Thermochemical properties of small rhenium molecules: ReC, ReN, ReO, ReS, and ReC2

The rhenium-containing molecules ReC, ReN, ReO, ReS, and ReC2 have been investigated using a pulsed laser ablation supersonic beam molecular source in resonant two-photon ionization experiments with time-of-flight mass spectrometric detection. Sharp predissociation thresholds have been observed, allowing precise bond dissociation energies (BDEs) to be measured as D0(ReC) = 5.731(3) eV, D0(ReN) = 5.635(3) eV, D0(ReO) = 5.510(3) eV, D0(ReS) = 3.947(3) eV, and D0(Re-C2) = 5.359(3) eV. The threshold for two-photon ionization was also measured for ReC, ReN, and ReO, providing ionization energies (IEs) of IE(ReC) = 8.425(12) eV, IE(ReN) = 8.193(20) eV, and IE(ReO) = 8.561(11) eV. These are the first measurements of these thermochemical quantities to be reported in the literature. The combination of BDEs and IEs allowed the BDEs of the cations ReC+, ReN+, and ReO+ to be determined via a thermochemical cycle as D0(Re+-C) = 5.140(12) eV, D0(Re+-N) = 5.275(20) eV, and D0(Re+-O) = 4.783(11) eV. In addition, computations of these thermochemical values were performed using density functional theory [B3LYP/aug-cc-pVQZ(-PP)] to determine the ground states and their geometric parameters. These were further studied at the CCSD(T) level with extrapolation to the complete basis set limit using aug-cc-pVXZ(-PP) basis sets (X = 3, 4, 5) to obtain computational values of the BDEs and IEs as well. The high-level super correlation consistent composite approach (s-ccCA) was also utilized, providing an additional approach for the prediction of thermochemical values. The electronic structure of the molecules is discussed, along with the periodic trends as the ligand is varied.