Fine structure formation in the electronic spectra of larger molecules

FTIR and diode laser spectroscopy of isobutylene: Analysis of the rotational structure in the v28 fundamental band

“…Within the Watson/Gora approximation, K a can be considered a nearly degenerate quantum number label and Eq. (2) would suggest the rotational levels are actually independent of K a [16]. Nevertheless, the selection rules DK c = 0 and DK a = ±1 must be taken into account.…”

“…Under such circumstances, there are a set of relatively simple energy expressions in A, B, and C which can be used to fit spectra (see for example Gordy and Cook [21]). There are also limiting sets of circumstances, such as the high J, low K c and high J, low K a approximations, under which an asymmetric rotor might exhibit symmetric top behavior [15,16,11].…”

“…This mathematical treatment produced a power series expression, in [J(J + 1)] 1/2 , for the rotational energy levels of a rigid asymmetric top which proved remarkably accurate in the limit of high J, low K a . A short time later, John Brown extended this treatment to include the analogous high J, low K c set of energy levels [16]. Although these energy level expressions are apparently not well known, the asymptotic formula have been successfully applied and used to analyze regularities in the rotational spectra of several light molecules [15], as well as the rovibronic structure in certain bands of oxalic acid [17].…”