The weakly-bound CO2-acetylene complex: Fundamental and torsional combination band in the CO2ν3 region

► We studied spectra of CO2-C2H2 in the region of CO2ν3 fundamental. ► A b-type band with a vibrational shift of −0.5 cm−1 was assigned to the fundamental. ► A weaker band was identified as the torsional combination band by its c-type structure. ► The resulting torsional frequency is 44.385(10) cm−1.