Knowledge Bank

Laboratory spectra of high rotational transitions in $H2$ are important in astrophysics because they may be observable in hot stellar and interstellar sources, and have already been seen in quadrupole emission from the Orion molecular $cloud.1$ The Orion emission lines are characteristic of an $\sim$ 2000K rotational temperature. Infrared spectra of $H2$ and $D2$ at high temperatures are difficult to obtain in the laboratory because path lengths of hundreds of meters are necessary to observe the quadrupole absorption. Vibration-rotation coefficients obtained from room temperature spectra cannot be extrapolated to the high-J lines observed in Orion to within the accuracies of the astronomical measurements. Prompted by these considerations, we have recorded Raman spectra of high temperature molecular hydrogen and deuterium using a Fourier transform spectrometer. A diffusion flame source burning $H2$ or $D2$ in air was placed at the focal point of a multi-pass $cell.2$ Raman scattering of argon-ion laser light was observed with the l-m Fourier transform spectrometer at Kitt $Peak.3$ The observed pure-rotation spectra of $H2$ and $D2$, and the vibration-rotation spectra of $H2$, contain transitions with higher rotational energy than had been possible to observe previously at room temperature. The transitions in $H2$ extended to J=9-7 and those in $D2$ extended to J=12-10. The rotation-vibration coefficients will be re-examined taking the new transitions into account.