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A Ce atom reaction with propene is carried out in a pulsed laser vaporization molecule beam source. Several Ce–hydrocarbon species formed by the C—H and C—C bond activation of propene are observed by time-of-flight mass spectrometry, and Ce(C3Hn) (n = 4 and 6) are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and density functional theory, multiconfiguration, and relativistic quantum chemical calculations. The MATI spectrum of each species consists of two vibronic band systems, each with several vibronic bands. Ce(C3H6) is identified as an inserted species with Ce inserting into an allylic C—H bond of propene and Ce(C3H4) as a metallocycle through 1,2-vinylic dehydrogenation. Both species have a Cs structure with the Ce 4f16s1 ground valence electron configuration in the neutral molecule and the Ce 4f1 configuration in the singly charged ion. The two vibronic band systems observed for each species are attributed to the ionization of two pairs of the lowest spin–orbit coupled states with each pair being nearly degenerate. [ABSTRACT FROM AUTHOR]

Metal-mediated N–H and C–H bond activation of aliphatic amines is an effective strategy for synthesizing biologically important molecules. Ln (Ln = La and Ce) atom reactions with dimethylamine are carried out in a pulsed-laser vaporization supersonic molecular beam source. A series of dehydrogenation species are observed with time-of-flight mass spectrometry, and the dehydrogenated Ln-containing species in the formula Ln(CH2NCH3) are characterized by single-photon mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical calculations. The theoretical calculations include density functional theory for both Ln species and multiconfiguration self-consistent field and quasi-degenerate perturbation theory for the Ce species. The MATI spectrum of La(CH2NCH3) consists of a single vibronic band system, which is assigned to the ionization of the doublet ground state of N-methyl-lanthanaaziridine. The MATI spectrum of Ce(CH2NCH3) displays two vibronic band systems, which are attributed to the ionization of two-pair lowest-energy spin–orbit coupling states of N-methyl-ceraaziridine. Both metallaaziridines are three-membered metallacycles and formed by the thermodynamically and kinetically favorable concerted dehydrogenation of the amino group and one of the methyl groups. [ABSTRACT FROM AUTHOR]

Ln (Ln = La and Ce) atom reactions with methylamine are carried out in a pulsed-laser vaporization supersonic molecular beam source. A series of dehydrogenation species are observed with time-of-flight mass spectrometry, and the dehydrogenated Ln-containing species in the formula Ln(NCH3) are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and density functional theory and multiconfiguration spin–orbit coupling computations. The MATI spectrum of La(NCH3) consists of two vibronic band systems that are assigned to the ionization of the 2A1 ground state of the C3v isomer La(N–CH3) and the 2A′ ground state of the Cs isomer La(NH–CH2). The MATI spectrum of Ce(NCH3) also displays two band systems, which are attributed to the ionization of the low-energy spin–orbit coupling states of the C3v isomer Ce(N–CH3). Ln(N–CH3) is formed by the concerted dehydrogenation of the amino group, while La(NH–CH2) is formed by the dehydrogenation of both amino and methyl groups. Ce(NH–CH2) is presumably formed in the reaction based on the computational predictions but not observed by the spectroscopic measurements. [ABSTRACT FROM AUTHOR]

Ce atom reactions with ethylene, 2-butene, and isobutene are carried out in a pulsed laser vaporization molecule beam source. Ce-containing species are observed with time-of-flight mass spectrometry, and Ce(C4H6) is characterized with mass-analyzed threshold ionization (MATI) spectroscopy and relativistic quantum chemical calculations. Two structural isomers are identified for Ce(C4H6): one is the tetrahedronlike Ce[C(CH2)3] in C3v symmetry and the other is the five-membered metallocyclic Ce(CH2CHCHCH2) in Cs. The MATI spectrum of the C3v isomer exhibits two vibronic band systems separated by 88 cm−1, while that of the Cs isomer displays three split by 60 and 101 cm−1. The multiple band systems are attributed to spin-orbit splitting and vibronic transitions involving metal-hydrocarbon and hydrocarbon-based vibrations. The splitting in the C3v isomer arises from interactions of two triplet and two singlet states at the lowest energies, while each splitting in the Cs isomer involves two triplets and a singlet. Although the Ce atom has ground electron configuration 4f15d16s2, Ce valence electron configurations in both isomers are 4f16s1 in the neutral ground state and 4f1 in the ion. The remaining Ce 5d electrons in the isolated atom are spin paired in molecular orbitals that are a bonding combination between Ce 5dπ and hydrocarbon π* orbitals. [ABSTRACT FROM AUTHOR]

