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Vertical excitation energies of the C[F.sub.3]Cl molecule are determined from a response function approach with a coupled cluster (CC) reference function in order to examine the absolute photoabsorption oscillator strengths in the molecular-adapted quantum defect orbital formalism (MQDO). The results for the molecular Rydberg transitions have provided better f-values of the isolated Cl atom than the MQDO results.

Equation-of-motion and coupled-cluster methods are used characterizing the electronic structure of C[O.sub.3]. The ground-state equilibrium structures and frequencies are strongly affected by vibronic interactions with low-lying excited states and the vibronic interactions are increased by the Jahn-Teller character of the excited states at [D.sub.3h] geometries.

A study of the reactions of the dicarbon molecules in their electronic ground, ([C.sub.2([X.sup.1][[SIGMA.sub.g].sup.+]]), and first excited state, ([C.sub.2]([a.super.3][Pi.sub.u]) with acetylene, [C.sub.2]H2([X.super.1][[SIGMA.sub.g.sup.+]]) to synthesize the 1,3-butadiynyl radical, ([C.sub.4]H([X.sup.2][SIGMA.sup.+])), plus a hydrogen atom was carried out at six various collision energies ranging from 10.6 to 47.5 kJ[mol.sup. -1) under single collision conditions. It was inferred that in extreme environments like circumstellar envelopes of dying carbons stars and combustion flames, 1, 3-butadiynyl radical can be formed via bimolecular reactions using carbon clusters.

The charge transfer reaction O(sub 2)(super +) + C(sub 9)H(sub 12) -> O(sub 2) + C(sub 9)H(sub 12) was used to prepare highly vibrationally excited n-propylbenzene cations, C(sub 9)H(sub 12). A study was conducted on the subsequent competition between fragmentation of C(sub 9)H(sub 12)(super +) into C(sub 7)H(sub 7)(super +) + C(sub 2)H(sub 5) and stabilization in collisions with N(sub 2) at temperatures in the range 423-603 K and at pressures between 15 and 200 Torr.