NMR and Double Resonance Spectra of CH2F2 and CH3CHF2 in the Gas Phase

Abstract

The methyl proton spectrum of CH₃CHF₂ in the gas phase consists of three broad peaks, with a sharp doublet superimposed on the central broad peak. The proton spectrum of CH₂F₂ also consists of three broad features, with a single sharp peak superimposed on the central broad peak. Proton—fluorine double resonance measurements show that the width of the broad features in the proton spectra is determined by fluorine relaxation processes, and that the broad peaks arise from transitions between states with K(F)=1, while the sharp lines must be assigned to transitions between states with K(F)=0. The relative widths of the broad peaks are consistent with the assumption that the collision‐modulated spin—rotation interaction provides the dominant fluorine relaxation mechanism, but that this interaction is not important for proton relaxation. The addition of oxygen to CH₃CHF₂ causes the broadening of the sharp central doublet in the methyl proton spectrum. However, it is shown by double resonance that the dominant effect of the addition of oxygen to CH₃CHF₂ is to decrease the proton relaxation time, rather than to increase the fluorine singlet—triplet conversion rate.