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In this study, the conformational preferences and photochemistry of acrylic acid (AA, CH2=CHCOOH) monomer isolated in cryogenic argon and krypton matrices were interpreted, based on results of quantum chemical calculations. Natural bond orbital analysis allowed to shed light on the main electronic effects determining the relative stability of the conformers of the molecule in the ground electronic state. The conformational isomerization taking place upon UV-irradiation of the matrix-isolated compound (λ ∼ 243 nm) was explained, based on theoretical complete active space self-consistent field/complete active space with second order perturbation theory (CASSCF/CASPT2) and time-dependent density functional theory (TD-DFT) results, allowing to rationalize the nearly equal populations of the two lowest energy conformers of the molecule observed in the photostationary state. Besides, details of the infrared spectra of the compound were reinterpreted based on the calculated spectra for the two most stable conformers of the molecule. In particular, the assignments for the out-of-plane A″ symmetry vibrations were revised. [ABSTRACT FROM AUTHOR]

Ab initio calculations reveal that radiative lifetime of the lowest excited singlet state of 2-aminopyridine molecule should be around 20 ns, consistent with the molecules of the same type but is about one order of magnitude larger than the claimed experimental fluorescent lifetime in recent years. An S1/S0 conical intersection close to the S1 state has been located, which could be the possible nonradiative channel that is responsible for the fast decay observed in the experiment. [ABSTRACT FROM AUTHOR]