Document Type

Dissertation

Date of Award

1977

Keywords

Molecular spectra

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

K. Keith Innes

Second Advisor

Stanley K. Madan

Third Advisor

Daniel D. Konowalow

Abstract

Seven type C bands of the 3700 A Ã1B1-X̃1A1 system of pyridazine (1,2-diazine) have been analyzed by rotational band contour analysis. The rotational constants, in either the upper or lower state, of each band were adjusted until the simulated contour reproduced the following features of the observed rotational contour: (1) the rotational peak positions, (2) the full width at half maximum of the Q-branch and (3) the onset of rotational structure disintegration. The derived moments of inertia for the v′=0 level of the Ã1B1 state indicate that the pyridazine ring is elongated along the axis parallel to the N-N bond in this state as compared to the ground state. Two indistinguishable simulated contours, which differ only by an interchange of directions of the two in-plane axes of inertia of the excited state molecule, preclude precise determination of the extent of this ring elongation. A similar elongation of the pyridazine ring is found to result when one quantum of 𝜈6a is excited in the X̃1A1 ground state. On the basis of the present and all other available experimental evidence, a band only 373 cm-1 above the 0-0 band of the Ã-X̃ system is identified tentatively as the 0-0 band of the B̃1B1-X̃1A1 system.

The observed diffuse contour for the band corresponding to the 1393 A Rydberg transition of the trans-1,3-butadiene-d0 molecule also has been simulated by rotational band contour analysis. The following features, observed for samples at both -80°C and +25°C, were reproduced in the simulated contour: (1) the full width at half maximum, (2) the ratio of the intensity of a shoulder, which is found on the high frequency side of the band, to that of the band maximum, (3) the band maximum to shoulder separation and (4) the steepness of the high frequency edge of the band. This band is shown to be a type C band so that the transition moment must lie perpendicular to the plane of the molecule. The Rydberg transition is therefore assigned as a 1Au-1Ag transition. This represents the first direct determination of the polarization of an electronic transition of a polyene molecule. The v′=0 level of the excited state is shown to have an average lifetime of 3x10-13 sec. Derived moments of inertia indicate that the excited state is perturbed by a nearby electronic state.

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