Musculoskeletal simulation of professional ski jumpers during take-off considering aerodynamic forces.

Introduction: Musculoskeletal simulation has been widely used to analyze athletes' movements in various competitive sports, but never in ski jumping. Aerodynamic forces during ski jumping take-off have been difficult to account for in dynamic simulation. The purpose of this study was to establish an efficient approach of musculoskeletal simulation of ski jumping take-off considering aerodynamic forces and to analyze the muscle function and activity. Methods: Camera-based marker-less motion capture was implemented to measure the take-off kinematics of eight professional jumpers. A suitable full-body musculoskeletal model was constructed for the simulation. A method based on inverse dynamics iteration was developed and validated to estimate the take-off ground reaction force. The aerodynamic forces, which were calculated based on body kinematics and computational fluid dynamics simulations, were exerted on the musculoskeletal model as external forces. The activation and joint torque contributions of lower extremity muscles were calculated through static optimization. Results: The estimated take-off ground reaction forces show similar trend with the results from past studies. Although overall inconsistencies between simulated muscle activation and EMG from previous studies were observed, it is worth noting that the activation of the tibialis anterior, gluteus maximus, and long head of the biceps femoris was similar to specific EMG results. Among lower extremity extensors, soleus, vastus lateralis, biceps femoris long head, gluteus maximus, and semimembranosus showed high levels of activation and joint extension torque contribution. Discussion: Results of this study advanced the understanding of muscle action during ski jumping take-off. The simulation approach we developed may help guide the physical training of jumpers for improved take-off performance and can also be extended to other phases of ski jumping.

Effects of Tai Chi on Postural Control in People with Peripheral Neuropathy: A Systematic Review with Meta-Analysis.

BACKGROUND: Effects of Tai Chi on people with peripheral neuropathy (PN) are not yet apparent. This systematic review was conducted to evaluate the effects of Tai Chi on postural control in people with PN. METHODS: Literature was screened in seven databases for relevant randomized controlled trials. The reports and methodological quality were evaluated. A meta-analysis was performed using RevMan5.4 software. RESULTS: Ten reports were included, involving a total of 344 subjects. The meta-analysis found that Tai Chi therapy for people with PN resulted in a smaller sway area, in the double-leg stance with eyes closed test (SMD = -2.43, I2 = 0%), than that observed in the control group, greater distance covered in the six-minute walking test (SMD = -0.46, I2 = 49%) and faster performance in the timed-up-and-go test (SMD = 0.68, I2 = 50%), than the baseline. CONCLUSIONS: Tai chi effectively enhanced dynamic postural control in people with PN. However, no better effects on postural control from Tai Chi than from other rehabilitation approaches were observed in this study. Further high-quality trials are needed to better understand Tai Chi's effects on individuals with PN.

The Reduced Adaptability of H-Reflex Parameters to Postural Change With Deficiency of Foot Plantar Sensitivity.

Purpose: The project was to examine the influence of peripheral neuropathy (PN) severity on the relationship between Hoffmann-reflex (H-reflex) and postures. Methods: A total of 34 participants were recruited. H-reflex (H/M ratio and H-index) during prone, standing, and the heel-contact phase of walking was tested, along with foot sole sensitivity. Results: The participants were divided into three groups based on the severity of the foot sole sensitivity deficit: control, less (LA), and more (MA) affected with both feet 5.07 monofilament test scores ranging 10, 0-5, and 6-9, respectively. A significant group by the posture interaction was observed in the H/M ratio (F3.0, 41.9 = 2.904, p = 0.046, η p 2 = 0.172). In the control group, the H/M ratio of prone (22 ± 7%) was greater than that of the standing (13 ± 3%, p = 0.013) and heel-contact phase (10 ± 2%, p = 0.004). In the MA group, the H/M ratio of standing (13 ± 3%) was greater than that of the heel-contact phase (8 ± 2%, p = 0.011). The H-index was significantly different among groups (F2,28 = 5.711, p = 0.008, and η p 2 = 0.290). Post hoc analysis showed that the H-index of the control group (80.6 ± 11.3) was greater than that of the LA (69.8 ± 12.1, p = 0.021) and MA groups (62.0 ± 10.6, p = 0.003). Conclusion: In a non-PN population, the plantar sensory input plays an important role in maintaining standing postural control, while as for the PN population with foot sole sensitivity deficiency, type Ⅰ afferent fibers reflex loop (H-reflex) contributes more to the standing postural control. The H-index parameter is an excellent method to recognize the people with and without PN but not to distinguish the severity of PN with impaired foot sole sensitivity.

