VVW Flag: Apply Van Vleck-Weisskopf Correction to Lineshapes
Apply VVW correction term to line-by-line calculations
(unless already calculated using VVW lineshape - see *SHP
The Van Vleck Weisskopf lineshape is generally recommended for
calculations in the microwave region (ν <100 cm-1).
The specific Van Vleck Weisskopf lineshape, as specified in the
*SHP section, is a more accurate theoretical
version of the Lorentzian lineshape for this region but if Doppler broadening
is also likely to be significant it is better to apply the VVW correction
to the Voigt lineshape using the VVW Flag than force the full VVW
shape to be used throughout.