reasonably well with a weak feature found in the electron-energy-loss spectrum at 5.85 eV.7 *A feature in the experimental spectrum at 6.04 eV has been previously assigned as the 2*BU state.7 Given the error in our calculated ionization potential, it is unrealistic to attempt to choose between these two features based on the calculated results.One question which remains unanswered by the present study is the cause of the seeming disappearance of the 2'Ag state in the gas-phase fluorescence spectrum. Our results indicate that in relaxed excited-state geometries the 2*Ag state is found to lie significantly below the l'Bu state. Since the calculations are performed on the isolated molecule, the cause of this discrepancy remains unresolved. Clearly further work is required to answer this question. V. ConclusionResults are presented from ab initio Cl calculations for several low-lying excited states of «//-Zranj-octatetraene. In a vertical transition from the ground state the lowest singlet excited state is found to be of 'Bu symmetry. This state is essentially valencelike.The second excited singlet state, is a 2*Ag state at the ground-state geometry, the zeroth-order description of which is multiconfigurational and can be identified with the so-called "doubly excited" state found in long-chain polyenes. However, application of a correction for the 2*Ag state based on the estimated 0-0 transition energy makes the l'Bu and 2'Ag states essentially degenerate at the ground-state geometry. Relaxation of the excited-state geometries leads to the 2*Ag state having the lowest 0-0 transition energy. Reasonable agreement is found with experiment where comparisons can be made, and we predict that the 2'BU state is of 3p* Rydberg character and lies near 5.65 eV.

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The interaction of the CO2 molecule with nickel atoms was studied by using matrix isolation spectroscopy and density functional theory. In argon dilute matrices, no reaction occurs, even after annealing the deposit. In neat CO2 matrices, it is shown that carbon dioxide forms a 1:1 complex with nickel which is characterized by its UV−visible and FTIR absorptions, including isotopically labeled species. Theory predicts the side-on coordination mode to be the most stable. The binding energy of the side-on Ni(CO2) complex is estimated to be 18 kcal/mol. The calculated OCO angle is 145°, which is quite a large value compared to those encountered in other known CO2 complexes. In dinitrogen matrices, the yield of CO2 complexation is considerably enhanced relative to that in argon dilute and neat CO2 matrices, which is attributed to the formation of unsaturated Ni(N2) n complexes prior to CO2 coordination. The CO2 binding energies calculated for the Ni(CO2)(N2) n (n = 1, 2) complexes (respectively 32 and 4 kcal/mol) suggest that CO2 probably coordinates to the Ni(N2) complex. This is a very interesting result, owing to the fact that CO2 does not react with nickel atoms in dilute argon matrices.

The Ar+ laser-excited spectrum of matrix-isolated V2 consists of a resonance Raman progression with ωe=537.5 cm−1 and ωexe=4.2 cm−1. With increasing laser power several members of an anti-Stokes progression and sequence components on both Stokes and anti-Stokes members of this progression were observed and attributed to transitions originating from vibrationally excited stated populated as a result of laser irradiation. A second system with ωe=508 and ωexe=3.3 cm−1 also grew in with increasing laser power and 496.5 nm excitation. This was interpreted as a resonance Raman progression within an electronically excited state (A) of V2. The electronic resonance Raman spectrum corresponding to the A→X transition was also observed as well as one to another low-lying electronic excited state. The v′=0 level of state A was found to lie 1860 cm−1 above the v″=0 level of the ground state. The multiple photon nature of the transitions discussed above was determined by performing laser power measurements. The resonance Raman spectrum of Ti2 was excited with HeNe and dye laser illumination in solid argon matrices containing titanium. As with V2, laser irradiation populated excited vibrational states of the ground state, producing an anti-stokes, resonance Raman progression. Isotopic components of Ti2 were resolvable under high resolution, corroborating the assignment. A discussion of multiple bonding in transition metal dimers is presented which shows that the contribution of bonds originating from the atomic d orbitals do not always contribute uniformly to the metal–metal force constant. Hence the formal bond order is not always a good gauge of the bond strength of a transition metal dimer.