High-resolution infrared studies of the ν10, ν11, ν14, and ν18 levels of [1.1.1]propellane

Abstract

This paper is a continuation of earlier work in which the high resolution infrared spectrum of [1.1.1]propellane was measured and its k and l structure resolved for the first time. Here we present results from an analysis of more than 16000 transitions involving three fundamental bands ν10(E′-A1′),ν11(E′-A1′), ν14(A2″-A1′) and two difference bands (ν10–ν18) (E′−E″) and (ν11−ν18) (E′−E″). Additional information about ν18 was also obtained from the difference band (ν15+ν18)−ν18 (E′−E″) and the binary combination band (ν15+ν18) (E′-A1′). Through the use of the ground state constants reported in an earlier paper [1], rovibrational constants have been determined for all the vibrational states involved in these bands. The rovibrational parameters for the ν18 (E″) state were obtained from combination–differences and showed no need to include interactions with other states. The ν10 (E′) state analysis was also straight-forward, with only a weak Coriolis interaction with the levels of the ν14(A2″) state. The latter levels are much more affected by a strong Coriolis interaction with the levels of the nearby ν11 (E′) state and also by a small but significant interaction with another state, presumably the ν16 (E″) state, that is not directly observed. Gaussian calculations (B3LYP/cc-pVTZ) computed at the anharmonic level aided the analyses by providing initial values for many of the parameters. These theoretical results generally compare favorably with the final parameter values deduced from the spectral analyses. Finally, evidence was obtained for several level crossings between the rotational levels of the ν11 and ν14 states and, using a weak coupling term corresponding to a Δk=±5, Δl=∓1 matrix element, it was possible to find transitions from the ground state that, combined with transitions to the same upper state, give a value of C0=0.1936515(4)cm−1. This result, combined with the value of B0=0.28755833(14)cm−1 reported earlier [1], yields a value of 1.586277(3)Ǻ for the length of the novel axial CC bond in propellane.