Fourier Transform Spectroscopy of the A′1Π–X1Σ+ System of CaO

Abstract

The A′1Π–X1Σ+ near-infrared system of CaO was observed for the first time at high resolution using a Fourier transform spectrometer. The A′1Π–X1Σ+ chemiluminescence was excited in a Ca + N2O flame produced in a Broida-type oven. More than 3000 rotational lines, classified into 19 bands involving the A′1Π 0 ≤ v′ ≤ 3 and the X1Σ+ 1 ≤ v" ≤ 7 vibrational levels were measured in the 4000–10000 cm−1 region with a precision of 0.005 cm−1. The X1Σ+ (v = 0, 1) millimeter-wave and X1Σ+ (v = 0–3) infrared data available in the literature were merged with our new electronic data in order to obtain improved Dunham constants for the ground state of CaO. Very peculiar perturbations are observed in the higher vibrational levels of the A′1Π state, so the upper levels of transitions with v′ = 2 and 3 were represented by term values in our least-squares analysis. The interaction of the A′1Π (v ≥ 2) levels with the nearby b3Σ+ (v–2) levels has been detected. An extended set of A′1Π (v = 0–3) data has been obtained which is suitable for use in a future multistate deperturbation analysis of the a3Π ∼ A′1Π ∼ b3Σ+ ∼ A1Σ+ complex of excited states. The new near-infrared spectra of the A′1Π–X1Σ+ transition of CaO also permits the first direct high-resolution linkage between the orange and green systems and the near-infrared bands.