Molliere, P., "New study of the line profiles of sodium perturbed by H2", Astronomy and Astrophysics 628, A120 (2019).
2. Allard, N. F. and Spiegelman, F. and Kielkopf, J. F, "K-H2 line shapes for the spectra of cool brown dwarfs", A&A 589, A21 (2016). [link to article]
3. Scherf, W., Khait, O., J\"ager, H. and Windholz, L., "Re-measurement of the transition frequencies, fine structure splitting and isotope shift of the resonance lines of lithium, sodium and potassium", Zeitschrift fur Physik D 36, 31-33 (1996).[scherf:1996]

The ExoMol bibliometrician is Olga Yurchenko