Accuracy limits for simple molecular absorption based wavelength references

We present limitations on the characterization and use of molecular absorption lines for wavelength calibration purposes. These limits assume a Doppler and pressure-broadened absorption spectrum obtained by transmitting light through a simple gas cell. Attempting to define the line centers to ever-higher accuracy reveals limits associated with effects of cell pressure uncertainty, weak features in the spectrum, increasing complexity in the line profile model, and accuracy limits of wavelength meters.