C 5 H x $\mathrm{C_5H_x}$ species are important intermediates in the formation of large carbonaceous molecules. Mass-selected threshold photoelectron spectra (TPES) of l-C 5 $_5$ H, HC 5 $_5$ H, and c-C 3 $_3$ H-CCH were recorded using double-imaging photoelectron-photoion coincidence spectroscopy. The TPES of l-C 5 $_5$ H and c-C 3 $_3$ H-CCH are reported for the first time. These transient species were generated in situ by hydrogen abstraction from cyclopropylacetylene and 1,3-pentadiyne by fluorine atoms in a discharge flow-tube reactor. Supported by ab initio calculations and Franck-Condon simulations, unambiguous assignments were achieved, enabling accurate determination of adiabatic ionization energies. The C 5 $_5$ H 2 $_2$ results show that hydrogen abstraction from structurally distinct precursors leads to similar isomeric distributions. More generally, the high-resolution TPES fingerprints reported here provide reliable discrimination between linear and cyclic C 5 $_5$ H x $_x$ isomers, which is not possible using only photoion yields, offering robust benchmarks for identifying reactive hydrocarbon intermediates in combustion and astrochemical environments.

Interpreting the spectra of mixtures of different isomers is a persistent challenge in gas‐phase ion spectroscopy, particularly when dealing with large molecules. The ability of our new instrument to obtain spectroscopic information on carbon‐rich molecular ions in an isomer‐selected fashion is demonstrated. This approach relies on coupling drift‐tube ion mobility and mass spectrometry with spectroscopic interrogation in a cryogenic 3D Paul trap. The instrument provides the possibility to employ two action spectroscopy techniques: two‐color resonance‐enhanced photodissociation and messenger‐tagging spectroscopy, which together provide a versatile experimental framework for obtaining spectroscopic fingerprints of isomer‐selected molecular ions. The method is illustrated on the example of C14+ and Ca@C60+. Additionally, the first demonstration of the feasibility of messenger‐tagging spectroscopy using helium as messenger in a 3D Paul trap is reported.

The photoabsorption and photoionization spectra of molecular nitrogen, N2 , near the first ionisation threshold display numerous intense resonances that have not been satisfactorily assigned to date. Principal among these is a pair of broad resonances between 126,200 and 126,600 cm -1 commonly referred to as the "cathedral" bands. Here, we present new double-resonance photoionization spectra in this region recorded via the a '' 1 Sigma g+,v '=0 intermediate state as well as new high-resolution, vacuum-ultraviolet photoabsorption spectra of 14 N 2 , 14 N 15 N, and 15 N 2 to provide additional insight into the assignment of these features. Progress towards a fully consistent interpretation of the existing data on these bands is discussed, and a route towards a comprehensive description of the N2 absorption spectrum up to the B 2 Sigma u+ state of N 2+ is proposed.

Complementing our recent work on ammonia [Pratt et al., J. Mol. Spectrosc. 2023, 396, 111810], we here present new high-resolution photoabsorption spectra of deuterated ammonia, ND3, spanning the region between 59,000 and 93,000 cm(-1). This region extends from just above the Franck-Condon envelope for the A(1)A(2)'' <- X(1)A(1)' transition to well above the ND3+ X+ (2)A(2)'' ionization threshold. The absolute photoabsorption cross sections were recorded at room temperature using the Fourier transform spectrometer at the Synchrotron SOLEIL with a measured spectral resolution of 0.22 cm(-1), which is a factor of 10-100 times higher than in any previously reported broadband spectrum of ND3. The spectra reveal partially resolved rotational structure in several different vibrational progressions, which allows the reassignment of some of the higher energy bands, enabling proposed assignments for the P1 and P2 progressions reported by Wu et al. [J. Chem. Phys. 2007, 127, 154311] and an expanded appraisal of the pattern of lower-lying Rydberg states of ammonia.

We report a study of the diazabicyclo[2.2.2]octane (DABCO) molecule photoionized using VUV synchrotron radiation in combination with an ion–electron coincidence spectrometer. We determine accurately the adiabatic ionization energy to 7.199±0.006 eV. Two vibrational progressions of DABCO cation ground state are resolved at 847 cm^-1±27 cm^-1 and 1257 cm^-1±67 cm^-1, which we assign to modes of e' symmetry. Analysis of the photoelectron angular distribution shows that the anisotropy parameter depends on the vibrational excitation. This dependence of the β parameter with the vibrational excitation is attributed to the scattering of the outgoing wavefunction mediated by high-lying Rydberg states.