The effect of loss of foot sole sensitivity on H-reflex of triceps surae muscles and functional gait.

Objective: To investigate the effects of foot sole insensitivity on the outcomes of the triceps surae muscle H-reflex and functional gait. Material and Methods: People with peripheral neuropathy were recruited and divided into two groups: people with more (n = 13, 73.3 ± 4.3 years old) or less (n = 10, 73.5 ± 5.3) sensitive tactile sensation. Their monofilament testing scores were 9.0 ± 1.5 (range: 7-10) and 2.3 ± 2.4 (range: 0-6) out of 10, respectively. H-reflex of the triceps surae muscles during quiet standing and their relationship with functional gait, 6 min walking distance (6MWD), and timed-up-and-go duration (TUG), were compared between groups. Results: No significant difference was detected for H-reflex parameters between the groups. The less sensitive group showed reduced (p < .05) functional gait capacity compared to the other group, 38.4 ± 52.7 vs. 463.5 ± 47.6 m for 6MWD, and 9.0 ± 1.5 vs. 7.2 ± 1.1s for TUG, respectively. A significant correlation (p < .05), worse functional gait related to greater H/M ratio, was observed in the less sensitive group, not the other group. Conclusion: Although there was no significant H-reflex difference between the groups, more pronounced tactile sensation degeneration affected functional gaits and their relationship with H-reflex.

The Impact of Hoffmann Reflex on Standing Postural Control Complexity in the Elderly with Impaired Plantar Sensation.

In people with peripheral neuropathy (PN), impaired plantar sensation can cause adaptive changes in the central nervous system (CNS), resulting in changes in the standing postural control, which is reflected in the variability of standing output signals. Standard deviation (SD) and entropy are reliable indicators of system variability, especially since entropy is highly sensitive to diseased populations. The relation between SD and entropy, CNS and center of pressure (COP) variability is unclear for people with severe PN. The purpose of this study was to explore the adaptability of the CNS to the severe of PN and its effect on the degree and complexity of COP variability. Here, people with PN were divided into less affected (LA) and more affected (MA) groups based on plantar pressure sensitivity. We studied Hoffmann reflex (H-reflex) and standing balance performance with the control group (n = 8), LA group (n = 10), and MA group (n = 9), recording a 30 s COP time series (30,000 samples) of double-leg standing with eyes open. We observed that the more affected group had less COP complexity than people without PN. There is a significant negative correlation between the SD and sample entropy in people without PN, less affected and more affected. The COP complexity in people without PN was inversely correlated with H-reflex. We concluded that: (1) The complexity of COP variability in patients with severe plantar sensory impairment is changed, which will not affect the degree of COP variability; (2) The independence of the COP entropy in the AP and ML directions decreased, and the interdependence increased in people with PN; (3) Although the CNS of people with PN has a greater contribution to standing balance, its modulation of standing postural control is decreased.

Highly Charged Protein Ions: The Strongest Organic Acids to Date.

The basicity of highly protonated cytochrome c (cyt c) and myoglobin (myo) ions were investigated using tandem mass spectrometry, ion-molecule reactions (IMRs), and theoretical calculations as a function of charge state. Surprisingly, highly charged protein ions (HCPI) can readily protonate non-polar molecules and inert gases, including Ar, O2 , and N2 in thermal IMRs. The most HCPIs that can be observed are over 130 kJ mol-1 less basic than the least basic neutral organic molecules known (tetrafluoromethane and methane). Based on theoretical calculations, it is predicted that protonated cyt c and myo ions should spontaneously lose a proton to vacuum for charge states in which every third residue is protonated. In this study, HCPIs are formed where every fourth residue on average is protonated. These results indicate that protein ions in higher charge states can be formed using a low-pressure ion source to reduce proton-transfer reactions between protein ions and gases from the atmosphere.

A crossed beam and ab initio investigation on the formation of vinyl boron monoxide (C2H3BO; X1A') via reaction of boron monoxide (11BO; X2Σ+) with ethylene (C2H4; X1A(g)).

