GAS PHASE MAGNETIC VIBRATIONAL CIRCULAR DICHROISM. A POSSIBLE WAY TO DETERMINE THE ROTATIONAL g-FACTOR OF THE MOLECULAR ZEEMAN EFFECT

Author Institution: Department of Chemistry, University of Illinois at ChicagoWe have focused on gas phase, rotationally resolved magnetic vibrational circular dichrosim (MVCD) recently. The MVCD measurements of some small molecules were made at $0.5 cm^{-1}$ resolution using an FTIR spectrometer with a superconductive magnet operated at 8T. These show that the MVCD A-terms caused by the first order molecular Zeeman effect provide information with regard to the sign and magnitude of the rotational g-factor for the excited vibrational state being observed in the infrared transition. The negative A-terms of some $T_{d}$ group molecules. $CH_{4}$ and $CD_{4}$, and of some $C_{3v}$ group molecules, $NH_{3}$ and $ND_{3}$, give evidence of a positive $g_{J}$. By use of moment analysis we can calculate ${A_{1}}/{D_{0}}$ which can be related to $g_{J}$ by ${A_{1}}/{D_{0}} = 2(\mu_{N}/\mu_{B})g_{J}$. The $g_{J}$ values we obtained for $\nu_{4}$ of $CH_{4}$ and for $\nu_{2}$ of $NH_{3}$ are +0.44 and +0.9 respectively. The difference from the ground vibrational state $g_{J}$ values, which were measured by molecular beam magnetic resonance technique may be due to the limitations of our low resolution instrument or to the vibrational contribution