The microwave and infrared spectra of CO–(pH2)2, CO–(oD2)2, and CO–pH2–He trimers are predicted by performing exact bound state calculations on the global potential energy surfaces defined as the sum of accurately known two-body pH2–CO or oD2–CO (in Li et al. J Chem Phys 139:164315, 2013), pH2–pH2 or oD2–oD2 (in Patkowski et al. J Chem Phys 129:094304, 2008), and pH2–He pair potentials. A total of four transitions have been reported to date, three in the infrared region, and one in the microwave region, which are in good agreement with our theoretical predictions. Based on selection rules, new transitions for J ≤ 3 have been predicted, and the corresponding transition intensities at different temperatures are also calculated. These predictions will serve as a guide for new experiments. The weak and tentatively assigned transitions are verified by our calculations. Three-body effects and the quality of the potential are discussed. A reduced-dimension treatment of the pH2 or oD2 rotation has been employed by applying the hindered-rotor averaging technique of Li et al. (J Chem Phys 133:104305, 2010). A technique for displaying the three-dimensional pH2 or oD2 density in the body-fixed frame is used and shows that in the ground state, the two pH2 or two oD2 molecules are localized, while the He’s are delocalized.
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The authors thank Professor Piotr Jankowski (Nicolaus Copernicus University) for providing us with his V12 potential for the H2–CO complex. This research has been supported by the National Natural Science Foundation of China (Grant Nos. 21003058 and 21273094), the Program for New Century Excellent Talents in University, and the Natural Sciences and Engineering Research Council of Canada (NSERC). We acknowledge the High Performance Computing Center (HPCC) of Jilin University for supercomputer time.