Nuclear and electronic dynamics in a wavepacket comprising bound Rydberg and valence electronic states of nitrogen from 12 to 15 eV are investigated using attosecond transient absorption. Vibrational quantum beats with a fundamental period of 50 femtoseconds persist for a picosecond in the b' (1)Sigma(+)(u) valence state. Multi- state calculations show that these coherences result primarily from near infraredinduced coupling between the inner and outer regions of the b' (1)Sigma(+)(u) state potential and the dark a'' (1)Sigma(+)(u) state. The excellent spectral and temporal resolution of this technique allows measurement of the anharmonicity of the b' (1)Sigma(+)(u) potential directly from the observed quantum beats. (C) 2017 Elsevier B.V. All rights reserved.