The high-resolution FTIR spectrum of the ν4 + ν8 band of trans-d2-ethylene (trans-C2H2D2)

► Analyzed the b-type feature of trans-C2H2D2ν4 + ν8 band for the first time. ► Derived accurate set of upper state rovibrational constants up to sextic terms. ► Derived ground state constants from 3340 GSCD.