Infrared-induced rotational isomerization of 1,2-ethanediamine in argon matrices and conformational analysis by DFT calculation

Infrared spectra of 1,2-ethanediamine and its two deuterated species, ND2CH 2CH2ND2 and NH2CD2CD2NH2, were measured by matrix-isolation FTIR spectrosco py. Isomerization around the central C-C axis from two gauche conformers to one trans conformer was found to occur upon infrared irradiation. With an aid of density functional theory, DFT, calculations, where the 6-31++G** ba sis set was used to optimize geometrical structures, the gauche conformers were assigned to G(+)G(+)G(-) and TG(+)G(-) and the trans conformer to TTT. Wavelength dependence of the isomerization rates was examined using a tuna ble narrow band pass filter. It was found that relative quantum yields depe nd on excitation energy but not on the type of vibrational modes which abso rb infrared rays. (C) 1999 Elsevier Science B,V. All rights reserved.