I have a paper due about the isomers of nitrous acid, using various calculations methods to find molecular properties like their dipole moment. I've found the dipole moment of trans isomer to be 1.987 and the dipole moment of cis to be 1.458. I've also found that ALL bond angles are bigger for cis, and most bond lengths are longer for cis, other than N-O (single bond) which is longer for trans. Also if that helps, the HOMO and LUMO orbitals of trans have a bigger overlap in the N-O bond.
I know that the longer the bond, the bigger the charge separation, thus a bigger dipole moment, which doesn't seem to match my data and the literature, as the bonds are longer in cis (also checked the distance between the oxygens in both isomers). Does it have anything to do with the N-O bond being longer for trans, as the dipole moment for trans is bigger?
I'm matching my data to "Microwave Spectrum, Structure, Dipole Moment and Quadrupole Coupling Constants of cis and trans Nitrous Acids" by A. Peter Cox, Alan H. Brittain and David J. Finnigan from 1970 (The article is quite old but it's the first one I had found, and it is very similar to more recent ones).