Magnetic deflection spectrum of VCl₄

The magnetic deflection spectra of VCl₄ seeded into supersonic beams of the rare gases have been determined. It is found that in the heavier rare gases (Ar, Kr, and Xe) the Stern-Gerlach splitting patterns are just those expected for a molecule in a spin-doublet state, as complicated by the presence of nondeflecting (VC1₄)_X clusters. In these beams, the satellite splittings of unclustered VC1₄ scale with the square of the beam velocities, and there is no evidence in the Stern-Gerlach spectra for the rapid (10⁻⁹ s) intramolecular spin relaxation (ISR) so apparent in the EPR and NMR spectra of this molecule in condensed phases. Modeling of the ISR effect on SG deflection spectra and comparison of these results with experiment shows that if ISR is in any way active in beam-cooled VC1₄, the spin relaxation time is longer than 10⁻⁴ s. By contrast, the deflection spectrum of VC1₄ seeded into He is far more compressed than otherwise expected, suggesting that ISR may be at work in this case. Analysis of the observed Stern-Gerlach band shape of VC1₄ in the He beam shows that if ISR is the cause of the anomalous spectrum, then the ISR time is approximately 10⁻⁶ s. The use of magnetic deflection to determine the possible association of the carrier gases with the paramagnetic target molecule is presented as an illustration of neutral-molecule mass spectrometry.