Measurements were carried out on the CO J = 3-2 emission line at 345 GHz from a number of translucent and high-latitude molecular clouds, as well as on the J = 2-1 and J = 1-0 lines of both the (C... Show moreMeasurements were carried out on the CO J = 3-2 emission line at 345 GHz from a number of translucent and high-latitude molecular clouds, as well as on the J = 2-1 and J = 1-0 lines of both the (C-12)O and (C-13)O. It is shown that the physical conditions in the high-latitude clouds are very similar to those in the translucent clouds. The densities derived from measured (C-12)O 1-0/3-2 ratios were often found to be higher than those based on the C2 excitation, while densities derived from measured 3-2/(C-13)O 1-0 ratios were similar to those based on C2. Show less
Optical absorption-line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular... Show moreOptical absorption-line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular abundances can be maintained. Results are presented for a survey of absorption lines of interstellar C2, CH, and CN. Detections of CN through the A 2Pi-X 2Sigma(+) (1,O) and (2,O) bands of the red system are reported and compared with observations of the violet system for one line of sight. The population distributions in C2 provide diagnostic information on temperature and density. The measured column densities of the three species can be used to test details of the theory of molecule formation in clouds where photoprocesses still play a significant role. The C2 and CH column densities are strongly correlated with each other and probably also with the H2 column density. In contrast, the CN column densities are found to vary greatly from cloud to cloud. The observations are discussed with reference to detailed theoretical models. Show less
Interstellar absorption lines of the C2 (2-0) Phillips band at 8750 A have been searched for in the spectra of southern stars. Seventeen lines originating from the lowest eight rotational levels... Show moreInterstellar absorption lines of the C2 (2-0) Phillips band at 8750 A have been searched for in the spectra of southern stars. Seventeen lines originating from the lowest eight rotational levels have been detected toward Chi Oph, and eleven lines originating from the lowest five rotational levels toward HD 154368 and 147889. No C2 lines were seen toward HD 149404. A recently developed theory has been used to extract information about the density, temperature or strength of the radiation field in the line-forming interstellar regions from the observed rotational populations. The results are compared with those obtained from other molecular observations. Toward Chi Oph, the interstellar radiation field appears enhanced in the ultraviolet part of the spectrum relative to the infrared part. The C2 data suggest a higher kinetic temperature for the material in front of HD 147889 than is inferred from radio observations. Show less
