Millimeter-wave observations of molecular lines toward Bok globules and Herbig Ae/Be stars

A sample of 14 small Bok globules and of eight Herbig Ae/Be stars has been observed in the molecular rotational lines of HCO+, HCN, HNC, N2H+, and C2H at 3 mm wavelength. The observational results have been used together with a pseudo-time-dependent chemical model to study the evolution of a molecul ar cloud toward the formation of a low-mass star. The new chemical and phys ical scenario that is inferred from the molecular line data is discussed in relation with the existing literature data obtained from infrared to far-i nfrared data.