[Analysis of differential metabolites of spikes of Prunella vulgaris at different stages based on UPLC-MS/MS].

Prunella vulgaris, aptly named for its withering at the summer solstice, displays significant variation in quality arising from differing harvest time. However, research on the chemical composition changes of its spikes at various stages is limited, and the specific metabolites remain unclear. In order to elucidate the metabolites and metabolic pathways of the spikes of P. vulgaris, the current study deployed ultra-performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS) and targeted metabolomics to characterize the compound variability in the spikes of P. vulgaris across different periods. Multivariate statistical techniques such as principal component analysis(PCA) and orthogonal partial least squares-discriminant analysis(OPLS-DA) were used to identify the differences in metabolites, and relevant metabolic pathways were analyzed. A total of 602 metabolites were identified by metabolomics, of which organic acids and their derivatives were the most abundant, followed by flavonoids. Multiple differential metabolites, including p-hydroxybenzoic acids and gallic acids were identified based on variable importance in projection(VIP)>1 and P<0.05. The results of enrichment analysis suggested that isoflavonoids biosynthesis, aminobenzoate degradation, benzoate degradation, anthocyanins biosynthesis, metabolic pathways, microbial metabolism in different environments, secondary plant metabolite biosynthesis, tryptophan metabolism, and phenylpropanoid synthesis were the main metabolic pathways. These results intend to elucidate the dynamic changes of differential metabolites of P. vulgaris and provide a theoretical basis for further study of the harvesting mechanism of spikes of P. vulgaris.

Collision-Energy Dependent Stereodynamics of Dissociative Charge Exchange Reaction between Ar+ and CO.

Long-distance charge-dipole attraction between atomic ion and randomly oriented polar molecule potentially makes the molecular orientation, which profoundly influences the products' kinetics of collisional reaction. Using the three-dimensional ion velocity map imaging technique, here we report a collision-energy dependent stereodynamics of dissociative charge exchange reaction Ar+ + CO → Ar + O + C+ in a range of 7.46-9.97 eV. At the lowest collision energy, the most C+ products are forward-scattered and are along the collision axis and are attributed to three different dissociation channels including the predominant one experiencing the rotating intermediate ArC+. At the high collision energies, the remarkably diffusive distribution of C+ arises from the prompt dissociation of the rebounded CO+. The different dynamic processes arising from the nearly collinear collision are elaborated explicitly on the basis of the data analyses using the Doppler kinetics models.

Superposition-state N2 + produced in the intermolecular charge transfer from low-energy Ar+ to N2.

Molecular electronic or vibrational states can be superimposed temporarily in an extremely short laser pulse, and the superposition-state transients formed therein receive much attention, owing to the extensive interest in molecular fundamentals and the potential applications in quantum information processing. Using the crossed-beam ion velocity map imaging technique, we disentangle two distinctly different pathways leading to the forward-scattered N2 + yields in the large impact-parameter charge transfer from low-energy Ar+ to N2. Besides the ground-state (X2Σg +) N2 + produced in the energy-resonant charge transfer, a few slower N2 + ions are proposed to be in the superpositions of the X2Σg +-A2Πu and A2Πu-B2Σu + states on the basis of the accidental degeneracy or energetic closeness of the vibrational states around the X2Σg +-A2Πu and A2Πu-B2Σu + crossings in the non-Franck-Condon region. This finding potentially shows a brand-new way to prepare the superposition-state molecular ion.

Ion-Molecule Charge Exchange Reactions between Ar+ and trans-/cis-Dichloroethylene.

We report an ion velocity imaging study of the charge exchange reactions between Ar+ ion and trans-/cis-dichloroethylene in the collision energy range of 2.1-9.5 eV, and we find that the energy-resonant charge transfer plays a dominant role in the large impact-parameter reaction. The parent yields C2H2Cl2+ in the high-lying excited states are directly produced in the charge exchange reactions, while they prefer spontaneous fragmentations in photoionization. This significant difference indicates that the present charge exchange reactions are much slower than the photoelectron detachment. The structural relaxations of the target molecule are allowed in multiple dimensions of freedom during the charge transfer, which should be frequently observed for the charge exchange reactions with large molecules.

Stereodynamics Observed in the Reactive Collisions of Low-Energy Ar+ with Randomly Oriented O2.

Stereodynamics of the collisional reaction between mutually aligned or oriented reactants has been a striking topic of chemical dynamics for decades. However, the stereodynamic aspects are scarcely revealed for the low-energy collision with a randomly oriented target. Here in the dissociative charge-exchange reaction between randomly oriented O2 and low-energy Ar+, we, using the three-dimensional ion velocity map imaging technique, clearly observe a linear alignment and a nearly isotropic distribution of the O+ yields along the collision axis. These observations are rationalized with the Doppler kinetic models in which the O2 bond is assumed to be parallel or unparallel to the collision axis of the large impact parameter collision. The linearly aligned O+, as the predominant yield, is produced in the parallel collision, while a rotating O2+, as the intermediate in the unparallel collision, leads to the isotropic distribution of O+.

