Environmental effects on electronic states of small mols. in solid rare gases and in liqs. have severe consequences on the photochem.; examples for valence, Rydberg and ionic states as well as the connection to photochem. dry etching are treated. The repulsive interaction of Rydberg states and the solvation of valence and ionic states are related to spectroscopic properties like gas-to-matrix shifts, Stokes shifts and linewidths. Differential shifts of Rydberg and valence states are illustrated for NO in rare gas matrixes and Fano-type line shapes are attributed to a coherent interaction of broad Rydberg multiphonon continua with valence zero phonon lines. For F2 in Ne a deperturbation of ion-pair and Rydberg states is demonstrated again to originate from a differential shift. For Cl2 the formation of addnl. states due to intermol. charge transfer from the matrix to the guest mols. is obsd. H2O serves as an example to show that repulsive surfaces are strongly modified if the character of the state changes from Rydberg type to valence type with internuclear distance. Information on the dynamics in the femtosecond time scale is derived from intensities in overtone progressions of resonance Raman spectra and it is demonstrated that the solvent induces predissocn. of the B3P0 +u of I2 state within 300 fs in CCl4, and within 40 fs in liq. Xe. 62 Refs. [on SciFinder (R)]