Context :

Aims : We are presenting here a follow-up study of the molecular gas and dust in the environs of the star forming region NGC 3503 .
This study aims at dealing with the interaction of the H ii region NGC 3503 with its parental molecular cloud , and also with the star formation in the region , that was possibly triggered by the expansion of the ionization front against the parental cloud .

Methods : To analyze the molecular gas we use CO ( J=2 \rightarrow 1 ) , ^ { 13 } CO ( J=2 \rightarrow 1 ) , C ^ { 18 } O ( J=2 \rightarrow 1 ) , and HCN ( J=3 \rightarrow 2 ) line data obtained with the on-the-fly technique from the APEX telescope .
To study the distribution of the dust , we make use of unpublished images at 870 \mu m from the ATLASGAL survey and IRAC-GLIMPSE archival images .
We use public 2MASS and WISE data to search for infrared candidate YSOs in the region .

Results : The new APEX observations allowed the substructure of the molecular gas in the velocity range from \sim - 28 to - 23 km s ^ { -1 } to be imaged in detail .
The morphology of the molecular gas close to the nebula , the location of the PDR , and the shape of radio continuum emission suggest that the ionized gas is expanding against its parental cloud , and confirm the “ champagne flow ” scenario .
We have identified several molecular clumps and determined some of their physical and dynamical properties such as density , excitation temperature , mass , and line width .
Clumps adjacent to the ionization front are expected to be affected by the H ii region , unlike those that are distant to it .
We have compared the physical properties of the two kind of clumps to investigate how the molecular gas has been affected by the H ii region .
Clumps adjacent to the ionization fronts of NGC 3503 and/or the bright rimmed cloud SFO 62 have been heated and compressed by the ionized gas , but their line width is not different to those that are too distant to the ionization fronts .
We identified several candidate YSOs in the region .
Their spatial distribution suggests that stellar formation might have been boosted by the expansion of the nebula .
We discard the “ collect and collapse ” scenario and propose alternative mechanisms such as radiatively driven implosion on pre-existing molecular clumps or small-scale Jeans gravitational instabilities .

Conclusions :