THE NU(1)-MODE OF C3 IN AR AND KR MATRICES - EVIDENCE FOR A BENT STRUCTURE(NU(3) COMBINATION)

The nu1 + nu3 combination mode of laser-ablated C3 has been observed i n Ar and Kr matrices for all six possible C-12/C-13 isotopomers. The n u1 totally symmetric mode frequencies have been determined by differen ce with the known nu3 asymmetric stretching frequencies, corrected for anharmonicity effects. A comparison of certain isotopomer pairs revea ls that C3 is bent in these matrices. A normal coordinate analysis usi ng four force constants resulted in an excellent fit of the 12 observe d frequencies (nu1 and nu3 for six isotopomers). From the fit, a value for the nu2 bending mode frequency of 82 cm-1 was obtained. This is s hown to be in good agreement with the value obtained from the C3 phosp horescence spectrum. Finally, the molecular bending angle which was de termined to be 160.0-degrees (in Ar and Kr) is shown to match very wel l with the predicted value from ab initio theory (161.6-degrees) and f rom a fitting of a Morse oscillator-rigid bender potential to gas phas e vibrational frequencies (162.5-degrees). The influence of the matrix environment on the vibrational force constants and frequencies of C3 is discussed.