Knowledge Bank

Unless very careful and skillful precautions are taken, measurement of collision-induced line shifts using a tunable diode laser can be unreliable on account of the commonly encountered jitter and instability in the laser signal. However, when lines belonging to different molecules appear in the spectral scan as neighbors (reference lines) that do not interfere with the absorption of the observed line, as in the case of the three methanes and N2O, accurate line shift measurement is feasible. Using separate absorption cells for the reference and sample gases and placing them in series, we have been able to measure the pressure-induced shifts of the rotational lines of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4,\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH4,\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH3D$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}N2O$ located between 1265 and $1275cm-1$. The temperature dependence of the shifts is also presented for collisions of the absorbers with $H2,He,Ar,N2,O$, and air.