The hydration of the phenylium ion (C6H5+) is investigated to determine whether the most abundant product structure is best described as an oxonium (O‐protonated phenol) or carbenium (ring‐protonated phenol) ion. Using a combination of infrared multiple‐photon dissociation spectroscopy at the FELIX facility, collision‐induced dissociation experiments, and quantum chemical calculations, we have characterized the reaction products formed upon the addition of water to phenylium. The IR fingerprint of the hydrated ion reveals dominant spectral features consistent with carbenium isomers, particularly the ortho and para forms, rather than the oxonium isomer. Reactivity measurements and branching ratios of the reaction between water and C6H5+ produced by vacuum ultraviolet (VUV) dissociative photoionization of nitrobenzene at the SOLEIL synchrotron facility, as a function of internal energy show that protonated phenol forms efficiently in the gas phase. Computational modeling of the potential energy surface supports the preferential formation of carbenium structures and maps the key isomerization and dissociation pathways.

species are important intermediates in the formation of large carbonaceous molecules. Mass-selected threshold photoelectron spectra (TPES) of l-CH, HCH, and c-CH-CCH were recorded using double-imaging photoelectron-photoion coincidence spectroscopy. The TPES of l-CH and c-CH-CCH are reported for the first time. These transient species were generated in situ by hydrogen abstraction from cyclopropylacetylene and 1,3-pentadiyne by fluorine atoms in a discharge flow-tube reactor. Supported by ab initio calculations and Franck-Condon simulations, unambiguous assignments were achieved, enabling accurate determination of adiabatic ionization energies. The CH results show that hydrogen abstraction from structurally distinct precursors leads to similar isomeric distributions. More generally, the high-resolution TPES fingerprints reported here provide reliable discrimination between linear and cyclic CH isomers, which is not possible using only photoion yields, offering robust benchmarks for identifying reactive hydrocarbon intermediates in combustion and astrochemical environments.

Complementing our recent work on ammonia [Pratt et al., J. Mol. Spectrosc. 2023, 396, 111810], we here present new high-resolution photoabsorption spectra of deuterated ammonia, ND3, spanning the region between 59,000 and 93,000 cm-1. This region extends from just above the Franck-Condon envelope for the à 1A2″ ← X̃ 1A1' transition to well above the ND3+ X̃+ 2A2″ ionization threshold. The absolute photoabsorption cross sections were recorded at room temperature using the Fourier transform spectrometer at the Synchrotron SOLEIL with a measured spectral resolution of 0.22 cm-1, which is a factor of 10-100 times higher than in any previously reported broadband spectrum of ND3. The spectra reveal partially resolved rotational structure in several different vibrational progressions, which allows the reassignment of some of the higher energy bands, enabling proposed assignments for the P1 and P2 progressions reported by Wu et al. [J. Chem. Phys. 2007, 127, 154311] and an expanded appraisal of the pattern of lower-lying Rydberg states of ammonia.

Interpreting the spectra of mixtures of different isomers is a persistent challenge in gas‐phase ion spectroscopy, particularly when dealing with large molecules. The ability of our new instrument to obtain spectroscopic information on carbon‐rich molecular ions in an isomer‐selected fashion is demonstrated. This approach relies on coupling drift‐tube ion mobility and mass spectrometry with spectroscopic interrogation in a cryogenic 3D Paul trap. The instrument provides the possibility to employ two action spectroscopy techniques: two‐color resonance‐enhanced photodissociation and messenger‐tagging spectroscopy, which together provide a versatile experimental framework for obtaining spectroscopic fingerprints of isomer‐selected molecular ions. The method is illustrated on the example of and . Additionally, the first demonstration of the feasibility of messenger‐tagging spectroscopy using helium as messenger in a 3D Paul trap is reported.

