1. Theoretical Study of the Formic Acid-Water Complex in the First Excited State Jose M. Hermida-Ramón, Carlos M. Estévez. Departamento de Química Física. Facultade de Química. Universidade de Vigo. Spain

3. Ground state FAT-1 S 0

4. FAT-2 S 0

5. FAT-3 S 0

6. Binding energies (S 0 ) (kJ mol -1 ) 17.0 22.0 43.2 B3LYP/ 6-311++G(2d,2p)(1) CASPT2//CAS(8,8)/ 6-311++G(2d,2p) 22.9 FAT-3 29.6 FAT-2 47.6 FAT-1

7. Vertical p * <- n excitation Positive electronic density difference between the first singlet excited state and the ground state Negative electronic density difference between the first singlet excited state and the ground state

8. Vertical excitation energies Calculated at the CASPT2//CAS(8,8)/6-311++G(2d,2p) level 5.67 eV FAT-3 5.81 eV FAT-2 5.76 eV FAT-1 5.78 eV (5.83 eV exptl)(2) HCOOH

9. Excited state optimized geometries Distances (angstrom) C=O = 1.402 C-O = 1.347 O-H = 0.941 C-H = 1.076 Angles (degree) O-C=O = 112.2 H-C=O = 112.1 H-O-C= 110.6 Dihedrals (degree) O=C-H-O = 129.0 H-O-C=O = 68.5

10. First singlet excited state Distances (angstrom) C=O = 1.407 C-O = 1.340 O-H = 0.947 C-H = 1.077 Angles (degree) O-C=O = 112.3 H-C=O = 111.6 H-O-C= 110.2 Dihedrals (degree) O=C-H-O = 129.0 H-O-C=O = 64.5 FAT-1 S 1

11. Distances (angstrom) C=O = 1.406 C-O = 1.348 O-H = 0.941 C-H = 1.075 Angles (degree) O-C=O = 112.0 H-C=O = 111.6 H-O-C= 110.6 Dihedrals (degree) O=C-H-O = 128.7 H-O-C=O = 69.8 FAT-2 S 1

12. Distances (angstrom) C=O = 1.400 C-O = 1.353 O-H = 0.942 C-H = 1.076 Angles (degree) O-C=O = 111.8 H-C=O = 112.6 H-O-C= 110.7 Dihedrals (degree) O=C-H-O = 128.8 H-O-C=O = 72.5 FAT-3 S 1

13. 0-0 Band Origin CASPT2//CAS(8,8)/6-311+G(2d,2p) 4.54 eV (4.64 eV exptl)(2) HCOOH 4.62 eV FAT-3 4.73 eV FAT-2 4.70 eV FAT-1

14. Binding energies (S 1 ) (kJ mol -1 ) CASPT2//CAS(8,8)/6-311++G(2d,2p) 15.2 FAT-3 10.5 FAT-2 31.9 FAT-1