Coupled nuclear-electronic decay dynamics of O2 inner valence excited states revealed by attosecond XUV wave-mixing spectroscopy

Yen-Cheng Lin; Ashley P Fidler; Arvinder Sandhu; Robert R Lucchese; C William McCurdy; Stephen R Leone; Daniel M Neumark

doi:10.1039/d0fd00113a

Coupled nuclear-electronic decay dynamics of O₂ inner valence excited states revealed by attosecond XUV wave-mixing spectroscopy

Faraday Discuss. 2021 May 27;228(0):537-554. doi: 10.1039/d0fd00113a.

Authors

Yen-Cheng Lin¹, Ashley P Fidler¹, Arvinder Sandhu², Robert R Lucchese³, C William McCurdy⁴, Stephen R Leone⁵, Daniel M Neumark¹

Affiliations

¹ Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. dneumark@berkeley.edu and Department of Chemistry, University of California, Berkeley, California 94720, USA.
² Department of Physics, University of Arizona, Tucson, Arizona 85721, USA.
³ Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. dneumark@berkeley.edu.
⁴ Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. dneumark@berkeley.edu and Department of Chemistry, University of California, Davis, California 95616, USA.
⁵ Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. dneumark@berkeley.edu and Department of Chemistry, University of California, Berkeley, California 94720, USA and Department of Physics, University of California, Berkeley, CA 94720, USA.

PMID: 33595034
DOI: 10.1039/d0fd00113a

Abstract

Multiple Rydberg series converging to the O2+c4Σ-u state, accessed by 20-25 eV extreme ultraviolet (XUV) light, serve as important model systems for the competition between nuclear dissociation and electronic autoionization. The dynamics of the lowest member of these series, the 3sσg state around 21 eV, has been challenging to study owing to its ultra-short lifetime (<10 fs). Here, we apply transient wave-mixing spectroscopy with an attosecond XUV pulse to investigate the decay dynamics of this electronic state. Lifetimes of 5.8 ± 0.5 fs and 4.5 ± 0.7 fs at 95% confidence intervals are obtained for v = 0 and v = 1 vibrational levels of the 3s Rydberg state, respectively. A theoretical treatment of predissociation and electronic autoionization finds that these lifetimes are dominated by electronic autoionization. The strong dependence of the electronic autoionization rate on the internuclear distance because of two ionic decay channels that cross the 3s Rydberg state results in the different lifetimes of the two vibrational levels. The calculated lifetimes are highly sensitive to the location of the 3s potential with respect to the decay channels; by slight adjustment of the location, values of 6.2 and 5.0 fs are obtained computationally for the v = 0 and v = 1 levels, respectively, in good agreement with experiment. Overall, an intriguing picture of the coupled nuclear-electronic dynamics is revealed by attosecond XUV wave-mixing spectroscopy, indicating that the decay dynamics are not a simple competition between isolated autoionization and predissociation processes.