The molecule, 2-cyanoindene, C _10 H _7 N (2CNI) is the only cyanosubstituted polycyclic aromatic hydrocarbon (PAH) detected in space, for which the hydrocarbon counterpart, indene, has also been observed in the same astrochemical environment—the molecular cloud TMC-1. In this study, based on experiments in two different laboratories, the collision and radiation-driven dissociation and cooling dynamics of the 2-cyanoindene monocations are investigated using one of the electrostatic ion-beam storage rings of the DESIREE facility, and the DESIRS beamline at the SOLEIL synchrotron radiation facility. The storage ring experiments quantify the balance between fragmentation and radiative cooling of the stored cations, while the synchrotron experiments characterize dissociation channels from the vacuum ultraviolet-induced dissociative photoionization of the neutrals. Recurrent fluorescence is shown to play an important role in the radiative stabilization of 2CNI ^+ . The results from both sets of experiments are combined to obtain a self-consistent set of microcanonical rate coefficients for dissociation and radiative cooling that completely describe the near-dissociation threshold dynamics of 2CNI ^+ across the microseconds-seconds time range. This timescale is suitable for incorporation into astrochemical models of PAH growth and destruction lifecycles. This study extends its findings to different astrochemical environments by simulating the extent of fragmentation and the cascade emission spectra of 2CNI ^+ under varying interstellar radiation fields. These results indicate that radiative cooling enhances the resilience of 2-cyanoindene to harsh radiation conditions, suggesting that small cyano-PAHs may survive longer than previously assumed in a wider range of astrochemical environments, extending beyond cold, dark molecular clouds.

Aims. Our goal is to use the first detection of CH+ and CH3+ infrared rovibrational emission in the Orion Bar and in the protoplanetary disk d203-506 to probe their formation and excitation mechanisms and constrain the physico-chemical conditions of the environment. Methods. We used spectro-imaging acquired using both the NIRSpec and MIRI-MRS instruments on board JWST to study the infrared CH+ and CH3+ spatial distribution at very small scales (down to 0.1 '') and compared it to excited H-2 emission. We studied their excitation in detail, and in the case of CH+, we compared the observed line intensities with chemical formation pumping models based on recent quantum dynamical calculations. Throughout this study, we compare the emission of these molecules in two environments: the Bar a photodissociation region - and a protoplanetary disk (d203-506), both of which are irradiated by the Trapezium cluster. Results. We detected CH+ and CH3+ vibrationally excited emission both in the Bar and d203-506. These emissions originate from the same region as highly excited H-2 (high rotational and rovibrational levels) and correlate less with the lower rotational levels of H-2 (J ' < 5) or the emission of aromatic and aliphatic infrared bands. Our comparison between the Bar and d203-506 revealed that both CH+ and CH3+ excitation and/or formation are highly dependent on gas density. The excitation temperature of the observed CH+ and CH3+ rovibrational lines is around T similar to 1500 K in the Bar and T similar to 800 K in d203-506. Moreover, the column densities derived from the rovibrational emission are less than 0.1% of the total known (CH+) and expected (CH3+) column densities. These different results show that CH+ and CH3+ level populations strongly deviate from local thermodynamical equilibrium. The CH+ rovibrational supra-thermal emission (v = 1 and v = 2) can be explained by chemical formation pumping with excited H-2 via C+ + H-2* = CH+ + H. The difference in the population distribution of the H-2* energy levels between the Orion Bar and d203-506 then result in different excitation temperatures. These results support a gas phase formation pathway of CH+ and CH3+ via successive hydrogen abstraction reactions. However, we do not find any evidence of CH3+ emission in the JWST spectrum, which may be explained by the fact its spectroscopic signatures could be spread in the JWST spectra. Finally, the observed CH+ intensities coupled with a chemical formation pumping model provide a diagnostic tool to trace the local density. Conclusions. Line emission from vibrationally excited CH+ and CH3+ provides new insight into the first steps of hydrocarbon gas-phase chemistry in action. This study highlights the need for extended molecular data of detectable molecules in the interstellar medium in order to analyze the JWST observations.

