Far-infrared spectrum and ring-puckering of 3-cyclopenten-1-one

Effects of π* ← n Excitation in 4-Cyclopentene-1,3-Dione

“…The 19 2 2 bands were observed, the 14 sequence intervals increase with v. It can also be seen in Fig. 7 that the 19 sequence intervals vary with the 10 nЉ nЈ band to which they are attached, increasing with (nЈ Ϫ nЉ).…”

“…7 that the 19 sequence intervals vary with the 10 nЉ nЈ band to which they are attached, increasing with (nЈ Ϫ nЉ). It follows that, in both electronic states, 19 increases by about 1.7 cm Ϫ1 for each quantum of 10 with which it is combined. Variation of the 19 sequence interval with modes other than 10 is small and irregular.…”

“…They are much less distinct than neighboring sharp bands, but, given their broader contours, their intrinsic intensity may not be much lower. The band at ⌬ ϭ Ϫ239 cm Ϫ1 corresponds to the a 2 19 , but this cannot be taken as a precise value for the gas-phase fundamental. A lower value of 90 cm Ϫ1 was estimated for Љ 19 in the microwave study (12).…”

“…Other broadbands can be assigned as 19 sequences attached to the parent bands described above, or to combinations with, Ј 10 .…”

“…Successive bands within a sequence are only slightly diminished in intensity, and typically four members are observed. Because of its strength, this sequence is assigned to the b 1 ring-puckering mode 19 , the lowest wavenumber vibration, with a ground state fundamental of approximately 100 cm Ϫ1 . A second, weaker sequence, with separations of approximately 65 cm Ϫ1 , is assigned to the a 2 ring-twisting mode 14 , the second-lowest wavenumber vibration.…”