Group 6 metal–bis(mesitylene)sandwich complexes are produced by interactions between the laser-vaporizedmetal atoms and mesitylene vapor in a pulsed molecular beam source,identified by photoionization time-of-flight mass spectrometry, andstudied by pulsed-field ionization zero-electron kinetic energy spectroscopyand density functional theory calculations. Although transition metal–bis(arene)sandwich complexes may adopt eclipsed and staggered conformations,the group 6 metal–bis(mesitylene) complexes are determinedto be in the eclipsed form. In this form, rotational conformers withmethyl group dihedral angles of 0 and 60° are identified forthe Cr complex, whereas the 0° rotamer is observed for the Moand W species. The 0° rotamer is in a C2vsymmetry with the neutral ground stateof 1A1and the singly positive charged ion stateof 2A1. The 60° rotamer is in a Cisymmetry with the neutralground state of 1Agand the ion state of 2Ag. Partial conversion of the 60 to 0° rotameris observed from He to He/Ar supersonic expansion for Cr–bis(mesitylene).The unsuccessful observation of the 60° rotamer for the Mo andW complexes is the result of its complete conversion to the 0°rotamer in both He and He/Ar expansions. The adiabatic ionizationenergies of the 0° rotamers of the three complexes are in theorder of Cr–bis(mesitylene) < W–bis(mesitylene)

Single photon ionization (SPI) based on vacuum ultraviolet (VUV) lamps has been extensively investigated and applied due to its clean mass spectra as a soft ionization method. However, the photon energy of 10.6 eV and photon flux of 1011 photons s−1 of a commercial VUV lamp limits its range of ionizable analytes as well as its sensitivity. This work designs a chemical ionization focusing integrated (CIFI) ionization source time-of-flight mass spectrometry (TOFMS) based on a VUV lamp for the detection of volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs). The photoelectrons obtained from the VUV lamp via the photoelectric effect ionized the oxygen and water in the air to obtain the reagent ions. The ion–molecule-reaction region (IMR) is constituted by a segmented quadrupole that radially focuses the ions using a radio-frequency electric field. This significantly enhances the yield and transport efficiency of the product ions leading to a great improvement in sensitivity. As a result, a 44-fold and 1154-fold increase in the signal response for benzene and pentanal were achieved, respectively. To verify the reliability of the ionization source, the linear correspondence and repeatability of benzene and pentanal were investigated. Satisfactory dynamic linearity was obtained in the mixing ratio range of 5–50 ppbv, and the relative standard deviation (RSD) of inter-day reached 3.91% and 6.26%, respectively. Finally, the CIFI−TOFMS was applied to the determination of OVOCs, and the LOD of 12 types of OVOCs reached the pptv level, indicating that the ionization source has the potential for accurate and sensitive online monitoring of atmospheric OVOCs. [ABSTRACT FROM AUTHOR]

Ethane is the second largest component among natural gas, and the detection of ethane is an effective method for rapid identification of the leakage of the natural gas pipelines. In this work, a homogeneous sampling membrane inlet was developed and coupled with the homemade photoelectron ionization miniature time-of-flight mass spectrometer (PEI-mini-TOFMS) for in situ, on-line and highly sensitive ethane detection. The membrane area of the homogeneous sampling membrane inlet was increased from 490 mm2 to 1256 mm2, gaseous sample is injected from the top port and flowed through the membrane surface and out of the bottom two ports, with the three ports arranged in a triangular shape. The highest average flow velocity of the gas on the surface of the membrane reached 0.4 m s−1, and the optimal gas pressure in the PEI source was enhanced from 2.2 Pa to 4.0 Pa with this new design. The new design improved the comprehensive sensitivity of ethane by a factor of 3.0 compared with that of the traditional two-hole membrane inlet with the membrane area of 490 mm2. The semiconductor cold trap controlled the sample relative humidity (RH) at 10–12%, enabling direct sampling for highly sensitive analysis with RH as high as 70% and temperature from 7 °C to 40 °C. The quantitative range was 1–50 ppmv with a limit of detection (LOD, S/N = 3) lowered to 420 ppbv within 1 min, and zero humidity quantitative calibration with cold trap further reduced the relative standard deviation (RSD) of the signal intensities to 2.84%. The performance of the novel method developed in this work demonstrated a potential application on the above-ground natural gas pipelines leakage monitoring. [Display omitted] • A homogeneous sampling membrane inlet (HSMI) with three ports was developed to improve the enrichment efficiency. • The HSMI was coupled with the photoelectron ionization time-of-flight mass spectrometry (PEI-TOFMS) for ethane detection. • The HSMI improved ethane sensitivity by a factor of 3.0 compared with that of the traditional two-hole membrane inlet. • The ethane with different humidity can be quantitative analyzed by a home made semiconductor cold trap. • The MIPEI-mini-TOFMS has potential application in monitoring above-ground natural gas pipelines leakage. [ABSTRACT FROM AUTHOR]

