Watching a single molecule move on its intrinsic timescale has been one of the central goals of modern nanoscience, and calls for measurements that combine ultrafast temporal resolution1,2,3,4,5,6,7,8 with atomic spatial resolution9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30. Steady-state experiments access the requisite spatial scales, as illustrated by direct imaging of individual molecular orbitals using scanning tunnelling microscopy9,10,11 or the acquisition of tip-enhanced Raman and luminescence spectra with sub-molecular resolution26,27,28. But tracking the intrinsic dynamics of a single molecule directly in the time domain faces the challenge that interactions with the molecule must be confined to a femtosecond time window. For individual nanoparticles, such ultrafast temporal confinement has been demonstrated18 by combining scanning tunnelling microscopy with so-called lightwave electronics1,2,3,4,5,6,7,8, which uses the oscillating carrier wave of tailored light pulses to directly manipulate electronic motion on timescales faster even than a single cycle of light. Here we build on ultrafast terahertz scanning tunnelling microscopy to access a state-selective tunnelling regime, where the peak of a terahertz electric-field waveform transiently opens an otherwise forbidden tunnelling channel through a single molecular state. It thereby removes a single electron from an individual pentacene molecule’s highest occupied molecular orbital within a time window shorter than one oscillation cycle of the terahertz wave. We exploit this effect to record approximately 100-femtosecond snapshot images of the orbital structure with sub-ångström spatial resolution, and to reveal, through pump/probe measurements, coherent molecular vibrations at terahertz frequencies directly in the time domain. We anticipate that the combination of lightwave electronics1,2,3,4,5,6,7,8 and the atomic resolution of our approach will open the door to visualizing ultrafast photochemistry and the operation of molecular electronics on the single-orbital scale.
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We thank A. Pöllmann, F. Albrecht, R. Kronfeldner, M. Eisele and M. Furthmeier for assistance, and F. Evers, F. A. Hegmann, V. Jelic, P. C. M. Planken, M. Grifoni and K. Richter for discussions. We acknowledge financial support from the Volkswagen Foundation (Lichtenberg program), the European Research Council through grant number 305003 (QUANTUMsubCYCLE), and the Deutsche Forschungsgemeinschaft (DFG) through GRK 1570 and research grants HU1598/3 and CO1492/1. T.L.C. thanks the A. v. Humboldt Foundation.