The rotational contour of the 0-0 band of the 1A"(n~*)-IA" system of s-trans acrolein has been analysed. Interpretation of the excited state rotational constants shows that the changes in angles CCC and CCO, if assumed to be equal, are between +3 ~ and +4 ~ over a large range of Arc=c, Arc=o and Arc-c and, if Arcffic and Arc=o are assumed equal, then Arc-c ~ -Arc=c over a large range.Weaker bands, to low wavenumber of the 1A"(nTr*)-lA' system of s-trans acrolein, are sorted by their temperature dependence and characteristic contours into two systems: the 4120 k system is the 8A"(nTr"r system of s-trans acrolein while the 4060 A system is shown to be the 1A"(n~r*)-IA" system of s-cis (or possibly gauche) acrolein. Evidence for this has been obtained from ground state vibration wavenumbers, rotational band contours and temperature effects.Temperature dependence of the intensity of bands has been used to show that the separation of the s-trans and s-cis zero-point levels in the ground electronic state is 770 _+ 40 cm -1 and that the torsional vibration wavenumber of the s-cis form is 230 _+ 40 cm -1 in this electronic state. It is estimated that there is about 4 per cent ofs-cis acrolein at 20~ 7 per cent at 100~ and 12 per cent at 200~
A vibrational analysis of the 370 nm system of tropolone (--OH) and (--OD) has shown that pairs of bands, resembling the O0 ~ and H11 bands (where vii is the internal hydrogen-bonding vibration), dominate the spectrum. Pairs built on O0 ~ and HI 1 and due to the excitation of totally symmetric vibrations in the ground or excited electronic state are well-behaved in the sense that their separations and rotational contours are very similar to those of O0 ~ and H11. About seven sequence intervals, in vibrations other than va, have also been identified and it is observed that rotational contours of ZllHx 1 bands in five sequence-forming vibrations Z are quite strongly perturbed (four of them in a very similar way) while the corresponding Z~ 1 bands are unperturbed.It is concluded that the unusual nature of va is in some way responsible for the rotational perturbations and also for the very unusual behaviour of some quite intense vibronic bands in the region 290-540 cm -1 to high wavenumber of the O0 ~ band : however, the evidence is only circumstantial.
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