Breakdown Diagram Research Articles

Photoionization and Dissociative Photoionization of Acetaldehyde in the 10.0-13.7 eV Range by Synchrotron Photoelectron Photoion Coincidence Spectroscopy.

Photoionization and dissociative photoionization of acetaldehyde (CH3CHO) in the 10.0-13.7 eV energy range are studied by using synchrotron radiation double imaging photoelectron photoion coincidence spectroscopy (i2PEPICO). The X2A' and A2A" electronic states of CH3CHO+ as well as the Franck-Condon gap region between these two states have been populated with several vibrational sequences and assigned in the high-resolution slow photoelectron spectrum (SPES). The adiabatic ionization energies (AIEs) of the X2A' and A2A" states are measured at 10.228±0.006 and 12.52±0.05 eV, respectively. The present results show that the X2A' state is a stable state while the A2A" state is fully dissociative to produce CH3CO+, CHO+ and CH4 + fragment ions. The 0 K appearance energies (AE0K) of CH3CO+ and CHO+ fragment ions are determined through the modeling of the breakdown diagram, i. e., AE0K(CH3CO+)=10.89±0.01 eV (including a reverse barrier of ~0.19 eV) and AE0K(CHO+)=11.54±0.05 eV. In addition, the dissociation mechanisms of CH3CHO+ including statistical dissociation, direct bond breaking and isomerization are discussed with the support of the calculated dissociation limits and transition state energies.

Photoelectron spectrum and breakdown diagram of ethanolamine: conformers, excited states, and thermochemistry.

Advanced theoretical methodologies and photoelectron photoion coincidence spectroscopy were used to investigate the photoionization of ethanolamine in the 8-18 eV energy range. We identified the low-lying cation conformers and the excited cation electronic states after vertical excitation from the most stable neutral conformer computationally. The TPES is composed of broad, structureless bands because of unfavorable Franck-Condon factors for origin transitions upon ionization, populating the D0-D7 cationic states from the most stable neutral conformer, g'Gg'. The adiabatic ionization energy of ethanolamine is calculated at 8.940 ± 0.010 eV, and the 0 K appearance energies of aminomethylium, NH2CH2+ (+CH2OH), and methyleneammonium, NH3CH2+ (+H2CO), are determined experimentally to be 9.708 ± 0.010 eV and 9.73 ± 0.03 eV, respectively. The former is used to re-evaluate the ethanolamine enthalpy of formation in the gas and liquid phases as ΔfH⊖298K[NH2(CH2)2OH, g] = -208.2 ± 1.2 kJ mol-1 and ΔfH⊖298K[NH2(CH2)2OH, l] = -267.8 ± 1.2 kJ mol-1. This represents a substantial correction of the previous experimental determination and is supported by ab initio calculations.

Enlightening salt: enthalpy of formation of gaseous sodium chloride by photoelectron photoion coincidence spectroscopy

An in-vacuum flash pyrolysis microreactor was used to seed a molecular beam with gaseous sodium chloride. The vapour was ionised with tuneable synchrotron vacuum ultraviolet radiation to determine the 0 K appearance energy of the sodium cation from sodium chloride using photoelectron photoion coincidence spectroscopy. In addition to the Na+ and NaCl+ peaks, Na2Cl+ was also observed in the mass spectrum, as a tracer for gaseous (NaCl)2. Larger clusters were not observed. The breakdown diagram showed that the monomer underwent significant collisional cooling in the molecular beam, tentatively because of the increased stagnation pressure in the reactor. It also yielded an Na+ appearance energy of E 0 = 9.351 ± 0.007 eV. By the ion cycle, this leads to D 0(NaCl) = 406.4 ± 0.7 kJ mol−1 and Δf H o⦵ 0K(NaCl(g)) = −179.0 ± 1.0 kJ mol−1, which agree with but are better defined than the previous values. This enthalpy of formation is independent of the crystalline phase, and therefore confirms the literature sublimation enthalpy, as well.

Photoelectron spectroscopy and dissociative photoionization of fulminic acid, HCNO.

