Knowledge Bank

A broad-band room-temperature submillimeter wave spectrum containing approximately 5000 lines of $CH3CHO$ in the region from 165 to 417 GHz has been recorded with the RAD-3 $spectrometer1$in Nizhni Novgorod (formerly Gorky). The sample pressure of approximately 0.1. Torr leads to typical linewidths of 8 MHz, which when combined with some uncertainties in the $SO2$ frequencies used for calibration. Leads to measurement uncertainties of less than 1 MHz for unblended lines. We shall describe the instrument in some detail. Pure rotational transitions with J values from 10 to 20, originating in the torsional ground ($vt=0$) and first excited ($vt=1$) states, can be relatively easily identified using computer programs and molecular parameters determined in earlier $work2-4$. Because of the broad-band spectral coverage of the RAD-3 spectrometer, these assigments can be confirmed in most cases by ``combination-difference loops” of 4 lines, whose frequencies sum to values less than $4$ Times the 1 MHz measurement precision. The goal of the present work is not a study of $Vt=0$ and 1 transition, however, but involves instead a search for lines originating in higher ($vt=2$ or 3) torsional states. We shall report on our attempts to find such lines in this RAD-3 spectrum.