The first infrared predissociation spectra of the pyrene and doubly-dehydrogenated pyrene cations (C16H10˙+; Py+ and C16H8˙+; ddPy+) are presented. The vibrationally resolved spectrum of ddPy+ is dominated by absorption features from two isomers.
1,4-Naphthoquinone (1,4-NQ) is an important product of naphthalene oxidation, and it appears as a motif in many biologically active compounds. We have investigated the structure of 1,4-NQ using chirped-pulse Fourier transform microwave spectroscopy and quantum chemistry calculations. The rotational spectra of the parent species, and its 13 C and 18 O isotopologues were observed in natural abundance, and their spectroscopic parameters were obtained. This allowed the determination of the substitution r s , mass-weighted r m and semi-experimental r e SE structures of 1,4-NQ. The obtained structural parameters show that the quinone moiety mainly changes the structure of the benzene ring where it is inserted, modifying the CÀ C bonds to having predominantly single or double bond character. Furthermore, the molecular electrostatic surface potential reveals that the quinone ring becomes electron deficient while the benzene ring remains a nucleophile. The most electrophilic areas are the hydrogens attached to the double bond in the quinone ring. Knowledge of the nucleophilic and electrophilic areas in 1,4-NQ will help understanding its behaviour interacting with other molecules and guide modifications to tune its properties.
Many citizen science projects depend on colour vision. Examples include classification of soil or water types and biological monitoring. However, up to 1 in 11 participants are colour blind. We simulate the impact of various forms of colour blindness on measurements with the Forel-Ule scale, which is used to measure water colour by eye with a 21-colour scale. Colour blindness decreases the median discriminability between Forel-Ule colours by up to 33% and makes several colour pairs essentially indistinguishable. This reduces the precision and accuracy of citizen science data and the motivation of participants. These issues can be addressed by including uncertainty estimates in data entry forms and discussing colour blindness in training materials. These conclusions and recommendations apply to colour-based citizen science in general, including other classification and monitoring activities. Being inclusive of the colour blind increases both the social and scientific impact of citizen science.
Non-covalent interactions between aromatic molecules
and water
are fundamental in many chemical and biological processes, and their
accurate description is essential to understand molecular relative
configurations. Here we present the rotational spectroscopy study
of the water complexes of the polycyclic aromatic hydrocarbon 1,4-naphthoquinone
(1,4-NQ). In 1,4-NQ-(H2O)1,2, water molecules
bind through O–H···O and C–H···O
hydrogen bonds and are located on the plane of 1,4-NQ. For 1,4-NQ-(H2O)3, in-plane and above-plane water configurations
are observed exhibiting O–H···O, C–H···O,
and lone pair···π-hole interactions. The observation
of different water arrangements for 1,4-NQ-(H2O)3 allows benchmarking theoretical methods and shows that they have
great difficulty in predicting energy orderings due to the strong
competition of C–H···O binding with π
and π-hole interactions. This study provides important insight
into water interactions with aromatic systems and the challenges in
their modeling.
Gas-phase
IR–UV double-resonance laser spectroscopy is an
IR absorption technique that bridges the gap between experimental
IR spectroscopy and theory. The IR experiments are used to directly
evaluate predicted frequencies and potential energy surfaces as well
as to probe the structure of isolated molecules. However, a detailed
understanding of the underlying mechanisms is, especially in the far-IR
regime, still far from complete, even though this is crucial for properly
interpreting the recorded IR absorption spectra. Here, events occurring
upon excitation to vibrational levels of polycyclic aromatic hydrocarbons
by far-IR radiation from the FELIX free electron laser are followed
using resonance-enhanced multiphoton ionization spectroscopy. These
studies provide detailed insight into how ladder climbing and anharmonicity
influence IR–UV spectroscopy and therefore the resulting IR
signatures in the far-IR region. Moreover, the potential energy surfaces
of these low-frequency delocalized modes are investigated and shown
to have a strong harmonic character.
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