Collective mode frequency shifts in l-serine and a series of isotopologues in the terahertz regime

► l-Serine and l-serine isotopologues studied in the terahertz regime. ► Mass related frequency shifts observed at room and liquid nitrogen temperature. ► Atom crystal lattice dependence correlated to observed collective modes. ► Peaks 1 and 2 at RT exhibit have greater shifts with non-hydrogen bonding atoms. ► Peaks 1 and 3 at LN2 temperature follow RT trend while peak 2 has equal dependence.