Decelerated molecular beams for high-resolution spectroscopy

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Ultimately, the resolution of any spectroscopic experiment is limited by the interaction time between the particles that are to be examined and the measuring device. The obtainable spectroscopic resolution in a molecular beam experiment can be considerably improved using samples of slow molecules, as produced, for example, in a Stark-decelerator. This is demonstrated here by measuring the inversion tunneling spectrum of ${}^{15}{\rm ND}_3$ using a pulsed molecular beam that has been decelerated to about 52 m/s. Hyperfine resolved inversion transitions in ${}^{15}{\rm ND}_3$ in the $\left\vert J,K\right > = \left\vert 1,1\right > $ state (around 1.43 GHz) are induced in a microwave region, and ${}^{15}{\rm ND}_3$ molecules that have undergone the transition are subsequently detected using a UV-laser based ionization detection scheme. To increase the signal intensity, the decelerated molecular beam is both transversally and longitudinally focused into the laser detection region. The observed spectral width of individual hyperfine transitions in the fully resolved spectrum is about 1 kHz, and the standard deviation of the best fit is 62 Hz.

Received: 7 September 2004, Published online: 23 November 2004


33.15.Pw Fine and hyperfine structure - 33.20.Bx Radio-frequency and microwave spectra - 33.40. + f Multiple resonances - 33.70.Jg Line and band widths, shapes, and shifts - 39.10. + j Atomic and molecular beam sources and techniques