Abstract
This paper reports an advanced study of the excited ionic states of the gas-phase nitrogen molecule in the binding-energy region of 22–34 eV, combining ultrahigh-resolution resonant photoemission (RPE) and ab initio configuration-interaction calculations. The RPE spectra are recorded for nine photon energies within the N absorption resonance of by using a photon bandwidth that is considerably smaller than lifetime broadening, and the dependence on excitation energy of the decay spectra is analyzed and used for the first assignment of 12 highly overlapped molecular states. The effect on the RPE profile of avoided curve crossings between the final ionic states is discussed, based on theoretical simulations that account for vibronic coupling, and compared with the experimental data. By use of synchrotron radiation with high spectral brightness, it is possible to selectively promote the molecule to highly excited vibrational sublevels of a core-excited electronic state, thereby controlling the spatial distribution of the vibrational wave packets, and to accurately image the ionic molecular potentials. In addition, the mapping of the vibrational wave functions of the core-excited states using the bound final states with far-from-equilibrium bond lengths has been achieved experimentally for the first time. Theoretical analysis has revealed the rich femtosecond nuclear dynamics underlying the mapping phenomenon.
5 More- Received 23 November 2012
- Publisher error corrected 9 April 2013
DOI:https://doi.org/10.1103/PhysRevX.3.011017
This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Corrections
9 April 2013
Erratum
Publisher’s Note: Single-Molecule X-Ray Interferometry: Controlling Coupled Electron-Nuclear Quantum Dynamics and Imaging Molecular Potentials by Ultrahigh-Resolution Resonant Photoemission and Ab Initio Calculations [Phys. Rev. X 3, 011017 (2013)]
V. Kimberg, A. Lindblad, J. Söderström, O. Travnikova, C. Nicolas, Y. P. Sun, F. Gel’mukhanov, N. Kosugi, and C. Miron
Phys. Rev. X 3, 029901 (2013)
Popular Summary
Absorption of an x-ray photon of proper wavelength by a molecule can take the molecule to a highly excited electronic state accompanied by molecular vibration. Molecules in these states are very reactive chemically. Such highly excited and reactive molecules are ubiquitous and important in diverse fields such as plasma physics, astrochemistry, radiation physics, and photochemistry. But, how much do we actually understand the quantum dynamics of these unstable species? The answer is: not yet much, even in the case of one of the simplest molecules, the nitrogen molecule. In this work, we apply state-of-the-art resonant photoemission spectroscopy to the study of the electron and nuclear dynamics of highly excited nitrogen molecules and map out, with an unprecedented resolution and degree of comprehensiveness, the vibrational wave functions and their ultrafast evolution with time.
A highly electronically excited nitrogen molecule is very unstable and lives over an extremely short time scale of a few femtoseconds. Its decay yields a molecular ion through the so-called Auger process, where a high-energy electron is ejected when another electron falls into the hole left by the initial excited electron. The Auger-electron emission spectra naturally contain fundamental information about the extremely short-lived intermediate states, and not least, also on what the vibrational motion of the resulting molecular ion is like—knowledge that has not been available so far. It is such spectra that we measure experimentally and analyze.
Indeed, taking advantage of the high spectral brightness of the synchrotron radiation at the PLEIADES beam line at the SOLEIL Synchrotron, Paris-Saclay campus, we are able to selectively excite nitrogen molecules, control the spatial forms of the vibrational wave functions of the excited molecules, and follow the time evolution of the vibrational wave functions of the final molecular ions. Adding to our toolbox first-principles calculations of the evolution of the vibrational wave functions, that correctly account for the coupling between the nuclear and electronic motion in highly excited, and thus deformed, molecules, we have succeeded in not only mapping out for the first time the actual shapes of the vibrational wave functions of highly excited nitrogen molecules, but also identifying a few ionic states that have not been known before.
This approach is not only limited to the nitrogen molecule: It can be extended to studies of excited ionic states of even larger molecules, and can also be easily transposed to neutral molecular states by detecting the radiative decay instead of the electron emission by Auger decay.