A new program for the assignment and fitting of dense rotational spectra based on spectral progressions: Application to the microwave spectrum of pivalic anhydride

Abstract

A new computerized package for the rapid processing and analysis of dense rotational spectra is described. The package is based on the automated identification of user-specified spectral progressions and interacts with the operator through a simple graphical user interface. In addition to containing an algorithm for obtaining spectral assignments, the package includes a peak-finder with adjustable baseline drift compensation, seamless interfacing with Pickett’s SPFIT and SPCAT programs, and a number of visualization features. The utility of the program is illustrated through its application to the analysis of new spectra of pivalic anhydride, (CH3)3CCOOCOC(CH3)3. Spectra of the parent, as well as all isotopologues with single heavy-atom substitution, are reported, as are calculations for the parent species at the M06-2X/6-311++G(3df,3pd) level of theory. The central oxygen atom is poorly located due to its proximity to the center of mass of the molecule, but a Kraitchman analysis of the fitted rotational constants otherwise provides a detailed structural characterization of the heavy-atom frame. The two carbonyl groups are not coplanar, but rather form a dihedral angle of 53.9(39) deg.