Synchrotron-Based Far-Infrared Spectroscopic Investigation and ab Initio Calculations of 3-Oxetanone: Observation and Analysis of the ν₇ Band and the Coriolis Coupled ν₁₆ and ν₂₀ Bands

Abstract

Rotationally resolved vibrational spectra of the four-membered heterocycle 3-oxetanone (c-C(3)H(4)O(2)) have been investigated in the 360-720 cm(-1) region with a resolution of 0.000 959 cm(-1) using synchrotron radiation from the Canadian Light Source. The observed bands correspond to motions best described as C═O deformation out-of-plane (ν(20)) at 399.6 cm(-1), C═O deformation in-plane (ν(16)) at 448.2 cm(-1), and the ring deformation (ν(7)) at 685.0 cm(-1). Infrared ground state combination differences along with previously reported pure rotational transitions were used to obtain the ground state spectroscopic parameters. Band centers, rotational and centrifugal distortion constants for the ν(7), ν(16), and ν(20) vibrational excited states were accurately determined by fitting a total of 10,319 assigned rovibrational transitions in a global analysis. The two adjacent carbonyl deformation bands, ν(16) and ν(20), were found to be mutually perturbed through a first-order a-type Coriolis interaction which was accounted for in the multiband analysis. The band centers agree within 3% of the ab initio estimates using DFT theory.

The ν21 ring puckering mode of 3-oxetanone: A far infrared spectroscopic investigation using synchrotron radiation

“…We recently reported the first rotationally-resolved infrared spectrum of 3-oxetanone in the region 360-720 cm À1 using synchrotron light from the Canadian Light Source (CLS) as the excitation radiation [24]. The observed band centers compared favorably with our ab initio frequency predictions in this particular spectral region.…”

“…The four band origins have been accurately determined to be: 139.549148 (5) [19]. The observed ring puckering fundamental differs by $10 cm À1 from the harmonic frequency calculated using DFT theory (B3LYP/6- 311G++2d3p)) (149 cm À1 ) [24] and by an even greater amount when compared with the value that contains anharmonic corrections derived from second order perturbation theory (158 cm À1 ) [24]. This discrepancy suggests that existing computational procedures are still limited in their ability to accurately model such low frequency vibrations.…”

“…For the fundamental band, we used the estimated band origin from the survey spectrum and the ground state constants previously determined from our recent far infrared study of three higher frequency vibrations [24] and earlier microwave work [22] to simulate the ring puckering band structure. Once the patterns observed in the Loomis-Wood plot were identified based on comparison with the simulation, ground state combination differences were used to confirm the quantum number assignment of transitions within the fundamental band.…”

“…A global fit consisting of all 9165 assigned rovibrational transitions from the m 21 fundamental and the first three hotbands was performed in Pickett's SPFIT program using Watson's A-reduced Hamiltonian, I r -representation [27] with the ground state spectroscopic constants held fixed to the values previously reported [24]. The rms error of the simultaneous four state fit was 0.000098 cm À1 and the complete set of fitted spectroscopic constants is provided in Table 1.…”

“…The highly congested spectrum includes transitions due to the fundamental and first three hotbands of this vibration. A global analysis of 9165 separate infrared transitions was performed by fixing the ground state parameters to those previously determined [24]. The resulting spectroscopic parameters provide accurate and precise characterization of the v = 1 through v = 4 ring puckering states via the rotational and centrifugal distortion constants.…”