Knowledge Bank

The $Q1(1)(\nu =1\leftarrow 0,J=1\leftarrow 1)$ rovibrational spectrum of the $J=1$ {ortho}-$H2$ impurities in solid para-$H2$, recorded in our laboratory using a color center laser spectrometer, shows a variety of line widths, spanning nearly two Orders of magnitude. The sharpest line width observed 10 MHz HWHM for 0.2% $o-H2$ at around 4.2 K, belongs to certain {Q} type transitions, which preserve the F, M quantum Dumber in the ground and excited stale resulting in minimum inhomogeneous broadening. Despite the tone burst modulation used in the data recording which distorts the line shape, true line width is derived for Lorentzian line profile. Our results relate to the previous work in microwave region. The broadening mechanism will be discussed including phonon relaxation and inhomogeneous broadening.