Abstract
T he jet-cooled fluorescence excitation spectra o f cyclopentanone, cyciobutanone and their isotopom ers have been recorded in the 305-335 nm region, respectively. T he electronic band origin for the tw o undeuterated species was determ ined to be 30276 and 30292 cm '1 for the S, (n,7r) electronic excited states, respectively. M ore than one hundred fluorescence bands w ere assigned for each cyclopentanone species, and m ore than fifty for each cyciobutanone species. T hese arise prim arily from combinations o f carbonyl m otions and out-of-plane ring modes. E ight bands associated with the excited vibrational states o f the C = 0 out-of-plane wag in the S, electronic states w ere observed for each cyclopentanone isotopom er, and five bands for each cyciobutanone isotopom er. These w ere used to determ ine the one-dimensional potential energies functions fo r th e C = O out-of-plane wagging. T he C = O w agging angle was determ ined to be 2 2 ' , and the b arrier to inversion is 6 7 2 + 1 0 cm '1 for cyclopentanone. These values are 3 9 ' , and 2 1 6 9 + 2 0 cm '1 for cyciobutanone. In the spectrum o f cyclopentanone a progression observed for vn (ring bending) indicates that in the S, state the bent ring conformation lies about 500 c m 1 above the ring-tw isting minimum and corresponds to a saddle point in the two-dim ensional ring-tw isting/ring-bending potential energy surface. Band progressions for vlg (ring tw isting) can be used to estimate the ring-tw isting barriers (the barriers to planarity) for the do and d4 isotopom ers to be 1433 and 1240 cm '1, respectively. F o r the ring-puckering vibration in the S, state o f cyciobutanone the low est three vibrational energy spacings w ere found to be 106, 166 and 185 cm '1 as com pared to values of 35, 57 and 65 cm '1 in the S ground state. Several ring-puckering potential energy functions with varying degrees o f asym m etry are capable o f reproducing the observed results. In all cases, how ever, the v = 0 puckering state lies above any barrier to planarity. A tw o-dim ensional potential function which fits the observed data was also determ ined in term s o f the w agging and puckering coordinates.
Zhang, Jian (1993). Vibrational potential energy functions and conformations of cyclopentanone and cyclobutanone in their electronic excited states. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1521993.