Theoretical calculation about the valence and rydberg excited states of hydrogen cyanide

Abstract

The singlet and triplet excited states of hydrogen cyanide have been computed by using the complete active space self-consistent field and completed active space second order perturbation methods with the atomic natural orbital (ANO-L) basis set. Through calculations of vertical excitation energies, we have probed the transitions from ground state to valence excited states, and further extensions to the Rydberg states are achieved by adding 1s1p1d Rydberg orbitals into the ANO-L basis set. Four singlet and nine triplet excited states have been optimized. The computed adiabatic energies and the vertical transition energies agree well with the available experimental data and the inconsistencies with the available theoretical reports are discussed in detail.

The 1 3A′ HCN and 1 3A′ HCO+ Vibrational Frequencies and Spectroscopic Constants from Quartic Force Fields

“…The equilibrium geometries of 1 3 A′ HCN, given in Table , differ between our CCSD­(T)/aug-cc-pV5Z results modified to include core-correlation effects and the CASPT2/ANO-L geometry from Li and co-workers . Mainly, we are predicting a 0.011 Å shorter C–N bond and a 120.587° bond angle instead of 121.7°.…”

“…The excitation removes an electron from a π bonding orbital along the axis of the molecule and excites it into a π antibonding orbital giving a bent structure with a (core) 3a′ 2 4a′ 2 5a′ 2 1a″ 2 6a′ 1 7a′ 1 configuration. This has been known for HCN where adiabatic computations put the excitation energy at 4.44 eV (EOM-CCSD/aug-cc-pVTZ from ref ) and 4.69 eV (CASPT2/ANO-L from ref ). Our CCSD­(T)/aug-cc-pV5Z computations adiabatically predict the 1 3 A′ state of HCN to lie 4.84 eV above the X̃ 1 Σ + state, somewhat above the previous computations.…”

“…Data from theoretical computations − indicates that the first excited state for these systems are triplet (1 3 A′) states that lie more than 4 eV above the ground state. The photochemistry of regions in which these interstellar molecules are known to exist such as the Orion Molecular Cloud or the atmospheres of Jupiter or Titan , are chemically active enough ,, for the 1 3 A′ states of both HCN and HCO + to be observed rotationally or potentially even vibrationally.…”

State-to-state quantum dynamics of the N(4S) + CH(X 2Π) → CN(X 2Σ+,A2Π) + H(2S) reactions

“…22,[24][25][26] The geometries of the stationary points are similar with the results of Rayez et al, 22 while the relative energies are much lower than theirs. For the equilibrium geometry of the 1 3 A state, our prediction (2.081 bohr, 2.447 bohr, 121.5 • ) shows a better agreement with the CCSD(T)/augcc-pV5Z results (2.081 bohr, 2.433 bohr, 120.6 • ) from Fortenberry at al.…”

State‐to‐state reaction dynamics for the reactions of atom N with radicals

“…In addition, they calculated some parts of the conical intersection which are energetically lower that the ground state reactants, indicating that transitions between surfaces should play an important role in the N + CH reaction dynamics . In subsequent years, different theoretical methods have been used to study the characteristics of excited triplet states of HCN . Thürwächter and Halvick presented a procedure for computing a global ab initio quasi‐diabatic representation for the reaction N + CH → CN + H .…”