We report a joint experimental and computational study of the photoelectron spectroscopy and the dissociative photoionization of fulminic acid, HCNO. The molecule is of interest to astrochemistry and astrobiology as a potential precursor of prebiotic molecules. Synchrotron radiation was used as the photon source. Dispersive photoelectron spectra were recorded from 10 to 22eV, covering four band systems in the HCNO cation, and an ionization energy of 10.83eV was determined. Transitions into the Renner-Teller distorted X+2Π state of the cation were simulated using wavepacket dynamics based on a vibronic coupling Hamiltonian. Very good agreement between experiment and theory is obtained. While the first excited state of the cation shows only a broad and unstructured spectrum, the next two higher states exhibit a well-resolved vibrational progression. Transitions into the excited electronic states of HCNO+ were not simulated due to the large number of electronic states that contribute to these transitions. Nevertheless, a qualitative assignment is given, based on the character of the orbitals involved in the transitions. The dissociative photoionization was investigated by photoelectron-photoion coincidence spectroscopy. The breakdown diagram shows evidence for isomerization from HCNO+ to HNCO+ on the cationic potential energy surface. Zero Kelvin appearance energies for the daughter ions HCO+ and NCO+ have been derived.

Threshold photoelectron spectroscopy and dissociative photoionization of benzonitrile.

The threshold photoionization and dissociative ionization of benzonitrile (C6H5CN) were studied using double imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy at the Vacuum Ultraviolet (VUV) beamline of the Swiss Light Source (SLS). The threshold photoelectron spectrum was recorded from 9.6 to 12.7 eV and Franck-Condon simulations of ionization into the ionic ground state, X̃+, as well as the B̃+ and C̃+ states were performed to assign the observed vibronic structures. The adiabatic ionization energies of the X̃+, B̃+ and C̃+ states are determined to be (9.72 ± 0.02), (11.85 ± 0.03) and, tentatively, (12.07 ± 0.04) eV, respectively. Threshold ionization mass spectra were recorded from 13.75 to 19.75 eV and the breakdown diagram was constructed by plotting the fractional abundances of the parent ion and ionic dissociation products as a function of photon energy. The seven lowest energy dissociative photoionization channels of benzonitrile were found to yield CN˙ + c-C6H5+, HCN + C6H4˙+, C2H4 + HC5N˙+, HC3N + C4H4˙+, H2C3N˙ + C4H3+, CH2CHCN + C4H2˙+ and H2C4N˙ + c-C3H3+. HCN loss from the benzonitrile cation is the dominant dissociation channel from the dissociation onset of up to 18.1 eV and CH2CHCN loss becomes dominant from 18.1 eV and up. We present extensive potential energy surface calculations on the C6H5CN˙+ surface to rationalize the detected products. The breakdown diagram and time-of-flight mass spectra are fitted using a Rice-Ramsperger-Kassel-Marcus statistical model. Anchoring the fit to the CBS-QB3 result (3.42 eV) for the barrier to HCN loss, we obtained experimental dissociation barriers for the products of 4.30 eV (CN loss), 5.53 eV (C2H4 loss), 4.33 eV (HC3N loss), 5.15 eV (H2C3N loss), 4.93 eV (CH2CHCN loss) and 4.41 eV (H2C4N loss). We compare our work to studies of the electron-induced dissociative ionization of benzonitrile and isoelectronic phenylacetylene (C8H6), as well as the VUV-induced dissociation of protonated benzonitrile (C6H5CNH+). Also, we discuss the potential role of barrierless association reactions found for some of the identified fragments as a source of benzonitrile(˙+) in interstellar chemistry and in Titan's atmosphere.

Branching ratios in the dissociative photoionization of iodomethane by photoelectron photoion coincidence.

Iodomethane yields ten fragment ions after valence photoionization, in part by multiple dissociation pathways for each, thanks to a plethora of electronic states available in the parent ion as well as in the fragments. The comprehensive breakdown diagram from 11 eV to the double ionization onset, i.e., 26.7 eV, is recorded at high resolution using double imaging photoelectron photoion coincidence spectroscopy with synchrotron vacuum ultraviolet radiation. Based on fragment ion groupings, the changing branching ratios between these groups and between fragment ions within each group, as well as ancillary thermochemistry, we provide an overview of the dissociation pathways at play. Statistical and impulsive dissociations are identified using kinetic energy release analysis. Finally, a newly observed regime change is discussed in double ionization, whereby coincident H+ + I+ formation dominates over a 4 eV photon energy range, outcompeting the normally prevailing CH3+ + I+ channel.

