Dynamics of Electronically Excited Metal Atoms (Zn and Cd) in Rare Gas Matrices: Simulation of Multiple-band Emission Using Molecular Dynamics with Quantum Transitions

A Molecular Dynamics with Quantum Transitions approach is employed to simulate the spectroscopic characteristics of the 1P1↔1S0 transitions of atomic zinc and cadmium in order to gain insight into the excited state behavior of these atoms isolated in the solid rare gases neon, argon and krypton. The absorption and emission spectra are simulated. Non-radiative processes play a fundamental role in the transfer of population among the three electronic states initially accessed in absorption. It has been possible to identify three distinct relaxation pathways. Two of these are related to the dynamical modes described in previous works [McCaffrey and Kerins, J. Chem. Phys.106, 7885 (1997); Kerins and McCaffrey, J. Chem. Phys.109, 3131 (1998)] in which the system evolves to form a square planar configuration around the metal atom. The third distinct pathway involves motion on a hexagonal close packed plane. The temperature dependences of complex formation were also determined for the three relaxation pathways.

Strong ortho/para effects in the vibrational spectrum of Cl-(H2)

The predissociation spectrum of the Cl-35(H₂) complex is measured between 450 and 800 cm^-1 in a multipole radiofrequency ion trap at different temperatures using the FELIX infrared free electron laser. Above a certain temperature, the removal of the Cl^-(p-H₂) para nuclear spin isomer by ligand exchange to the Cl^-(o-H₂) ortho isomer is suppressed effectively, thereby making it possible to detect the spectrum of this more weakly bound complex. At trap temperatures of 30.5 and 41.5 K, we detect two vibrational bands of Cl^-(p-H₂) at 510(1) and 606(1) cm^-1. Using accurate quantum calculations, these bands are assigned to transitions to the inter-monomer vibrational modes (v₁,v₂ ^l₂ ) = (0, 2⁰) and (1, 2⁰), respectively.

Correction: Quantum tunneling dynamical behaviour on weakly bound complexes: the case of a CO2-N2 dimer

Correction for 'Quantum tunneling dynamical behaviour on weakly bound complexes: the case of a CO2-N2 dimer' by Miguel Lara-Moreno et al., Phys. Chem. Chem. Phys., 2019, 21, 3550-3557, DOI: 10.1039/c8cp04465a.

Predissociation spectra of the 35Cl-(H2) complex and its isotopologue 35Cl-(D2)

The predissociation spectra of the 35Cl-(H2) and 35Cl-(D2) complexes are determined within an accurate quantum approach and compared to those recently measured in an ionic trap at 8 K and 22 K. The calculations are performed using an existing three-dimensional potential energy surface. A variational approach is used for the accurate quantum calculations of the rovibrational bound states. Several methods are compared for the search and the characterization of the resonant states. A good agreement between the calculated and measured spectra is obtained, despite a slight shift to the red of the calculated spectra. The comparison shows that only the ortho or para contribution is observed in the measured 35Cl-(H2) or 35Cl-(D2) spectrum, respectively. Quantum numbers are assigned to the rovibrational resonant states. It demonstrates that the main features observed in the measured predissociation spectra correspond to a progression in the intermonomer vibrational stretching mode.

Potential energy surface and rovibrational bound states of the H2-C3N- van der Waals complex

Since their recent detection in the interstellar medium, anions have raised the question of their possible mechanisms of formation, destruction and excitation. This requires knowledge of their interaction with the most abundant interstellar species. In the present work, a four dimensional rigid rotor model of the potential energy surface is developed for the collision of C3N- with H2. Ab initio calculations are performed with explicitly-correlated coupled-cluster theory via CCSD(T)-F12/aug-cc-pVTZ. Two linear equilibrium structures are found, different in the orientation of C3N-. Two more equilibrium structures, symmetrically equivalent, are obtained by the permutation of H atoms. The vibrational dynamics is mainly controlled by the considerable difference between the two bending frequencies that correspond to the hindered rotations of C3N- and H2. This arises from the potential energy surface which is soft for rotation of C3N- and stiff for rotation of H2, and also from the large difference in mass between both monomers. Although a high potential barrier prevents the rotation of H2, a significant tunneling effect is observed which causes a splitting in the degenerate energy levels. On the contrary, the rotation of C3N- is allowed since the energy of the saddle points is lower than the energy of the bound states, but the wavefunctions remain localized around each linear structure unless a large excitation energy is available.

Quantum tunneling dynamical behaviour on weakly bound complexes: the case of a CO2–N2 dimer

The dynamics induced by quantum tunneling is found to be closely connected to the shape of the potentials for weakly bound complexes.

On the gas-phase formation of the HCO- anion: accurate quantum study of the H- + CO radiative association and HCO radiative electron attachment

The hydrogen anion has never been observed in the interstellar medium, but it is most likely present in some interstellar regions. Since direct detection appears especially difficult, improving the knowledge of the astrochemical processes involving this anion should be valuable in defining a way of indirect detection. We present the first study of the radiative association of H- and CO to form the HCO- anion within a quantum time-independent approach. We use a state-of-the-art potential energy surface which has been calculated for the present study. The calculated radiative association rate coefficient is monotonically decreasing from 6 × 10-16 to 5 × 10-19 cm3 per molecule per s across the 0.01-1000 K temperature range. At the typical temperature of the cold interstellar medium, ∼10 K, the radiative association rate is ∼2 × 10-17 cm3 per molecule per s. On the other hand, the plane wave approximation is used to calculate the HCO radiative electron attachment rate coefficient. It is found to be almost constant and also equal to 2 × 10-17 cm3 per molecule per s. Setting aside the question of the abundances of the reactants of both processes, these results demonstrate that among the two gas-phase modes of production of the HCO- anion in cold interstellar medium considered in this study, the H- + CO radiative association is dominating below 10 K while the radiative electron attachment rate is larger above 10 K.