The most far-reaching result to come from the study of interstellar molecules has been the recognition of a new class of galactic structures - molecular clouds. These clouds appear to contain most of the mass of the interstellar medium and are the objects from which new stars are formed. Thus, a prerequisite for any understanding of the star formation process is a knowledge of the physical and dynamical conditions in molecular clouds.

The 91.5 cm telescope of NASA's Kuiper Airborne Observatory has been used, in conjunction with an InSb heterodyne receiver, to detect the J = 4-3 submillimeter transition of CO (461 GHz) and the 414−321 transition of H2O (380 GHz). The water emission was detected from the Orion “plateau” region.

The upper half of the frequency band lying between the atmospheric water lines at 183 and 323 GHz is virtually unexplored by spectroscopists of interstellar matter. The only published observations are those of Huggins et al. (1979) who detected the J=3-2 lines of HCN, HNC, and HCO+ in the Orion A molecular cloud (OMC-1). We report here the results of extensive observations made in March and April of 1979 with a University of California (Berkeley) receiver on the Texas 4.9-m antenna.

Sensitive measurements have been made of the profiles of various molecular lines in the direction of the BN/KL infrared complex in Orion. Similar line shapes are found for the high velocity wings (“plateau”) of most lines observed. The position of the high velocity source (HVS) was found in SO and HCO+ relative to the SiO maser. A search for HV emission in other sources was unsuccessful.

Observations at both millimeter and infrared wavelengths reveal energetic activity within the core of the Orion molecular cloud in the vicinity of the KL-BN cluster. New observations of the high velocity CO emission at 2.6-mm with improved angular resolution (HPBW = 44″) show that the source diameter averages 4 × 1017 cm and the center of mass is displaced 10-12″ north of the Kleinmann-Low nebula to a position close to the Becklin-Neugebauer object. The total mass of high velocity gas in the core region is ∼10 M⊙ (assuming 10% of the carbon is in CO); the present kinetic energy is 4 × 1047 ergs. Further evidence that BN may be the ultimate source of this energy is provided by high resolution infrared spectra which show both ionized and high temperature (Tk ≳ 3000 K) neutral gas in this source. CO bandhead emission (v = 2 → 0, 3 → 1, and 4 → 2) seen in BN is thought to arise from collisional excitation at high temperatures in a very dense (nH > 1010 cm−3) region only 1 AU in size. And high spectral resolution profiles of the Br α and γ recombination lines show that the HII region previously detected in BN apparently has motions over 100 km s−1.

The distributions of the H13CN, H12CN and H12CO+ J =1-0 lines have been mapped with 20″ spacing towards the Orion A molecular cloud using the new Onsala 20 m millimeter wave telescope equipped with a room temperature mixer. The aperture and main beam efficiencies are about 49 and 65% and the half power beam width is ∼ 43″. The absolute pointing accuracy is estimated to be better than 5″ rms in the Orion elevation range.

Observations of millimeter wavelength emission lines at the highest possible angular resolution are necessary to reveal the energetics and dynamics in compact regions of star formation activity. Lunar occultations of molecular clouds provide a means for obtaining angular resolution that is much better than that possible with a single radio telescope, and make it possible to study in more distant sources features at the same linear scale as those in Orion. We have recently used lunar occultations of the region around two infrared sources embedded in the S255 molecular cloud to determine the angular structure of the CO emission of the surrounding gas, and we have found that this region closely resembles the core of the Orion molecular cloud (Schloerb and Scoville 1980).

We detected new 12CH4 transitions at 21,303 and 94,089 MHz in emission from Orion A, and observed temporal variations of intensity among several velocity components at 76,700 MHz. We also detected an HC5N transition at 21,301 MHz in emission from IRC+10216.

During the past five years, a total of about 180 U-lines has been observed by the author and others in the 70-115 GHz region in the prominent molecular clouds Sgr B2 and Ori (KL). A program to identify the carriers of these lines has been undertaken. A computer code, incorporating nine different centrifugal distortion Hamiltonians, generates spectra of asymmetric rotors from given rotational and centrigugal-distortion constants. Spectra have been computed for ∼550 molecules that are considered potentially interesting astrophysically. Molecules were selected from Landolt-Bornstein Volumes IV (1967) and VI (1974) on Molecular Constants, and from the spectroscopic literature (1973 - present).

