A derivation of nano-diamond optical constants

% context {Nano-diamonds are an enticing and enigmatic dust component yet their origin is still unclear. They have been unequivocally detected in only a few astronomical objects, they the most abundant of pre-solar grains, both terms mass number.} %aims {Our goal to derive viable set nano-diamond optical constants properties enable modelling any type astrophysical object where, primarily, local (inter)stellar radiation field well-determined.} methods {The complex indices refraction, $m(n,k)$, nano-diamonds, constrained by available laboratory measurements, were calculated as function size, surface hydrogenation, internal (dis)order, using THEMIS a-C(:H) methodology optEC$_{\rm (s)}$(a).} results {To demonstrate utility (the efficiency factors $Q_{\rm ext}$, sca}$, abs}$), derived $m(n,k)$ data, we show that nano-diamonds could be interstellar medium (ISM) remain undetectable there.} conclusions provide means explore existence viability wide range sources. Here up percent carbon budget hidden form diffuse ISM, abundances comparable primitive meteorites.}