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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−1region 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.

Extensive new high-temperature, high-resolution FTIR emission spectroscopy measurements for the five common isotopomers of GeO are combined with previous diode laser and microwave measurements in combined isotopomer analyses. New Dunham expansion parameters and an accurate analytical potential energy function are determined for the groundX1Σ+state.

A new way of representing vibration–rotation term values for multiple isotopomers of a given electronic state of a diatomic molecule is presented which resolves problems associated with the way the conventional combined isotopomer expansion represents the atomic mass-dependent JWKB and Born–Oppenheimer breakdown correction terms. Its application to infrared and microwave data for HF and DF yields new Dunham expansion coefficients and Born–Oppenheimer breakdown correction terms for this species. This procedure is implemented in a generally available computer program for fitting to various types of data involving one or several electronic states of multiple isotopomers of a diatomic molecule.

This paper describes a procedure for optimal rounding of parameters determined from a linear or nonlinear least-squres fit in order to minimize the number of digits which must be quoted while ensuring that the resulting rounded constants can predict the input data with no significant loss of precision. Related problems concerning nonlinear least-squares convergence and taking account of model dependence of fitted or predicted parameters are also addressed. The recommended rounding procedure is illustrated by applications to electronic band data for theA–Xsystem of I2and to infrared and microwave data for HF (yielding optimal new Dunham expansion coefficients for ground state HF). An automated version of this sequential rounding procedure has been incorporated in a general subroutine for performing linear or nonlinear least-squares fits.