Knowledge Bank

The detection of the $\nu =0\to 0$, S(2) transition of $H2$ in the Orion molecular cloud $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ has prompted a high resolution laboratory study of the pure rotation spectrum of molecular hydrogen. Spectra were recorded with the McMath Fourier Transform Spectrometer at Kitt Peak and were calibrated with respect to 10-micron $CO2$ standard frequencies. Diode laser spectra, of S(2) were also obtained. Preliminary results include an improved measurement of the S(3) line frequency which agrees well with the previous value determined by Reid and McKellar $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$. The new value for the S(2) frequency is significantly different from earlier derivations and, in particular, corresponds to a discrepancy in velocity of 10 $kms-1$ from the value used in interpreting the Orion observations $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$. The use of diode lasers and light emitting diodes as radiation sources for a Fourier transform spectrometer were investigated during this work.