A spectroscopic study of CaOCH3 using the pump/probe microwave and the molecular beam/optical Stark techniques

Abstract

The Stark effect on the R (0,0.5) ( = 17682.9251 cm ) and P (0,1.5) ( = 17682.1966 cm ) branch features of the (0,0) band system of calcium methoxide, CaOCH , was measured and analyzed to give the permanent electronic dipole moments, , of 1.58(8)D and 1.21(5)D for the and states, respectively. The dipole moments are compared with other monovalent calcium compounds and those predicted from a simple electrostatic model. Pure rotational transitions in the state were recorded using the pump/probe microwave-optical double resonance technique. The proton magnetic hyperfine splitting pattern confirms that the symmetry of the ground electronic state is C . The determined small negative value for the Fermi contact parameter (a = -0.419 MHz) is interpreted in terms of spin polarization effects. The determined spin-rotational parameter (( = 12.45 MHz ) is compared to that of other monovalent calcium compounds and interpreted in terms of the proposed state distribution.

Geometry of the CaOCH3 radical from isotope effects in the transition

“…We removed the ground-state distortion coefficient D K which previously had been fixed [1] at a value determined with microwave accuracy for CaOCH 3 [6], and whose contribution to all line wavenumbers was less than the experimental uncertainty.…”

“…In the first iteration, the data for each isotopomer were fitted to the same set of upper-state parameters considered in our first paper [1]. The ground-state constants for the main isotopomer CaO 12 CH 3 were fixed at the values used in our original study [1], which had been obtained with microwave accuracy [6]. All other parameters were optimized, and the results examined for isotopic consistency.…”

The A2E–X2A1 System of CaOCH3

“…A standard nonlinear least-squares optimization procedure (Levenberg-Marquardt) was used to fit the data. We initially assigned three subbands with K = 0, ±1 and, fixing the ground state constants to those of Namiki et al (12), fitted the data to derive an initial set of upper state constants. These were then used to create a synthetic spectrum as described below and to calculate line positions for additional values of K .…”

“…Calcium species have drawn particular attention: CaOH should be abundant in circumstellar envelopes (7) and the question of its electric dipole moment has been the subject of both experimental (8) and theoretical (9) investigations. Marked similarities between spectra of linear CaOH and the Ca monohalides invited extension of these studies to CaR compounds of lower symmetries, in order to understand their electronic structure and bonding: for instance CaNH 2 (10) for C 2v , CaCH 3 (11) and CaOCH 3 (12,13) for C 3v . The C 3v species are of particular interest for Jahn-Teller studies, as shown in a recent review (14), because they give access to degenerate E electronic states where such vibronic interaction can take place.…”

“…The A 2 E-X 2 A 1 system of CaCH 3 near 680 nm has been studied in Ref. (12) by optical Stark spectroscopy, while in Ref. (13) the B 2 A 1 -X 2 A 1 system of CaOCH 3 at 565 nm was analyzed by laser excitation spectroscopy, in both cases at a rotational resolution.…”