Direct observation of long-lived cyanide anions in superexcited states.

The cyanide anion (CN-) has been identified in cometary coma, interstellar medium, planetary atmosphere and circumstellar envelopes, but its origin and abundance are still disputed. An isolated CN- is stabilized in the vibrational states up to ν = 17 of the electronic ground-state 1Σ+, but it is not thought to survive in the electronic or vibrational states above the electron autodetachment threshold, namely, in superexcited states. Here we report the direct observation of long-lived CN- yields of the dissociative electron attachment to cyanogen bromide (BrCN), and confirm that some of the CN- yields are distributed in the superexcited vibrational states ν ≥ 18 (1Σ+) or the superexcited electronic states 3Σ+ and 3Π. The triplet state can be accessed directly in the impulsive dissociation of BrCN- or by an intersystem transition from the superexcited vibrational states of CN-. The exceptional stability of CN- in the superexcited states profoundly influences its abundance and is potentially related to the production of other compounds in interstellar space.

Probing the Potential Energy Surfaces of BrCN- by Dissociative Electron Attachment.

State coupling certainly determines the topologic features of the molecular potential energy surface (PES) and potentially diversifies chemical reaction pathways. Here we report the new PESs of BrCN- in the low-lying electronic states that are distinctly different from the previous predictions in the short Br-CN bond region but validated by the high-resolution ion velocity imaging measurements of low-energy dissociative electron attachment (DEA) to BrCN. Besides the vibrating CN- ions produced in the fast Br-CN bond stretching motions, we confirm that the ro-vibrating CN- ions with a nearly isotropic angular distribution are produced by receiving a torque in the combinational motion of Br-CN bond bending and stretching. The latter process is closely related to the potential well of BrCN- at the first excited state A2Π3/2 that arises from the Π-Σ state couplings. Our findings not only suggest that the PESs of other anionic cyanogen halides are in dire need of reexamination but also show that ion velocity imaging of the DEA process is a powerful experimental method for evaluating the theoretical PESs of molecular anions.

Vibrationally resolved photoemissions of N2 (C3Πu → B3Πg) and CO (b3Σ+ → a3Π) by low-energy electron impacts.

Vibrationally resolved photoemission spectra of the electronic-state transitions C3Πu → B3Πg of N2 and b3Σ+ → a3Π of CO following low-energy electron impacts are measured with a crossed-beam experimental arrangement. The absolute cross sections of C3Πu (ν') → B3Πg (ν″) of N2 are presented for the vibrational state-to-state transitions (ν',ν″) = (0,0), (0,1), (1,0), (1,2), and (2,1). The excitation cross sections of the metastable state C3Πu of N2 show the maxima at the electron-impact energies 14.10 (ν' = 0) eV and 14.50 (ν' = 1) eV, which are potentially related to the core-excited vibrational Feshbach resonant state 2Σu + of N2 - formed by electron attachment. The absolute cross sections of b3Σ+ (ν' = 0) → a3Π (ν″ = 0, 1, 2, 3, 4) of CO are given by the calibrations with those of N2 measured in this work. Besides the maximum excitation cross section 5.85 × 10-18 cm2 at 10.74 eV of the CO b3Σ+ (ν' = 0) state, some fine structures on the excitation function profile are attributed to different shapes and Feshbach resonant states of CO- formed by electron attachment, while the others arise from the direct electron-impact excitation. Some discrepancies, particularly for N2, between the present data and the results available in the literature studies arise from different experimental techniques and data-processing procedures. Furthermore, contributions of physical processes such as wave-packet evolution and non-Franck-Condon dynamics are highlighted here.

Synchronous and asynchronous dynamics of the concerted three-body dissociations of temporary negative ion CH2F2.

Molecular concerted three-body dissociation is a fast process, but still can be classified into synchronous and asynchronous pathways. It is challenging in experiments to evaluate different contributions of the aforementioned mechanisms. Here, we report an experimental identification of the synchronous and asynchronous concerted three-body dissociations of temporary negative ion CH2F2 - at an electron-molecule resonant state formed by electron attachment. The synchronous-asynchronous branching ratios indicate that the asynchronous process is predominant although the synchronous contribution is slightly enhanced with the increase in the electron attachment energy. This study provides two intuitive pictures of the concerted three-body dissociations, in particular for the nonequivalent-bond cleavages of a polyatomic molecule.