Abstract

To better understand how the HII regions can affect their surrounding molecular clouds we have studied the molecular distribution towards three compact HII regions associated with IRAS sources (08140-3559, 09014-4736, and 09026-4842) by means of the observations of (CO)-C-12, (CO)-C-13, and (CO)-O-18 molecules in the J = 3-2 transition with the APEX telescope. In two cases, we show evidence of possible disruption of the molecular clouds and increasing turbulence towards the diffuse Ha emissions, which could be due to the ionizing front. We find 11 clumps towards the IRAS sources either nearby or surrounding the HII regions. Their parameters, such as the optical depths, column densities, masses, and [(CO)-C-13/(CO)-O-18] abundances, were calculated assuming LTE conditions. We discuss the behaviour of such parameters and we have found that the [(CO)-C-13/C18O] abundances in the IRAS sources associated with a diffuse Ha emission are higher than the abundances in regions where no Ha emission is detected, indicating that such a parameter could be affected by the UV field coming from HII region. We also discuss the rise of the average [H-2/(CO)-C-13] and [H-2/(CO)-O-18] abundances in the IRAS sources which show evidence of disruption of molecular clouds by the expansion of the HII regions. With these average abundances, we estimate the LTE total mass of each clump and compare them with the virial mass to discuss whether our clumps are gravitationally stable.