On azimuthal angle difference between two jets

I want to compute the distribution of azimuthal angle difference \Delta \phi (j_1, j_2) between the leading and subleading jets. However, none of PHI( j[1] j[2] ) , dsPHI( j[1] j[2] ) , dvPHI( j[1] j[2] ) , sPHI( j[1] j[2] ) commands gives the correct distribution. What commands should I use for this purpose? Thank you very much!