Probing the Dynamics of Rydberg and Valence States of Molecular Nitrogen with Attosecond Transient Absorption Spectroscopy

Abstract

An attosecond pulse is used to create a wavepacket in molecular nitrogen composed of multiple bound and autoionizing electronic states of Rydberg and valence character between 12 and 16.7 eV. A time-delayed, few-femtosecond, near-infrared (NIR) laser pulse is used to couple individual states in the wavepacket to multiple neighboring states, resulting in time-dependent modification of the absorption spectrum and revealing both individual quantum beats of the wavepacket and the energy shifts of the excited states in the presence of the strong NIR field. The broad bandwidth of the attosecond pulse and high energy resolution of the extreme ultraviolet spectrometer allow the simultaneous observation of time-dependent dynamics for many individual vibrational levels in each electronic state. Quantum beating with periods from 1.3 to 12 fs and transient line shape changes are observed among vibrational levels of a progression of electronically autoionizing Rydberg states leading to the excited A (2)Πu N2(+) ion core. Vibrational levels in the valence b (1)Πu state exhibit 50 fs oscillation periods, revealing superpositions between individual vibrational levels within this state. Comparisons are made to previous studies of electronic wavepackets in atoms that highlight similarities to atomic behavior yet illustrate unique contributions of the diatomic molecular structure to the wavepacket, including the influence of different electronic potentials and vibrational-level-specific electronic dynamics.

Reconstruction of an excited-state molecular wave packet with attosecond transient absorption spectroscopy

“…These features reveal information about the field-free evolution of the electronic wave packet in the interval between the two pulses [2,41,42]. In the case of molecules, dipole absorption reflects nuclear dynamics as well [18]. According to the adiabatic approximation [43], the electronic response to the nuclear motion is instantaneous.…”

“…With the availability of high-resolution VUV spectrometers [15], one can conceivably monitor the recurrence of the vibronic wave packet created close to a localized reaction center, even in solution. ATAS has already been applied successfully to selected studies of strongfield ionization [5] and dissociation [16], wave-packet motion [3,4,6,17,18], and correlated electron dynamics [19][20][21][22], as well as phase transition dynamics in condensed matter [23,24], with unprecedented energy and time resolution. As ATAS encodes both the amplitudes and phases of interacting states, reconstruction and control of an electron wave packet-in both space and time-has been achieved [22].…”

Probing autoionizing states of molecular oxygen with XUV transient absorption: Electronic-symmetry-dependent line shapes and laser-induced modifications

“…2(b). To highlight the NIR induced absorbance change relative to continuum absorption, Fourier high pass filter is used to remove slow variation of underlying spectral profile, as also used in [27,36]. The vertical axis of the spectrogram refers to milli-optical density change (mOD).…”

“…Molecular ATAS is a largely unexplored topic and very few studies have been conducted so far [27,28]. Here we present a joint experimental-theoretical study of the autoionizing Rydberg states of O 2 .…”

XUV Transient Absorption Spectroscopy: Probing Laser-Perturbed Dipole Polarization in Single Atom, Macroscopic, and Molecular Regimes

“…However, there have been only a few experimental attempts to investigate laser modification of molecular polarization, except for some initial studies in diatomic systems such as H 2 , N 2 , and O 2 [31][32][33], and to the best of our knowledge, no work has been conducted in polyatomic molecules. Here, we demonstrate an application of ATAS to investigate the polyatomic SF 6 molecule that exhibits octahedral geometry.…”