Abstract
Time-resolved dynamics of high-lying Rydberg states of ammonia (NH3) prepared by using a vacuum ultraviolet (VUV) pump (∼9.3 eV) and an ultraviolet (UV) probe (∼4.7 eV) pulse are reported using photoelectron imaging detection. After photoexcitation, two main features appear in the photoelectron spectrum with vertical binding energies of ∼1.8 eV and ∼3.2 eV and with distinctly different anisotropy parameters β of ∼1.3 and ∼0.7, respectively. This information allows the unambiguous assignment of the respective Rydberg states and disentangles the induced electronic and vibrational dynamics. The combination of velocity-map imaging with femtosecond VUV and UV pulses is shown to offer an attractive approach for studying the dynamics of high-lying Rydberg states of small molecules.
Highlights
The few studies that have involved high-lying Rydberg states have been confined to static measurements1,8,9 because of a lack of vacuum ultraviolet (VUV) femtosecond laser sources
While there are certainly differences between the photoinduced molecular dynamics of C–N bonds and N–H bonds,12 the study of small molecules can shed light on the fundamental dynamics of moieties that could be clouded by increased complexity, in addition to having the benefit of being accessible to state-of-the-art quantum-chemical calculations without facing extreme computational costs
Our time-resolved photoelectron imaging experiment of the hsoiguhrc-ley,inshgoRwysdabneruglstrtaatfeasstopf oNpHul3a,taioccnestrsaednsbfeyraftraobmle-tthoepEV′′UsVtatlieghtot the C ′ state due to internal conversion mediated by the umbrella motion
Summary
Many spectroscopic and theoretical studies have been devoted to ammonia (NH3). Studies which have focused on electronically excited NH3 have been mainly focused on the low-lying Rydberg states (∼6 eV) investigating their complex photodissociation dynamics. The few studies that have involved high-lying Rydberg states have been confined to static measurements because of a lack of vacuum ultraviolet (VUV) femtosecond laser sources.In many biologically relevant molecules, such as amino acids, the sp hybridized nitrogen is the central functional unit in defining their photochemistry, e.g., through valence-Rydberg mixing that causes their surprising stability to UV light. Further understanding of the mechanisms by which these nitrogen centers are able to efficiently redistribute absorbed UV light has a natural imperative that invites further study. Studies which have focused on electronically excited NH3 have been mainly focused on the low-lying Rydberg states (∼6 eV) investigating their complex photodissociation dynamics.. The few studies that have involved high-lying Rydberg states have been confined to static measurements because of a lack of vacuum ultraviolet (VUV) femtosecond laser sources. Further understanding of the mechanisms by which these nitrogen centers are able to efficiently redistribute absorbed UV light has a natural imperative that invites further study. While there are certainly differences between the photoinduced molecular dynamics of C–N bonds and N–H bonds, the study of small molecules can shed light on the fundamental dynamics of moieties that could be clouded by increased complexity, in addition to having the benefit of being accessible to state-of-the-art quantum-chemical calculations without facing extreme computational costs
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