The star formation in molecular clouds is inefficient .
The ionizing EUV radiation ( h \nu \geq 13.6 eV ) from young clusters has been considered as a primary feedback effect to limit the star formation efficiency ( SFE ) .
We here focus on effects of the stellar FUV radiation ( 6 eV \leq h \nu \leq 13.6 eV ) during the cloud disruption stage .
The FUV radiation may further reduce the SFE via photoelectric heating , and it also affects the chemical states of the gas that is not converted to stars ( `` cloud remnants '' ) via photodissociation of molecules .
We have developed a one-dimensional semi-analytic model which follows the evolution of both the thermal and chemical structure of a photodissociation region ( PDR ) during the dynamical expansion of an HII region .
We investigate how the FUV feedback limits the SFE , supposing that the star formation is quenched in the PDR where the temperature is above a threshold value ( e.g. , 100K ) .
Our model predicts that the FUV feedback contributes to reduce the SFEs for the massive ( M _ { cl } \gtrsim 10 ^ { 5 } ~ { } M _ { \odot } ) clouds with the low surface densities ( \Sigma _ { cl } \lesssim 100 ~ { } { M } _ { \odot } { pc } ^ { -2 } ) .
Moreover , we show that a large part of the H _ { 2 } molecular gas contained in the cloud remnants should be `` CO-dark '' under the FUV feedback for a wide range of cloud properties .
Therefore , the dispersed molecular clouds are potential factories of the CO-dark gas , which returns into the cycle of the interstellar medium .