Johnson Eric L, Davis Quincy C, Morse Michael D
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
J Chem Phys. 2016 Jun 21;144(23):234306. doi: 10.1063/1.4953782.
The abrupt onset of predissociation in the congested electronic spectra of jet-cooled VC, VN, and VS has been observed using resonant two-photon ionization spectroscopy. It is argued that because of the high density of electronic states in these molecules, the predissociation threshold occurs at the thermochemical threshold for the production of separated atoms in their ground electronic states. As a result, the measured threshold represents the bond dissociation energy. Using this method, bond dissociation energies of D0(V C) = 4.1086(25) eV, D0(V N) = 4.9968(20) eV, and D0(V S) = 4.5353(25) eV are obtained. From these values, enthalpies of formation are derived as Δf,0KH°(V C(g)) = 827.0 ± 8 kJ mol(-1), Δf,0KH°(V N(g)) = 500.9 ± 8 kJ mol(-1), and Δf,0KH°(V S(g)) = 349.3 ± 8 kJ mol(-1). Using a thermochemical cycle and the well-known ionization energies of V, VC, and VN, our results also provide D0(V(+)-C) = 3.7242(25) eV and D0(V(+)-N) = 4.6871(20) eV. These values are compared to previous measurements and to computational results. The precision of these bond dissociation energies makes them good candidates for testing computational chemistry methods, particularly those that employ density functional theory.
利用共振双光子电离光谱法，在喷射冷却的VC、VN和VS的密集电子光谱中观察到预解离的突然出现。有人认为，由于这些分子中电子态的高密度，预解离阈值出现在其基态电子态中产生分离原子的热化学阈值处。因此，测量到的阈值代表键解离能。使用这种方法，得到了D0(VC) = 4.1086(25) eV、D0(VN) = 4.9968(20) eV和D0(VS) = 4.5353(25) eV的键解离能。根据这些值，推导出形成焓为Δf,0KH°(VC(g)) = 827.0 ± 8 kJ mol(-1)、Δf,0KH°(VN(g)) = 500.9 ± 8 kJ mol(-1)和Δf,0KH°(VS(g)) = 349.3 ± 8 kJ mol(-1)。利用热化学循环以及V、VC和VN的已知电离能，我们的结果还给出了D0(V(+)-C) = 3.7242(25) eV和D0(V(+)-N) = 4.6871(20) eV。将这些值与先前的测量结果和计算结果进行了比较。这些键解离能的精度使其成为测试计算化学方法的良好候选对象，特别是那些采用密度泛函理论的方法。