Structures and dissociation of iron porphyrin complexes by ion mobility and collision-induced dissociation mass spectrometry

A combination of ion mobility mass spectrometry (IMS-MS), collision-induced dissociation (CID), Rice–Ramsperger–Kassel–Marcus modeling, and computational chemistry was used to determine the structure and unimolecular chemistry of dimeric and trimeric sulfonated meso-tetraphenylporphyrins with negative charges from −2 to −5. By comparing experimental collision cross sections obtained from calibrated IMS drift times with calculated cross sections for the lowest energy calculated structures, it was confirmed that dimer species have a bridged structure where the two monomers are connected through iron–sulfonic interactions. Dimer species with the charge states −4 and −5 dissociate into two monomer units where the charge is distributed between the monomers. Dimers with lower charge states also lose neutral SO2 and SO3 groups. For trimeric species with charge states of −3 and −4, IMS identifies three and two isomers, respectively. It was confirmed that the −4 charged trimer isomers consist of one with three stacked monomers and one in which the third monomer unit is connected to a stacked dimer via two iron–sulfonic bonds (bridged/stacked). Both yielded the same CID breakdown diagram confirming that the two isomers likely interconvert prior to dissociation. The significantly larger density of states of the bridged–stacked structure compared with the stacked structure means the former is likely the reactive configuration.

OPTIMALISASI BIAYA PELAKSANAAN PEMBANGUNAN ADMINISTRATION BUILDING MENGGUNAKAN METODE VALUE ENGINEERING

Value Engineering is a multidisciplinary-based systematic approach that is carried out creatively,innovatively and systematically to find a functional balance between cost, reliability and performance toachieve the concept of value for money. In value engineering there are six stages. The information stagecarried out 2 analyzes, namely cost breakdown and Pareto diagram analysis, resulting in the largestwork being owned by concrete work with a weight of 37% and a weight of 28% of floor slab work fromthe total concrete work. The function analysis stage produces 1 primary function and 4 secondaryfunctions. The creative stage produces 3 creative ideas, namely the Conventional Method (PA-1),Floordeck and Wiremesh Method (PA-2), and Hollow Core Slab Method (PA-3). The evaluation stageresulted in 2 creative ideas that passed. In the development stage, several calculations are carried outthat support all creative ideas. In the evaluation criteria stage, each alternative choice is assessed withthe help of the Expert Choice application, resulting in a total PA-2 value of 20% greater than PA-1. Thecalculation of the floor slab design results in the serviceability of PA-2 being 12.67% higher than that ofPA-1. PA-1's NPV is 5% greater than PA-2's. The PA-2 index value is 2.17 smaller than PA-1. The use ofPA-2 can save RAB of IDR 101,372,430.00 or 5%.

VUV photoprocessing of oxygen-containing polycyclic aromatic hydrocarbons: iPEPICO study of the unimolecular dissociation of ionized benzofuran

Oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) are potential contributors to the 11.3 µm band in interstellar observations. To further explore their role in the interstellar medium, we investigated their fate after photoprocessing by VUV radiation; in particular, we studied the dissociative photoionization of the simplest OPAH, benzofuran, with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. Ionized benzofuran dissociates by loss of CO, followed by a sequential H-atom loss. The parallel HCO-loss channel, leading to the same bicyclic C7H5+ fragment ion, is not competitive at low excess energies above the ionization threshold. However, the collision-induced dissociation tandem mass spectrometry results suggest that CO and HCO may be formed in parallel at higher energies. A Rice–Ramsperger–Kassel–Marcus fragmentation model reproduced the iPEPICO data well, assuming the initial 1,2-H shift transition state to be rate determining to CO loss. The breakdown diagram and the measured dissociation rates agreed well at the CBS-QB3-calculated activation energy of 2.99 eV, which could be relaxed to 3.25 eV, and only a slight adjustment of the ab initio activation entropy. The model barrier to sequential H loss is larger than the computed H-loss threshold and the breakdown diagram rises less steeply than predicted, which indicates suprastatistical kinetic energy release after the tight H-transfer transition state of the first step. HCO cleavage is possible after a ring-opening transition state, which is looser than and isoenergetic with the CO-loss transition state. However, a subsequent ring formation transition state at 3.85 eV is moderately tight, which suppresses HCO loss at low excess energies.

