Structural and spectroscopic properties of the diazocarbene radical (CNN) and its ions CNN+and CNN−: a high-level theoretical investigation

Hyperthermal Dynamics and Kinetics of the C(3P) + N2(X1Σg+) → CN(X2Σ+) + N(4S) Reaction

The hyperthermal dynamics and kinetics of the title reaction, which plays an important role in hypersonic chemistry for atmospheric entry vehicles, are investigated using quasi-classical trajectory methods on a recently developed ground electronic state potential energy surface. The dynamics calculations indicated that the reaction follows a complex-forming mechanism, despite its large endoergicity. The calculated differential cross section is forward-backward symmetric, consistent with a long-lived reaction intermediate supported by the NCN potential well. The lifetime of the reaction complex is sufficiently long that the vibrational distribution of the CN product can be predicted by the phase space theory. The calculated vibrational state specific and thermal rate coefficients follow the Arrhenius behavior, and the agreement with existing low-temperature experimental thermal rate coefficients is satisfactory. Extrapolations to high temperatures relevant to hypersonic conditions are provided.

Electronic Structure and Bonding of the Fastidious Species CN2 and CP2: A First-Principles Study

The transient molecular species CN₂ (CNN, NCN, c(yclic)-CN₂) and CP₂ (CPP, PCP, c(yclic)-CP₂), along with the isoelectronic to CNN and isovalent to CPP, CCO, have been studied theoretically through the ab initio methodologies multireference configuration interaction (MRCI) and RCCSD(T) coupled with augmented correlation-consistent quintuple and sextuple basis sets. For the CNN, NCN, and c-CN₂ molecules, the examined states are [X̃³Σ^-, ã¹Δ, b̃¹Σ⁺, óΠ, and c̃¹Π], X̃³Σ_g^-, and X̃¹A₁, respectively. The analogous phosphorous system CPP has been studied theoretically for the first time. Our results show that the symmetries ³Σ^-, ¹Δ, and ¹Σ⁺ are not stationary states; thence, the ground state of CPP is of ³Π symmetry and of similar electronic structure to that of the Ã³Π state of CNN. For most of the symmetries studied, we have constructed fully optimized potential energy profiles or "cuts" through the corresponding surfaces at the MRCI level of theory in an effort to follow the (valence) electronic distributions from the "selected" adiabatic species to equilibrium. Our numerical results are in excellent agreement with existing experimental data and previous, although limited, high-level ab initio calculations. Finally, it should be said that some of our findings like dissociation energies, permanent electric dipole moments, and bonding considerations are addressed for the first time.

First-principles dynamics of collisional intersystem crossing: resonance enhanced quenching of C(1D) by N2

Intersystem crossing is a common and important nonadiabatic process in molecular systems. Revealed with a first-principles investigation, the quenching of C(¹D) by N₂ is efficient due to multiple passages via long-lived collisional resonances, despite relatively small spin–orbit couplings.