The reaction dynamics of the boron monoxide radical ((11)BO; X(2)Σ(+)) with ethylene (C(2)H(4); X(1)A(g)) were investigated at a nominal collision energy of 12.2 kJ mol(-1) employing the crossed molecular beam technique and supported by ab initio and statistical (RRKM) calculations. The reaction is governed by indirect scattering dynamics with the boron monoxide radical attacking the carbon-carbon double bond of the ethylene molecule without entrance barrier with the boron atom. This addition leads to a doublet radical intermediate (O(11)BH(2)CCH(2)), which either undergoes unimolecular decomposition through hydrogen atom emission from the C1 atom via a tight transition state located about 13 kJ mol(-1) above the separated products or isomerizes via a hydrogen shift to the O(11)BHCCH(3) radical, which also can lose a hydrogen atom from the C1 atom. Both processes lead eventually to the formation of the vinyl boron monoxide molecule (C(2)H(3)BO; X(1)A'). The overall reaction was determined to be exoergic by about 40 kJ mol(-1). The reaction dynamics are also compared to the isoelectronic ethylene (C(2)H(4); X(1)A(g)) - cyano radical (CN; X(2)Σ(+)) system studied earlier.

A VUV photoionization study of the combustion-relevant reaction of the phenyl radical (C6H5) with propylene (C3H6) in a high temperature chemical reactor.

We studied the reaction of phenyl radicals (C(6)H(5)) with propylene (C(3)H(6)) exploiting a high temperature chemical reactor under combustion-like conditions (300 Torr, 1200-1500 K). The reaction products were probed in a supersonic beam by utilizing tunable vacuum ultraviolet (VUV) radiation from the Advanced Light Source and recording the photoionization efficiency (PIE) curves at mass-to-charge ratios of m/z = 118 (C(9)H(10)(+)) and m/z = 104 (C(8)H(8)(+)). Our results suggest that the methyl and atomic hydrogen losses are the two major reaction pathways with branching ratios of 86 ± 10% and 14 ± 10%. The isomer distributions were probed by fitting the recorded PIE curves with a linear combination of the PIE curves of the individual C(9)H(10) and C(8)H(8) isomers. Styrene (C(6)H(5)C(2)H(3)) was found to be the exclusive product contributing to m/z = 104 (C(8)H(8)(+)), whereas 3-phenylpropene, cis-1-phenylpropene, and 2-phenylpropene with branching ratios of 96 ± 4%, 3 ± 3%, and 1 ± 1% could account for the signal at m/z = 118 (C(9)H(10)(+)). Although searched for carefully, no evidence of the bicyclic indane molecule could be provided. The reaction mechanisms and branching ratios are explained in terms of electronic structure calculations nicely agreeing with a recent crossed molecular beam study on this system.

Chemical dynamics of the CH(X2Π) + C2H4(X1A1g), CH(X2Π) + C2D4(X1A1g), and CD(X2Π) + C2H4(X1A1g) reactions studied under single collision conditions.

The crossed beam reactions of the methylidyne radical with ethylene (CH(X(2)Π) + C(2)H(4)(X(1)A(1g))), methylidyne with D4-ethylene (CH(X(2)Π) + C(2)D(4)(X(1)A(1g))), and D1-methylidyne with ethylene (CD(X(2)Π) + C(2)H(4)(X(1)A(1g))) were conducted at nominal collision energies of 17-18 kJ mol(-1) to untangle the chemical dynamics involved in the formation of distinct C(3)H(4) isomers methylacetylene (CH(3)CCH), allene (H(2)CCCH(2)), and cyclopropene (c-C(3)H(4)) via C(3)H(5) intermediates. By tracing the atomic hydrogen and deuterium loss pathways, our experimental data suggest indirect scattering dynamics and an initial addition of the (D1)-methylidyne radical to the carbon-carbon double bond of the (D4)-ethylene reactant forming a cyclopropyl radical intermediate (c-C(3)H(5)/c-C(3)D(4)H/c-C(3)H(4)D). The latter was found to ring-open to the allyl radical (H(2)CCHCH(2)/D(2)CCHCD(2)/H(2)CCDCH(2)). This intermediate was found to be long lived with life times of at least five times its rotational period and decomposed via atomic hydrogen/deuterium loss from the central carbon atom (C2) to form allene via a rather loose exit transition state in an overall strongly exoergic reaction. Based on the experiments with partially deuterated reactants, no compelling evidence could be provided to support the formation of the cyclopropene and methylacetylene isomers under single collision conditions. Likewise, hydrogen/deuterium shifts in the allyl radical intermediates or an initial insertion of the (D1)-methylidyne radical into the carbon-hydrogen/deuterium bond of the (D4)-ethylene reactant were found to be-if at all-of minor importance. Our experiments propose that in hydrocarbon-rich atmospheres of planets and their moons such as Saturn's satellite Titan, the reaction of methylidyne radicals should lead predominantly to the hitherto elusive allene molecule in these reducing environments.

