Time-resolved infrared-microwave double resonance in 13CH3F: Theory and experiment

Abstract

Infrared‐microwave double resonance experiments on ¹³CH₃F are described which lead to a direct measurement of T₁, the relaxation time due to population differences for the two transitions J = 3 → J = 4; K = 3 and J = 4 → J = 5; K = 3 in the ground vibrational state. We find T₁ = (10.5 ± 0.6) μsec mtorr. Comparing this work with low‐power linewidth measurements which measure T₂, the relaxation time of the induced polarization, indicates that T₁ = T₂ for the above two transitions. The theory used to interpret the experiments is developed starting from the density matrix formalism which leads to the electric dipole analog of the Bloch equations in nuclear magnetic resonance. The equations are solved for the conditions appropriate to this experiment which gives the results involving T₁ and T₂. The theory developed here should be of use in interpreting time‐resolved infrared‐microwave experiments in the future.