Continuous Pyrolysis Microreactors: Hot Sources with Little Cooling? New Insights Utilizing Cation Velocity Map Imaging and Threshold Photoelectron Spectroscopy.

Resistively heated silicon carbide microreactors are widely applied as continuous sources to selectively prepare elusive and reactive intermediates with astrochemical, catalytic, or combustion relevance to measure their photoelectron spectrum. These reactors also provide deep mechanistic insights into uni- and bimolecular chemistry. However, the sampling conditions and effects have not been fully characterized. We use cation velocity map imaging to measure the velocity distribution of the molecular beam signal and to quantify the scattered, rethermalized background sample. Although translational cooling is efficient in the adiabatic expansion from the reactor, the breakdown diagrams of methane and chlorobenzene confirm that the molecular beam component exhibits a rovibrational temperature comparable with that of the reactor. Thus, rovibrational cooling is practically absent in the expansion from the microreactor. The high rovibrational temperature also affects the threshold photoelectron spectrum of both benzene and the allyl radical in the molecular beam, but to different degrees. While the extreme broadening of the benzene TPES suggests a complex ionization mechanism, the allyl TPES is in fact consistent with an internal temperature close to that of the reactor. The background, room-temperature spectra of both are superbly reproduced by Franck-Condon simulations at 300 K. On the one hand, this leads us to suggest that room-temperature reference spectra should be used in species identification. On the other hand, analysis of the allyl iodide pyrolysis data shows that iodine atoms often recombine to form molecular iodine on the chamber surfaces. Such sampling effects may distort the chemical composition of the scattered background with respect to the molecular beam signal emanating directly from the reactor. This must be considered in quantitative analyses and kinetic modeling.

Photoelectron Spectroscopy of the Water Dimer Reveals Unpredicted Vibrational Structure.

Hydrogen bonds and proton transfer reactions can be considered as being at the very heart of aqueous chemistry and of utmost importance for many processes of biological relevance. Nevertheless, these processes are not yet well understood, even in seemingly simple model systems like small water clusters. We present a study of the photoelectron spectrum of the water dimer, revealing previously unresolved vibrational structure with 10-30 meV (80-242 cm-1) typical splitting, in disagreement with a previous theoretical photoionization study predicting an apparent main vibrational progression with an ∼130 meV spacing [Kamarchik et al.; J. Chem. Phys. 2010, 132, 194311]. The observed vibrational structure and its deviation from the theoretical prediction is discussed in terms of known difficulties with calculations of strongly coupled anharmonic systems involving large amplitude motions. Potential contributions of the nonzero vibrational energy of the neutral water dimer at a finite experimental internal temperature are addressed. The internal temperature is estimated from the breakdown diagram associated with the dissociative ionization of the water dimer to be around to 130 K. This analysis also provides two additional, independently measured values for the 0 K appearance energy of the hydronium ion (H3O+) from dissociative ionization of the water dimer.

Valence Photoionization and Energetics of Vanillin, a Sustainable Feedstock Candidate.

We studied the valence photoionization of vanillin by photoelectron photoion coincidence spectroscopy in the 8.20-19.80 eV photon energy range. Vertical ionization energies by EOM-IP-CCSD calculations reproduce the photoelectron spectral features. Composite method calculations and Franck-Condon simulation of the weak, ground-state band yield the adiabatic ionization energy of the most stable vanillin conformer as 8.306(20) eV. The lowest energy dissociative photoionization channels correspond to hydrogen atom, carbon monoxide, and methyl losses, which form the dominant C8H7O3+ (m/z 151) and the less intense C7H8O2+ (m/z 124) and C7H5O3+ (m/z 137) fragment ions in parallel dissociation channels at modeled 0 K appearance energies of 10.13(1), 10.40(3), and 10.58(10) eV, respectively. On the basis of the breakdown diagram, we explore the energetics of sequential methyl and carbon monoxide loss channels, which dominate the fragmentation mechanism at higher photon energies. The 0 K appearance energy for sequential CO loss from the m/z 151 fragment to C7H7O2+ (m/z 123) is 12.99(10) eV, and for sequential CH3 loss from the m/z 123 fragment to C6H4O2+ (m/z 108), it is 15.40(20) eV based on the model. Finally, we review the thermochemistry of the bi- and trifunctionalized benzene derivatives guaiacol, hydroxybenzaldehyde, anisaldehyde, and vanillin. On the basis of isodesmic functional group exchange reactions, we propose new enthalpies of formations, among them ΔfH°298K(vanillin, g) = -383.5 ± 2.9 kJ mol-1. These mechanistic insights and ab initio thermochemistry results will support analytical works to study lignin conversion involving vanillin.

