Accurate ab initio Predictions of Ionization Energies and Heats of Formation for Cyclopropenylidene, Propargylene and Propadienylidene

The ionization energies （IEs） of cyclopropenylidene （c-C3H2）, propargylene （HCCCH） and propadienylidene （H2CCC） have been computed using the CCSD（T）/CBS method, which involves the approxixnation to the complete basis set （CBS） limit at the coupled cluster level with single and double excitations plus quasi-perturbative triple excitation effect （CCSD（T））. The zero-point vibrational energy correction, the core-valence electronic correction, the scalar relativistic effect and the high level correction beyond the CCSD（T） excitations have also been made in these calculations. The CCSD（T）/CBS values for the IN（c-C3H2） and IE（HCCCH） of 9.164, 8.987 eV are in good agreement with the experimental values of （9.15±0.03） and （8.96±0.04） eV. The CCSD（T）/CBS calculations yield the IE values of 10.477 and 10.388 eV for the ionization transitions H2CCC→H2CCC^＋ （^2A1, C2v） and H2CCC→H2CCC＋ （^2A＇, Cs）, respectively. On the basis of the Franek-Condon factor consideration, the IE of （10.43±0.02） eV determined in the previous single-photon ionization experiment most likely corresponds to the ionization threshold for the H2CCC→H2CCC^＋（^2A1, C2v） transition. Although the precision of the experimental IN measurements fpr c-C3H2, HCCCH, and H2CCC is insufficient to pin down the accuracy of the theoretical calculations to better than ±30 meV, the excellent agreement between the experimental and theoretical IE values observed in the present study indicates that the CCSD（T）/CBS calculations together with high-order correlation corrections are capable of yielding reliable IE predictions for simple hydrocarbon carbenes and bi-radicals. We have also reported the heats of formation at 0 K （△H^of0） and 298 K （△H^of298）for c-C3H2/c-C3H2^＋, HCCCH/HCCCH^＋, and H2CCC/H2CCC^＋, The available experimental △H^of0 and △H^of298 values for c-C3H2/c C3H2^＋, HCCCH/HCCCH^＋ are found to be in good accord with the CCSD（T）/CBS predictions after taking into account the experimental uncertainties.

State-to-state Photoionization Dynamics of Vanadium Nitride by Two-color Laser Photoionization and Photoelectron Methods

We have conducted a two-color visible-ultraviolet （VIS-UV） resonance-enhanced laser pho- toionization and pulsed field ionization-photoelectron （PFI-PE） study of gaseous vana- dium mononitride （VN） in the total energy range of 56900-59020 cm-1. The VN molecules were selectively excited to single rotational levels of the intermediate VN（D3H0, v＇=0） state by using a VIS dye laser prior to photoionization by employing a UV laser. This two-color scheme allows the measurements of rovibronically selected and re- solved PFI-PE spectra for the VN＋（X2A; v＋=0, 1, and 2） ion vibrational bands. By simulating the rotationally resolved PFI-PE spectra, J＋=3/2 is determined to be the lowest rotational level of the ground electronic state, indicating that the symmetry of the ground VN＋ electronic state is 2A3/2. The analysis of the PFI-PE spectra for VN＋ also yields accurate values for the adiabatic ionization energy for the formation of VN＋（X2A3/2）, IE（VN）=56909.5＋0.8 cm-1 （7.05588±0.00010 eV）, the vibrational fre- quency wc＋=1068.0±0.8 cm-1, the anharmonicity constant wc＋Xe＋=5.8±0.8 cm-1, the rotational constants Be＋=0.6563±0.0005 cm-1 and ae＋=0.0069±0.0004 cm-1, and the equi-librium bond length, re＋=1.529A, for VN＋（X2A3/2）; along with the rotational constants Bc＋=0.6578i0.0028 cm-1 and a＋=0.0085±0.0028 cm-1, and the equilibrium bond length re＋=1.527A for VN＋（X2As/2）, and the spin-orbit coupling constant A=153.3±0.8 cm-1 for VN＋（X2/k5/2,3/2）. The highly precise energetic and spectroscopic data obtained in the present study are valuable for benchmarking the predictions based on state-of-the-art ab initio quantum calculations.