Spectrum of azulene. IV. Rotational analysis of the 0-0 band of the 3500 Ǻ transition

Abstract

The bands of the 3500 Ǻ transition of azulene-do and azulene-ds show two unequal peaks 2.3 cm-l apart, followed by closely spaced fine structure. These bands have been analysed as type A bands of a planar, prolate asymmetric top. Rotational constants for both molecules in the excited state have been determined. The fine structure is due to multiple line coincidences in the high-J, low-K region of the qP branch. To each multiple line can be attributed a running number n = J+m, where m = J-K-1. Given sufficient resolving power, such "lines" should be rather commonly observed in type A and type B bands of large, planar, prolate molecules.

Rotational assignments in electronic spectra of large asymmetric rotor molecules

“…An example of an observed type A band which illustrates the sharp peak arising from these qrR transitions is the intense peak to high wavenumber of the origin in the 0-0 band of the 3500 3, system of azulene [7]. The recognition of such a feature in a type A band may well be of greater value for evaluation of AC than in a type B band since the position of the band origin in a type A band can often be readily found in the observed contour (see for example type A contours of azulene [7] and benzoquinone [10]).…”

“…The recognition of such a feature in a type A band may well be of greater value for evaluation of AC than in a type B band since the position of the band origin in a type A band can often be readily found in the observed contour (see for example type A contours of azulene [7] and benzoquinone [10]). …”

“…Each branch therefore can be labelled by its value of n (n = J + m). The multiple line coincidences responsible for the fine structure under discussion here were briefly mentioned by McHugh et al [7] who gave the equation for the transition wavenumbers (equation (9) …”

“…From an equation derived by Gora [8], McHugh et aL [7] have obtained a simple expression for the low Ka and high J energy levels of planar prelate asymmetric rotors:…”

“…Assignments of computed features (table 2, [2]) are +2.37, m=2; +2.12, m=3; +1.90, m=4; +1.67, m=5; +1.47, m=6; +1-25, m=7. The approximate positions of these heads can be calculated with the energy level formula of McHugh et al [7] given in equation (1), with Am= + 1, An= + 1. In particular the J value at reversal is quite accurately given by equation (2), that is the same equation as for the low Ka R branches.…”