Using a Fork as a Hairbrush: Investigating Dual Routes to Release from Functional Fixedness

AbstractFunctional fixedness involves difficulty with conceptualizing creative object uses. When it obstructs problem‐solving, individuals must reframe their approach. We examined how different training techniques—chunk decomposition (i.e., considering an object’s basic parts and physical properties) and constraint relaxation (i.e., considering an object’s different functions)—might rely upon different routes to creative reframing. Additionally, we investigated how different forms of cognitive load interact with these dual routes. Participants learned one of three techniques. Chunk decomposition participants created object breakdown diagrams; constraint relaxation participants created object functions lists; and free association (control) participants wrote a word that they associated with each of several concrete nouns. After training, participants attempted to solve five functional fixedness problems. E1 investigated how increasing germane cognitive load via either direct or indirect prompting affected training transfer. Experiment 2 investigated how reducing extraneous cognitive load by providing no transfer instructions and using an eye‐closure strategy. Across both experiments, results supported differences in accuracy and response latency by training. However, chunk decomposition and constraint relaxation did not follow the same pattern, suggesting different mechanisms of the effect. We discuss possible applications to increase innovation in real‐world domains such as education, business, and engineering.

A guinea pig for conformer selectivity and mechanistic insights into dissociative ionization by photoelectron photoion coincidence: fluorocyclohexane.

We studied fluorocyclohexane (C6H11F, FC6) by double imaging photoelectron photoion coincidence spectroscopy in the 9.90-13.90 eV photon energy range. The photoelectron spectrum can identify species isomer and, in this case, even conformer selectively. Ab initio results indicated that the axial conformer has two, close-lying cation electronic states. With the help of Franck-Condon simulations of the vibrational fine structure, we determined the origin of three transitions, (i) axial FC6 → axial FC6+ of C1 symmetry (X[combining tilde]+, A'' in CS), (ii) equatorial FC6 → equatorial FC6+ of C1 symmetry (X[combining tilde]+, A'' in CS), and (iii) axial FC6 → A' axial FC6+ of CS symmetry (Ã+) as 10.12 ± 0.01, 10.15 ± 0.01 and 10.15 ± 0.02 eV, respectively. At slightly higher energies, the FC6 cation starts fragmenting by HF loss (E0 = 10.60 eV), followed by sequential CH3 (E0 = 10.71 eV) or C2H4 (E0 = 11.06 eV) loss. Surprisingly, the methyl-loss step has an effective barrier of only 0.11 eV, and yet it is a slow process at threshold. Based on the statistical model, this is explained by isomerization and stabilization of the C6H10+ intermediate. The highest energy channel observed, vinyl fluoride (C2H3F) loss yielding C4H8+ appears in the breakdown diagram at 12 eV, which agrees with the computed threshold to cyclobutane cation formation. However, the model predicted a ca. 1 eV competitive shift for this parallel channel, i.e., an E0 = 11.23 eV. This led us to explore the potential energy surface to find a lower-lying fragmentation channel including H-transfer steps. Rate constant measurements and statistical modeling thus yield fundamental insights into the reaction mechanism beyond what is immediately seen in the mass spectra.

Valence Photoionization of Thymine: Ionization Energies, Vibrational Structure, and Fragmentation Pathways from the Slow to the Ultrafast.

