Spectra of the D2O dimer in the O–D fundamental stretch region: The acceptor symmetric stretch fundamental and new combination bands

The O–D stretch fundamental region of the deuterated water dimer, (D2O)2, is further studied using a pulsed supersonic slit jet and a tunable optical parametric oscillator infrared source. The previously unobserved acceptor symmetric O–D stretch fundamental vibration is detected, with Ka = 0 ← 0 and 1 ← 0 sub-bands at about 2669 and 2674 cm−1, respectively. The analysis indicates that the various water dimer tunneling splittings generally decrease in the excited vibrational state, similar to the three other previously observed O–D stretch fundamentals. Two new (D2O)2 combination bands are observed, giving information on intermolecular vibrations in the excited O–D stretch states. The likely vibrational assignments for these and a previously observed combination band are discussed.