Search for exchange-antisymmetric states for spin-0 particles at the 10(-11) level

We set a new upper limit of 1.7 x 10(-11) to the probability that two spin- 0 O-16 nuclei are in forbidden exchange-antisymmetric states. testing the v alidity of fundamental principles of quantum mechanics. A newly designed di fference-frequency spectrometer is used to look for the existence of these states. The experimental test was performed by tuning the spectrometer acro ss a molecular transition of (CO2)-C-12-O-16 belonging to the rovibrational band at 4.25 mum, connecting the forbidden states (00(0)0, J = 25) and (00 (0)1, J = 26).