The long chain carbon molecules known as the cyanopolyynes (HCnN, n=3,5,7,9) are becoming increasingly more important in astrophysics. At present, the smallest member of the family, cyanoacetylene (HC3N), has been observed in at least 32 sources, and cyanodiacetylene (HC5N) in at least ten. Some 29 transitions of these two molecules have been detected to date, and the number of new sources and new lines is increasing quickly. Although the larger members of the family have not yet been found in sufficient abundance to permit studies in more than a few sources, the fact that they exist at all in detectable amounts is of interest from the standpoint of astrochemistry.

The unsaturated long carbon chain molecules of the type HC2n+1N (with n=1,2..) have the remarkable property of being very stable under a wide variety of different laboratory and interstellar conditions. In fact, they can be synthesized in the laboratory under the action of a radio frequency discharge in a mixture of acetylene, HCCH, and hydrogen cyanide, HCN (Creswell et al. 1977, Winnewisser et al. 1978). Once they are formed they are for example very stable towards temperature changes as well as saturation of the carbon bonds due to hydrogen addition. In the laboratory their chief cause of destruction is polymerization. These experiments were triggered by our observation that in the course of producing hydrogen isocyanide, HNC, (Creswell et al. 1976) by reacting CH3I with N2 in a gas discharge, also small amounts of HC3N were present which clearly requires the joining together of four heavy atoms from different starting molecules.

A map of the NH3 (1,1) emission in Heiles 2 dust cloud, observed with 2.2 arc min. resolution, is presented and compared with that of the J = 9 → 8 transition of HC5N. Although the distribution of both molecules lies on a ridge, there is a marked anti-correlation in the observed antenna temperatures of the two molecules along it. This appears to be best explained as a variation in the relative abundances of the two molecules along the ridge by a factor 8-20 in a distance of 1018 cm.

The Onsala 20 m telescope, equipped with a travelling wave maser (frequency range ∼29-35 GHz; zenith system noise temperature ∼90-160 K) has been used in a search for HC5N (J=12-11 and 13-12) and HC7N (J = 28-27) to a low detection limit. In addition to observations of the Taurus dust clouds TMC1, TMC2 and L1544, the HC5N (J =13-12) transition has been detected at a low level (TA∗ ∼ 0.1 K; p-t-p noise ∼ 0.1 K for a velocity resolution of 0.04 km s-1) in the isolated globule B335. The total HC5N column density estimated from the very narrow line (Δv ∼ 0.2 km s-1) is 6·1011 cm-2. From our non-detection of HC5N in L134N a total column density ≲ 5·1011 cm-2 is deduced.

Emission from SO towards a number of HII regions and molecular clouds with embedded energy sources has been reported by several authors (e.g., Gottlieb et al. 1978; Clark et al. 1978; Wannier and Phillips 1977; and references therein; cf. also Loren et al., 1974; Loren et al. 1975; Lada et al. 1974). Transitions observed include the 45→44, 43→32, 32→21, 23→12, 22→11, 12→11, and 10→01, with the latter (to the ground state) seen only in Sgr B2. Recently Rydbeck et al. (1980) have detected SO in cold, dark clouds and have made the first astronomical measurements of the 10→01 transition in a variety of sources, including the corresponding 34SO line. The latter authors find that the 10→01 transition of SO is an excellent tracer of structure in dark clouds, and they discuss the fractional abundance [SO]/[H2] on the basis of column densities derived from observations of the two isotopic species. They also set limits to the magnetic field strength in dark clouds from the absence of observed Zeeman splitting. We shall provide here additional spectra and information on observing procedures, and shall discuss the rest frequencies for the SO and 34SO 10→01 transitions.

CN(N = 1→0, J = 3/2→1/2) has been searched for toward 8 locations in the Taurus dark cloud complex where NH3 and HC3N and/or HC5N have been observed. CN was detected in TMC1(NH3) and TMC2(cont.) and was probably detected in L1533(NH3) and L1544(NH3). CN appears to be correlated with NH3 and anti-correlated with HC5N and HC3N. It is postulated that NH3 is likely a dominant precursor of CN and HCN but that CN and HCN are probably not important precursors of HC3N and heavier cyanopolyacetylenes.