A Four-Parameter Spectrally-Universal Line Shape Function

A 3-parameter lineshape function, defined by convolving the Gross and Doppler lineshape functions, was previously proposed as a spectrally universal form. It reduces to the Gross lineshape at microwave and longer wavelengths, and transitions to the Voigt lineshape in the infrared. Unfortunately, the Gross lineshape function is known to not capture the asymmetry of the true microwave lineshape as well as the Weiskopf form. Here, a Center-Shift at Half-Width parameter is introduced to create a modified-Gross lineshape function applicable in the microwave. Its spectral convolution with the Doppler lineshape is demonstrated to provide a 4-parameter lineshape function accurate for the entire ultraviolet to radio wave spectral range.