High-resolution laser excitation spectra of linear triatomic molecules: Analysis of the B2Σ +- X2Σ + system of SrOH and SrOD

Single-mode cw dye laser excitation spectra of the (0, 0 ⁰, 0)-(0, 0 ⁰, 0), (1, 0 ⁰, 0)-(1, 0 ⁰, 0), (0, 1 ¹, 0)-(0, 1 ¹, 0) bands of the 611- to 607-nm system of SrOH and SrOD were observed and assigned. The spectrum is consistent with a ²Σ- ²Σ system where the molecule is linear in both electronic states. The rotational analysis is obtained by measuring P- R separations in the excitation spectrum. A technique which greatly aided in the spectral assignment that utilizes a monochromator as a bandpass filter in obtaining excitation spectra is described. A new spin-rotation constant, γ⁽⁺⁾ - γ^(-), was found necessary to fit the l-type doubling of the (0, 1 ¹, 0) mode in B²Σ ⁺ of SrOH. This new constant is assumed to arise from two ²Σ_{1}/{2} vibronic states, split by Renner-Teller interaction, of the (0, 1 ¹, 0) mode of A²Π. From a perturbation treatment of this electronic interaction, ∊ω₂ of the (0, 1 ¹, 0) mode of A²Π was found to be 14 cm ^-1. The linear structure of SrOH and SrOD in both electronic states is consistent with the model, in the one-electron approximation, in that the transition involves the promotion of the unpaired 5 s to the 5 p orbital localized on the strontium.