“Forbidden” transitions of AsH₃ molecule recorded by RAD spectrometer.
The spectrometer sensitivity can be calculated using the line maximum absorption coefficients (shown above) and the recording signal to noise ratio as:

For more details see paper [Ref. 1 (1987)].

Investigation of the 22-GHz atmospheric diagnostic water vapor line using RAD spectrometer. Three hundred experimental spectra (lock-in time constant is 0.5 s) of the mixture of water vapor with argon are shown by grey curves. Averaged spectrum is shown by solid black curve. Pure rotational transition 5₃₂-5₃₃ of HDO molecule in natural abundance is seen in the upper line wing near 22.307 GHz (shown in the inset). Evaluated sensitivity of the spectrometer is 2×10^-10 cm^-1 [Ref. 1 (2018)].