MAGNETO-INFRARED SPECTRA OF MATRIX-ISOLATED NIH AND NIH2 MOLECULES AND THEORETICAL CALCULATIONS OF THE LOWEST ELECTRONIC STATES OF NIH2

Two vibronic transitions, (2) Delta(3/2)(upsilon'=0)<--(2) Delta(5/2)( upsilon ''=0) and 2 Pi(3/2)(upsilon'=0)<--(2) Delta(5/2)(upsilon ''=0) at 923 and 2560 cm(-1), respectively, were observed for NiH in solid argon (and krypton) at 4 K. These Omega=3/2<--Omega=5/2 transitions we re shifted and broadened by magnetic fields of up to 4 T. Also, its gr ound state vibrational frequency has been observed in neon, argon, and krypton matrices. Bands in the 600-2000 cm(-1) region were assigned a s frequencies of the NiH2 (NiD2, NiHD) molecule. Contrary to earlier a b initio calculations, this assignment implies that the molecule is st rongly bent in its ground electronic state. This discrepancy was explo red theoretically by considering the lowest triplet (linear) and singl et (bent) states of NiH2. The relative energies of the two states have not been satisfactorily resolved, but the calculated structural and v ibrational properties of the singlet state are in good agreement with the observations. (C) 1997 American Institute of Physics.