Group 3 metal-aniline complexes, M(aniline) (M = Sc, Y, and La), are produced in a pulsed laser-vaporization molecular beam source, identified by photoionization time-of-flight mass spectrometry, and investigated by pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy and quantum chemical calculations. Adiabatic ionization energies and several low-frequency vibrational modes are measured for the first time from the ZEKE spectra. Metal binding sites and electronic states are determined by combining the ZEKE measurements with the theoretical calculations. The ionization energies of the complexes decrease down the metal group. An out-of-plane ring deformation mode coupled with an asymmetric metal-carbon stretch is considerably anharmonic. Although aniline has various possible sites for metal coordination, the preferred site is the phenyl ring. The metal binding with the phenyl ring yields syn and anti conformers with the metal atom and amino hydrogens on the same and opposite sides of the ring, respectively. The anti conformer is determined to be the spectral carrier. The ground electronic state of the anti conformer of each neutral complex is a doublet with a metal-based electron configuration of nd2(n + 1)s1, and the ground electronic state of each ion is a singlet with a metal-based electron configuration of nd2. The formation of the neutral complexes requires the nd2(n + 1)s1 ← nd1(n + 1)s2 electron excitation in the metal atoms. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel strategy to find absorbed constituents and metabolites of TCMs was proposed. [•] Absorption and metabolism of Paeoniae Radix Rubra were studied for the first time. [•] 13 new absorbed constituents of Paeoniae Radix Rubra were reported for the first time. [•] 90 new metabolites of PRR decoction were tentatively identified by LC–MS technique. [•] 22 new metabolites of paeoniflorin were reported for the first time. [Copyright &y& Elsevier]

Abstract: Calycosin and calycosin-7-O-β-d-glucoside are two main bioactive isoflavonoids in Astragali Radix. To profile the metabolites of calycosin in rat hepatic 9000× g supernatant incubation system and the metabolites of calycosin-7-O-β-d-glucoside in rat urine, high performance liquid chromatography with diode array detector and combined with electrospray ionization ion trap time-of-flight multistage mass spectrometry (HPLC–DAD–ESI-IT-TOF-MS n ) technique was used. Totally, 24 new in vitro metabolites of calycosin and 33 new in vivo metabolites of calycosin-7-O-β-d-glucoside were identified. Monoglucosylation, monopentosylation, demethylation, dehydroxylation, dimerization, and trimerization were found to be new in vitro metabolic reactions of calycosin; hydroxylation and hydrogenation were new metabolic reactions of calycosin-7-O-β-d-glucoside in vivo. The major metabolic reactions of calycosin in rat hepatic 9000× g supernatant incubation system were monohydroxylation on A-ring, dimerization (Cg), dimerization (Cg) and dehydroxylation; the major phase I metabolic reactions of calycosin-7-O-β-d-glucoside in rats were deglycosylation, hydroxylation, demethylation and dehydroxylation. Hydroxylation, dehydroxylation, and demethylation were common metabolic pathways to calycosin and calycosin-7-O-β-d-glucoside, and some of their metabolites formed through these reactions, such as 8-hydroxycalycosin (S10, M10), pratensein (5-hydroxycalycosin, S19, M27) and formononetin (S22, M28), daidzein (M22), 7,3′,4′-trihydroxyisoflavone (S13, aglycon of M3 and M8), equol (aglycon of M19 and M20) had been reported to have many bioactivities related to the pharmacological effects of calycosin and calycosin-7-O-β-d-glucoside. These findings would enhance understanding of the metabolism and real active forms of calycosin and calycosin-7-O-β-d-glucoside. [Copyright &y& Elsevier]