Global Potential Energy Surface for HO2+ Using the CHIPR Method

Accurate diabatization based on combined-hyperbolic-inverse-power-representation: 1,2 2A' states of BeH2

A diabatic potential energy matrix (DPEM) for the two lowest states of BeH2+ has been constructed using the combined-hyperbolic-inverse-power-representation (CHIPR) method. By imposing symmetry constraints on the coefficients of polynomials, the complete nuclear permutation inversion symmetry is correctly preserved in the CHIPR functional form. The symmetrized CHIPR functional form is then used in the diabatization by ansatz procedure. The ab initio energies are reproduced with satisfactory accuracy. In addition, the CHIPR-based DPEM also reproduces the local topology of a conical intersection. Future work will focus on a complete four-state diabatic representation with emphasis on the long-range interactions and spin-orbit couplings, which will enable accurate quantum scattering calculations for the Be+(2P) + H2 → BeH+(X1Σ+) + H(2S) reaction.

A global CHIPR potential energy surface of PH2(X2B1) via extrapolation to the complete basis set limit and the dynamics of P(2D) + H2(X1Σ+g) → PH(X3Σ−) + H(2S)

A global PEC of the ground state PH2 was constructed using the CHIPR method based on accurate MRCI(Q)/CBS(T, Q) energy points. The ICS and k(T) of P(2D) + H2(X1Σ+g) → PH(X3Σ−) + H(2S) were calculated based on the QCT method.

Threshold photoelectron spectroscopy of the HO2 radical

We report a synchrotron radiation vacuum ultraviolet photoionization study of the hydroperoxyl radical (HO₂), a key reaction intermediate in combustion and atmospheric chemistry as well as astrochemistry, using double imaging photoelectron photoion coincidence spectroscopy. The HO₂ radical is formed in a microwave discharge flow tube reactor through a set of reactions initiated by F atoms in a CH₄/O₂/He gas mixture. The high-resolution threshold photoelectron spectrum of HO₂ in the 11 eV-12 eV energy range is acquired without interferences from other species and assigned with the aid of theoretically calculated adiabatic ionization energies (AIEs) and Franck-Condon factors. The three vibrational modes of the radical cation HO₂ ⁺, the H-O stretch, the H-O-O bend, and the O-O stretch, have been identified, and their individual frequencies are measured. In addition, the AIEs of the X³A″ ground state and the a¹A' first excited electronic state of HO₂ ⁺ are experimentally determined at 11.359 ± 0.003 eV and 11.639 ± 0.005 eV, respectively, in agreement with high-level theoretically computed results. Furthermore, the former AIE value provides validation of thermochemical networks used to extract the enthalpy of formation of the HO₂ radical.

Accurate Potential Energy Surface for Quartet State HN2 and Interplay of N(4S) + NH(X̃3Σ-) versus H + N2(A3Σu+) Reactions

A global potential energy surface for the lowest quartet state of HN₂ is reported for the first time from accurate multireference ab initio calculations extrapolated to the complete basis set limit using the double many-body expansion method. All its stationary points are characterized, with the lowest quartet of HN₂ predicted to have a bent global minimum 36 kcal mol^-1 below the N(⁴S) + NH(X̃³Σ^-) asymptote, from which it is barrierlessly achievable. The entire set of calculated ab initio points has been fitted for energies up to 1000 kcal mol^-1 above the global minimum with an RMSD of 0.89 kcal mol^-1, a gap comprising all identified stationary points. Special care is taken in modeling the involved long-range forces and cusps caused by crossing seams. The novel PES prompts for the calculation of rate constants for several unexplored reactions that are relevant for combustion, plasma, and atmospheric chemistry.