The photoionization of thymine has been studied by using vacuum ultraviolet radiation and imaging photoelectron photoion coincidence spectroscopy after aerosol flash vaporization and bulk evaporation. The two evaporation techniques have been evaluated by comparison of the photoelectron spectra and breakdown diagrams. The adiabatic ionization energies for the first four electronic states were determined to be 8.922±0.008, 9.851±0.008, 10.30±0.02, and 10.82±0.01 eV. Vibrational features have been assigned for the first three electronic states with the help of Franck-Condon factor calculations based on density functional theory and wave function theory vibrational analysis within the harmonic approximation. The breakdown diagram of thymine, as supported by composite method ab initio calculations, suggests that the main fragment ions are formed in sequential HNCO-, CO-, and H-loss dissociation steps from the thymine parent ion, with the first step corresponding to a retro-Diels-Alder reaction. The dissociation rate constants were extracted from the photoion time-of-flight distributions and used together with the breakdown curves to construct a statistical model to determine 0 K appearance energies of 11.15±0.16 and 11.95±0.09 eV for the m/z 83 and 55 fragment ions, respectively. These results have allowed us to revise previously proposed fragmentation mechanisms and to propose a model for the final, nonstatistical H-loss step in the breakdown diagram, yielding the m/z 54 fragment ion at an appearance energy of 13.24 eV.

Trifluoroacetic Acid and Trifluoroacetic Anhydride Radical Cations Dissociate near the Ionization Limit.

The threshold photoelectron spectra (TPES) and ion dissociation breakdown curves for trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAN) were measured by imaging photoelectron photoion coincidence spectroscopy employing both effusive room-temperature samples and samples introduced in a seeded molecular beam. The fine structure in the breakdown diagram of TFA mirroring the vibrational progression in the TPES suggests that direct ionization to the X̃+ state leads to parent ions with a lower "effective temperature" than nonresonant ionization in between the vibrational progression. Composite W1U, CBS-QB3, CBS-APNO, G3, and G4 calculations yielded an average ionization energy (IE) of 11.69 ± 0.06 eV, consistent with the experimental value of 11.64 ± 0.01 eV, based on Franck-Condon modeling of the TPES. The measured 0 K appearance energies (AE0K) for the reaction forming CO2H+ + CF3 from TFA were 11.92 for effusive data and 11.94 ± 0.01 eV for molecular beam data, consistent with the calculated composite method 0 K reaction energy of 11.95 ± 0.08 eV. Together with the 0 K heats of formation (ΔfH0K) of CO2H+ and CF3, this yields a ΔfH0K of neutral TFA of -1016.6 ± 1.5 kJ mol-1 (-1028.3 ± 1.5 kJ mol-1 at 298 K). TFAN did not exhibit a molecular ion at room-temperature conditions, but a small signal was observed when rovibrationally cold species were probed in a molecular beam. The two observed dissociation channels were CF3C(O)OC(O)+ + CF3 and the dominant, sequential reaction CF3CO+ + CF3 + CO2. Calculations revealed a low-energy isomer of ionized TFAN, incorporating the three moieties CF3CO+, CF3, and CO2 joined in a noncovalent complex, mediating its unimolecular dissociation.

Dissociative photoionization of chromium hexacarbonyl: A round-trip ticket to non-statisticality and a detective story in thermochemistry

The fragmentation processes of internal energy selected chromium hexacarbonyl cations, Cr(CO)6+, were investigated by imaging photoelectron photoion coincidence (iPEPICO) spectroscopy at the VUV beamline of the Swiss Light Source. In the 9.3–21.5 eV photon energy range, Cr(CO)6+ dissociates by six sequential carbonyl ligand losses. The fragment ion fractional abundances, plotted in the breakdown diagram, along with the time-of-flight mass spectra for the first three metastable CO-loss channels were modeled using a statistical approach. Between 12 and 16 eV, the statistical model overestimates the degree of fragmentation, which is explained by enhanced kinetic energy release in impulsive CO loss on repulsive electronic states of the parent ion Cr(CO)6+, as confirmed by TD-DFT calculations. This is the first reported example for an embedded non-statistical unimolecular dissociation regime, bracketed by statistical regimes at low and at high energies. The statistical model was employed to derive 0 K appearance energies for Cr(CO)n+ (n = 0–5). The Cr(CO)5+ appearance energy and the literature COCr(CO)5+ bond dissociation energy yield an adiabatic Cr(CO)6+ ionization energy of 8.195 ± 0.120 eV, independent of photoelectron spectroscopy measurements. The 0 K appearance energy of Cr+ is 61 kJ mol–1 higher than predicted based on literature enthalpies of formation, which we suggest is most likely due to an error in the enthalpy of formation of Cr(CO)6, and propose a revised ΔfH[Cr(CO)6, g] = –972.1 ± 4.1 and –968.9 ± 4.1 kJ mol–1 at 0 and 298 K, respectively, and ΔfH298K[Cr(CO)6, c] = –1040.6 ± 4.2 kJ mol–1 for the crystalline state, based on the known enthalpy of sublimation. The measured CrCO bond dissociation energies in [(CO)nCrCO]+ (n = 0–5), and the enthalpies of formation of the chromium carbonyl ion series are also reported.