Pulsed-field-ionisation zero-kinetic-energy photoelectron spectrum of silylidyne radical (SiH) has been recorded in the vicinity of its first ionisation threshold at high and medium spectral resolutions using a laser-based experiment. The obtained rotationally-resolved spectrum of the $ \mathrm {X}<^>+\,<^>1\Sigma <^>+ \leftarrow \mathrm {X}\,<^>2\Pi _{\varOmega } $ X+1 Sigma+<- X2 Pi Omega ( $ \varOmega =1/2 $ Omega=1/2 and 3/2) photoionising transitions allowed a precise determination of the corresponding adiabatic ionisation energy which refines the recent results obtained by Chen et al. J. Chem. Phys. 157, 014303 (2022) using a synchrotron-based experiment at lower spectral resolution.

Ammonium salts are increasingly suspected to play an important role in astrochemistry, as both a reservoir, particularly of sulfur and nitrogen, and a potential source of complex molecules, in spite of the lack of knowledge on their sublimation process and products. We have studied the sublimation of four ammonium salts using mass-selected photoelectron spectroscopy coupled to vacuum ultraviolet synchrotron radiation to identify most of the sublimation products. We show that, if proton transfer yields stable products without rearrangement, leading to NH3 or CH3NH2, this route will be favored. Furthermore, we suggest that the sublimation of salts could lead to the formation of complex molecules, such as formamide, and also constitute a possible route for the formation of isonitriles.

Silicon monosulfide (SiS) is an important molecule in astrochemistry likely linked to dust production through the formation of sulfide particles. This work presents the vacuum ultraviolet photoionisation of SiS formed in situ in a discharge flow reactor, in particular the threshold photoelectron spectrum covering the first three electronic states of the SiS+ cation. The rich vibronic structure is assigned with the support of ab initio calculations and a spin orbit coupling constant of -323 ± 41 cm-1 is measured for the ground state. Adiabatic ionisation energies (10.453 ± 0.003, 10.515 ± 0.003 and 13.802 ± 0.003 eV for the ground, first and second excited state, respectively) and vibrational frequencies are also extracted from the spectra, and combined with the existing thermochemical values yields the SiS+ dissociation energy (4.09 ± 0.01 eV).

The study employs threshold photoelectron spectroscopy (TPES) using vacuum ultraviolet synchrotron radiation to refine spectroscopic constants and fundamental energies of monosulfur monofluoride (SF). High-precision adiabatic ionization energy (AIE) measurements are achieved that could serve as benchmarks for future calculation of heat of formation of SF and its ionized form, SF+. Experimental methods utilized include a microwave discharge reactor coupled with synchrotron-based spectroscopy, providing TPES and photoion yield spectra of SF. Analysis supported by ab initio calculations enables the determination of key spectroscopic parameters, including vibrational constants and ionization thresholds. The resulting AIE of 10.195(5) eV is the most accurate value to date, enhancing the reliability of thermochemical databases.

Distinguishing the chemical reactivity of isomers is a fundamental challenge in chemistry, particularly in cluster chemistry, where the number of possible structures increases dramatically with cluster size. This study presents a novel approach for measuring the kinetics of ion‐molecule reactions of laser‐ablated species in an isomer‐specific fashion. This is achieved by combining drift‐tube ion mobility with mass spectrometry, enabling shape selection prior to investigating the chemical reactivity of species of interest. First, the capability of obtaining reaction rate coefficients by studying the nucleophilic addition reactions of small monocyclic carbon rings (, , and ) with pyridine, comparing the results with previously reported values is validated. Then the ability to determine isomer‐specific reaction rate coefficients using the cluster, where multiple isomers coexist is demonstrated. This highlights the potential of our new instrument for accurately characterizing isomer‐specific reactivities in complex chemical systems.

Endohedral metallofullerenes (EMFs) are a unique class of hybrid molecules formed by encapsulating metal atoms within carbon cages (fullerenes), giving rise to distinctive properties that differ from empty fullerenes. Extensive research has focused on optimizing the synthesis, extraction, isolation, and characterization of EMFs, along with investigating their physicochemical properties and potential applications in areas such as electronics, photovoltaics, biomedicine, and materials science. Here, the use of a laser vaporization source combined with ion mobility and mass spectrometry is demonstrated to characterize and isolate EMF structures, enabling further investigation of their gas-phase chemical properties. This approach is illustrated through a comparative study of the reactivity of empty carbon cages and calcium EMFs in the nucleophilic addition of pyridine.