Microwave Spectrum, Dipole Moment, and Ring-Puckering Vibration of β-Propiolactone

Abstract

The microwave spectrum of β-propiolactone has been observed in the vibrational ground state and in the first four excited states of the ring-puckering vibrational mode. The variation of the rotational constants with vibrational quantum number and the relative intensities of the observed vibrational satellites indicate that the vibration is essentially harmonic with ν0=160 cm−1 and with no appreciable barrier at the planar configuration. The dipole moment is 4.17±0.03 D, with μa=3.67±0.03 D, μb=1.99±0.02 D, and μc=0 in both the ground and first excited states.

A combined ab initio, Fourier transform microwave and Fourier transform infrared spectroscopic investigation of β-propiolactone: The ν8 and ν12 bands

“…The spectroscopic constants obtained in this work provide an excellent description of the observed rotational spectrum as many of the m obs-calc residuals reported in Table 1 are smaller than ±1 kHz. The parameters determined in this study are compared with those reported earlier by Boone et al [5] in Table 2. The estimated accuracy of the rotational constants in the current study is <3 kHz which is two orders of magnitude lower than that reported previously (±0.2 MHz) and thus, the higher resolution FTMW spectrum has led to an improved determination of the ground state of b-propiolactone.…”

“…Based on the rotational constants of Boone et al [5], a total of 19 microwave transitions have been measured for b-propiolactone between 7 and 21 GHz. Several of these were measured for the first time.…”

“…The structure of b-propiolactone was first determined in the 1950s via electron diffraction [3] techniques and microwave spectroscopy [4,5] to be that of a strained ring such that all 5 heavy atoms are coplanar. The infrared and Raman study of Durig [6] in 1963 provided a comprehensive vibrational analysis of b-propiolactone leading to the assignment of all 21 fundamental frequencies in the liquid and/or gas phase.…”

Ab-initio calculations of the equilibrium geometry of β-propiolactone (2-oxetanone) by the force method

“…The results of the completely optimized ground state structure are given in A-electron diffractions [6]; B-microwave spectroscopy [8,9].…”

“…The dipole moment in the gas phase is 4.17 D [8,9] with components pa = 3.67 f 0.03, = 1.99 f 0.02, pc = 0, where a, b, and c are the principal axes of the inertia tensor, with c perpendicular to the ring plane and a directed along the 01=C2 bond.…”