Low-Energy Photoelectron Spectrum and Dissociative Photoionization of the Smallest Amides: Formamide and Acetamide.

The threshold photoelectron spectrum and low-energy dissociative photoionization processes of formamide and acetamide were studied using photoelectron photoion coincidence spectroscopy and vacuum ultraviolet synchrotron radiation. Ab initio calculations and Franck-Condon simulations helped us assign the main vibrational progressions in the spectra and enabled the first conclusive assignment of the first electronically excited states. The adiabatic ionization energies to the X̃+ and Ã+ states of formamide (10.236 ± 0.004 and 10.643 ± 0.015 eV) and acetamide (9.734 ± 0.008 and 10.282 ± 0.020 eV) have been re-evaluated and spectroscopic transitions were assigned using a Franck-Condon approach. The cationic potential energy surface was explored to rationalize the observed fragmentation patterns and to construct a statistical model, which was fitted to the experimental breakdown diagram. Thermochemical thresholds were measured and calculated for H, CO, and NH2 loss from HCONH2+ as well as for CH3, NH2, CO, HCCO, and NH3 loss from CH3CONH2+. We present the first comprehensive, experimental and theoretical treatise of these fragmentation processes. The statistical model confirms fast internal conversion between the X̃+ and Ã+ states in formamide, as H transfer in CO loss is shown to take place on the excited state surface. It also explains the five almost simultaneously opening dissociation channels in the acetamide cation quantitatively. The derived 0 K appearance energies have been confirmed by ab initio calculations and by comparison with state-of-the-art thermochemical data, and some of the previous results have been revised by more than 10 times their stated uncertainty.

Dissociations of water ions after valence and inner-valence ionization

Energy selected and mass-resolved electron-ion coincidence spectra of heavy water have been recorded for ionization energies from 18 to 35 eV. Dissociation from the B2B2 state produces both O+ and D2 + at energies near their thermodynamic thresholds in addition to the known products D+ and OD+. The relative yields of O+, OD+, and D+ in the B2B2 state breakdown diagram are modulated by the vibrational structure of the B-state population, implying incomplete energy equilibration before fragmentation. Decay from the C-state produces OD+ in addition to the known O+ and D+. The fragment kinetic energies suggest that O+ and D+ from the C state are the products of full atomization of the molecule.

Radical Thermometers, Thermochemistry, and Photoelectron Spectra: A Photoelectron Photoion Coincidence Spectroscopy Study of the Methyl Peroxy Radical.

We investigated the simplest alkylperoxy radical, CH3OO, formed by reacting photolytically generated CH3 radicals with O2, using the new combustion reactions followed by photoelectron photoion coincidence (CRF-PEPICO) apparatus at the Swiss Light Source. Modeling the experimental photoion mass-selected threshold photoelectron spectrum using Franck-Condon simulations including transitions to triplet and singlet cationic states yielded the adiabatic ionization energy of 10.265 ± 0.025 eV. Dissociative photoionization of CH3OO generates the CH3+ fragment ion at the appearance energy of 11.164 ± 0.010 eV. Combining these two values with ΔfH0K°(CH3) yields ΔfH0K°(CH3OO) = 22.06 ± 0.97 kJ mol-1, reducing the uncertainty of the previously determined value by a factor of 5. Statistical simulation of the CH3OO breakdown diagram provides a molecular thermometer of the free radical's internal temperature, which we measured to be 330 ± 30 K.