Aristophanes Metropoulos

An accurate description of the ground and excited states of SiH

With the high accuracy afforded by the sextuple correlation consistent basis set of Dunning, we have calculated energy levels, dissociation energies, equilibrium distances, and other spectroscopic constants for eleven valence and four Rydberg states of the CH radical. Comparisons with experimental and previous theoretical results are made for each state that has been treated. An understanding of their binding is attempted by means of simple valence bond–Lewis diagrams.

Ab initio investigation of the ground state properties of PO, PO+, and PO−

We have computed accurate potential energy curves of the ground states of the PO(X 2Π), PO+(X 1Σ+) and PO−(X 3Σ−) species by multireference configuration interaction and coupled-cluster methods and have obtained accurate spectroscopic constants for each species. We have also determined the effect of core on the properties above and have obtained the PO complete basis set limit by the multireference method for the equilibrium energy, bond distance, dissociation energy, harmonic frequency, and dipole moment.

States of the CH3C radical conducive to the formation of the C2H3O+ ion

Abstract We have employed multi-reference CI calculations to investigate in some detail the CH 3 C to CH 2 CH isomerization. By following the motion of an H atom along the C–C axis, optimized potential energy curves have been constructed for three low lying states of CH 3 C ( X 2 A ″, A 2 A ′ , a 4 A ″ ) and connected to optimized potential energy curves of correlated CH 2 CH states. The isomerization barrier for each CH 3 C state is estimated from these curves, and the feasibility of the formation of the C 2 H 3 O + ion is discussed. The ab initio energies and geometry changes along the isomerization paths are given, to help visualize the isomerization process.

Conditions conducive to the chemi-ionization reaction O(3P)+CH(X 2Π,a 4Σ−)→HCO+(X 1Σ+)+e−

We have determined the favorable geometries and intermediate HCO states that allow the chemi-ionization reaction O(3P)+CH→HCO+(X 1Σ+)+e− to take place in low-energy collisions, when CH is either in the ground X 2Π or in the first excited a 4Σ− state.

A possible pathway for the formation of the C2H3O+ chemi-ion

Abstract We have verified theoretically the assumption advanced by experimental groups that the CH 3 C radical in its a 4 A 2 excited state is one of the possible precursors of the CH 3 CO + ( X 1 A 1 ) chemi-ion generated in the oxidation of 2-butyne. At the same time we have showed that the ground state of the CH 3 C radical cannot be such a precursor because of the existence of a potential barrier along the reaction coordinate in combination with its fast isomerization to CH 2 CH.

Rotationally inelastic collisions of LiH with He: Quasiclassical dynamics of atom‐rigid rotor trajectories

Rotationally inelastic cross sections for the LiH–He collision system are computed classically using a previously derived ab initio potential energy surface [D. M. Silver, J. Chem. Phys. 72, 6445 (1980)]. The LiH is in its ground vibronic state and is initially taken to be in its j=1 rotational state. The He is in its ground electronic state. The system is treated as an atom‐rigid rotor interaction. The results are compared with previously computed cross sections derived from the same ab initio potential energy surface using the coupled states approximation for quantum mechanical scattering [E. F. Jendrek and M. H. Alexander, J. Chem. Phys. 72, 6452 (1980)]. The theoretical total cross sections are averaged over a temperature distribution and are then compared with experimental measurements of corresponding cross sections for a rotationally resolved LiH beam ( j=1) incident on a He gas target in thermal equilibrium at room temperature [P. J. Dagdigian and B. E. Wilcomb, J. Chem. Phys. 72, 6462 (1980)]. Th...

On the feasibility of chemi-ion formation in the system CH2CH(ã 4A″)+O(3P)

We have investigated theoretically the possibility that the CH2CH(a 4A″) radical can generate the CH2CHO+(X 1A′) ion upon collisions with O(3P). We have concluded that this is very unlikely because the minimum of the ground-state potential-energy surface of the ion is at about the same level as the potential energy of the asymptotic CH2CH(a 4A″)+O(3P) fragments. In addition the Franck–Condon factors should not be favorable because of a drastic change in the geometry of the ion.

The importance of the diabatic channels in the chemi-ionization reaction O(3P)+CH(a 4Σ−)→HCO+(X 1Σ+)+e−

We have investigated the importance of the diabatic channels in the chemi-ionization reaction O(3P)+CH(a 4Σ−)→HCO+(X 1Σ+)+e−. These channels arise due to an avoided crossing along the C–O coordinate at ∼4.7 bohr, between the 2 2Π and 1 2Π adiabatic HCO states as well as between the states that correlate to these two upon bending (4&3 2A′ and 4&3 2A″). We have estimated the nonadiabatic transition probability between these states to be of the order of ∼90%. This indicates that the diabatic channels are indeed very important.

Predissociation lifetimes of the E2Π and F2Π states of CH

Abstract Using the Golden Rule approximation, the predissociation lifetime of the v =0 vibrational level of the CH (E 2 Π) state, due to its strong avoided crossing with the CH (F 2 Π) state, was found to be of the order of τ pre ≈2 ps. This agrees well with the recent rotationally resolved experimental lifetimes. As expected, higher vibrational levels of the E and F states are extremely short-lived, having a τ pre of the order of a few fs.

Predissociation lifetimes of the E 2Π and F 2Π states of CH

Abstract Using the Golden Rule approximation, the predissociation lifetime of the v =0 vibrational level of the CH (E 2 Π) state, due to its strong avoided crossing with the CH (F 2 Π) state, was found to be of the order of τ pre ≈2 ps. This agrees well with the recent rotationally resolved experimental lifetimes. As expected, higher vibrational levels of the E and F states are extremely short-lived, having a τ pre of the order of a few fs.