VIBRATIONAL MAGNETIC DIPOLE-MOMENT OF ACETYLENE IN THE NU-5 MODE

The sign and approximate magnitude of the gyromagnetic ratio for the n u(5) doubly degenerate bending mode of acetylene are determined by use of rotationally resolved magnetic dichroism measurement of transition s to the singly excited vibrational state. By analysis of the J-depend ence of the apparent g-value for this transition, the vibrational g-fa ctor was determined from the experimental spectrum by moment analysis to be g(nu) = 0.48(25). This is the first such determination of g(nu) in a degenerate state of a linear molecule using MVCD and the first de termination of g(nu) for the nu(5) mode in acetylene. Simulated MVCD s pectra based on the accepted ground state rotational g-value and this determination of g(nu) agree with the observed intensity pattern, conf irming the analysis.