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  1. The kinetic energy dependent reactions of Re + with SO 2 were studied with guided ion beam tandem mass spectrometry. ReO + , ReO 2 + , and OReS + species were observed as products, all in endothermic reactions. Modeling of the kinetic energy dependent cross sections yields 0 K bond dissociation energies (BDEs, in eV) of 4.78 ± 0.06 (Re + –O), 5.75 ± 0.02 (Re + –O 2 ), and 4.35 ± 0.14 (Re + –SO). The latter two values can be combined with other information to derive the additional values 6.05 ± 0.05 (ORe + –O) and 4.89 ± 0.19 (ORe + –S). BDEs of ReO + and ReO 2 + agree with literature values whereas the values for OReS + are the first measurements. The former result is obtained even though formation of ground state ReO + is spin-forbidden. Quantum mechanical calculations at the B3LYP level of theory with a def2-TZVPPD basis set yield results that agree reasonably well with experimental values. Additional calculations at the BP86 and CCSD(T) levels of theory using def2-QZVPPD and aug-cc-pVxZ (x = T, Q, and 5) basis sets were performed to compare thermochemistry with experiment to determine that ReO 2more »+ rather than the isobaric ReS + is formed. Product ground states are 3 Δ 3 (ReO + ), 3 B 1 (OReO + ), 5 Π −1 (ReS + ), and 3 A′′(OReS + ) after including empirical spin–orbit corrections, which means that formation of ground state products is spin-forbidden for all three product channels. The potential energy surfaces for the ReSO 2 + system were also explored at the B3LYP/def2-TZVPPD level and exhibited no barriers in excess of the endothermicities for all products. BDEs for rhenium oxide and sulfide diatomics and triatomics are compared and discussed. The present result for formation of ReO + is compared to that for formation of ReO + in the reactions of Re + + O 2 and CO, where the former system exhibited interesting dual cross section features. Results are consistent with the hypothesis that the distinction of in-plane and out-of-plane C S symmetry in the triatomic systems might be the explanation for the two endothermic features observed in the Re + + O 2 reaction.« less
  2. Complexes of 18-crown-6 ether (18C6) with four protonated amino acids (AAs) are examined using infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light generated by the infrared free electron laser at the Centre Laser Infrarouge d’Orsay (CLIO). The AAs examined in this work include glycine (Gly) and the three basic AAs: histidine (His), lysine (Lys), and arginine (Arg). To identify the (AA)H + (18C6) conformations present in the experimental studies, the measured IRMPD spectra are compared to spectra calculated at the B3LYP/6-311+G(d,p) level of theory. Relative energies of various conformers and isomers are provided by single point energy calculations carried out at the B3LYP, B3P86, M06, and MP2(full) levels using the 6-311+G(2p,2d) basis set. The comparisons between the IRMPD and theoretical IR spectra indicate that 18C6 binds to Gly and His via the protonated backbone amino group, whereas protonated Lys prefers binding via the protonated side-chain amino group. Results for Arg are less definitive with strong evidence for binding to the protonated guanidino side chain (the calculated ground conformer at most levels of theory), but contributions from backbone binding to a zwitterionic structure are likely.