The high-resolution FIR-spectrum of oxetane

Oxetane, (CH2)(3)O, is a four-membered ring molecule exhibiting a large-amp litude ring-puckering motion. In order to analyze this vibration we recorde d a rotationally resolved far infrared-spectrum between 50 and 145 cm(-1). Since the spectrum was not resolved at room temperature, the sample was coo led to 203 K. The temperature change has a strong effect on the spectrum. T he spectrum consists of c-type rotation-puckering transitions. We assigned 1108 lines belonging to (q)Q(Kc) and R-q(Kc), subbranches of the fundamenta l band. An A-reduced Watson Hamiltonian was used to perform a combined fit of the assigned transitions together with pure rotational transitions taken from the literature. The band origin of the fundamental ring-puckering tra nsition was determined to be 52.920327(11) cm(-1). In addition, precise rot ational constants and centrifugal distortion parameters up to the sixth ord er for the ground state of the ring-puckering motion in oxetane were obtain ed. On the basis of these spectroscopic constants a Fortrat diagram was cal culated. This diagram shows the asymmetry splitting of the (q)Q(Kc) subbran ches, especially near the origin of the fundamental band, and together with the assigned transitions, provides the basis for high-resolution laborator y or interstellar Terahertz spectroscopy of this molecule. (C) 2001 Elsevie r Science B.V. All rights reserved.