Crossed beam reactions of methylidyne [CH(X2Π)] with D2-acetylene [C2D2(X1Σg(+))] and of D1-methylidyne [CD(X2Π)] with acetylene [C2H2(X1Σg(+))].

The crossed molecular beam reactions of ground state methylidyne, CH(X(2)Π), with D2-acetylene, C(2)D(2)(X(1)Σ(g)(+)), and of D1-methylidyne, CD(X(2)Π), with acetylene, C(2)H(2)(X(1)Σ(g)(+)), were conducted under single collision conditions at a collision energy of 17 kJ mol(-1). Four competing reaction channels were identified in each system following atomic 'hydrogen' (H/D) and molecular 'hydrogen' (H(2)/D(2)/HD) losses. The reaction dynamics were found to be indirect via complex formation and were initiated by two barrierless-addition pathways of methylidyne/D1-methylidyne to one and to both carbon atoms of the D2-acetylene/acetylene reactant yielding HCCDCD/DCCHCH and c-C(3)D(2)H/c-C(3)H(2)D collision complexes, respectively. The latter decomposed via atomic hydrogen/deuterium ejection to form the thermodynamically most stable cyclopropenylidene species (c-C(3)H(2), c-C(3)D(2), c-C(3)DH). On the other hand, the HCCDCD/DCCHCH adducts underwent hydrogen/deuterium shifts to form the propargyl radicals (HDCCCD, D(2)CCCH; HDCCCH, H(2)CCCD) followed by molecular 'hydrogen' losses within the rotational plane of the decomposing complex yielding l-C(3)H/l-C(3)D. Quantitatively, our crossed beam studies suggest a dominating atomic compared to molecular 'hydrogen' loss with fractions of 81 ± 23% vs. 19 ± 10% for the CD/C(2)H(2) and 87 ± 30% vs. 13 ± 4% for the CH/C(2)D(2) systems. The role of these reactions in the formation of interstellar isomers of C(3)H(2) and C(3)H is also discussed.

Low temperature formation of naphthalene and its role in the synthesis of PAHs (polycyclic aromatic hydrocarbons) in the interstellar medium.

Polycyclic aromatic hydrocarbons (PAHs) are regarded as key molecules in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest prototype-naphthalene (C(10)H(8))-has remained an open question. Here, we show in a combined crossed beam and theoretical study that naphthalene can be formed in the gas phase via a barrierless and exoergic reaction between the phenyl radical (C(6)H(5)) and vinylacetylene (CH(2) = CH-C ≡ CH) involving a van-der-Waals complex and submerged barrier in the entrance channel. Our finding challenges conventional wisdom that PAH-formation only occurs at high temperatures such as in combustion systems and implies that low temperature chemistry can initiate the synthesis of the very first PAH in the interstellar medium. In cold molecular clouds, barrierless phenyl-type radical reactions could propagate the vinylacetylene-mediated formation of PAHs leading to more complex structures like phenanthrene and anthracene at temperatures down to 10 K.

Crossed beam study of the atom-radical reaction of ground state carbon atoms (C(3P)) with the vinyl radical (C2H3(X2A')).

The atom-radical reaction of ground state carbon atoms (C((3)P)) with the vinyl radical (C(2)H(3)(X(2)A')) was conducted under single collision conditions at a collision energy of 32.3 ± 2.9 kJ mol(-1). The reaction dynamics were found to involve a complex forming reaction mechanism, which is initiated by the barrier-less addition of atomic carbon to the carbon-carbon-double bond of the vinyl radical forming a cyclic C(3)H(3) radical intermediate. The latter has a lifetime of at least 1.5 times its rotational period and decomposes via a tight exit transition state located about 45 kJ mol(-1) above the separated products through atomic hydrogen loss to the cyclopropenylidene isomer (c-C(3)H(2)) as detected toward cold molecular clouds and in star forming regions.

Phenoxy radical (C6H5O) formation under single collision conditions from reaction of the phenyl radical (C6H5, X2A1) with molecular oxygen (O2, X3Σg(-)): the final chapter?

The combustion relevant elementary reaction of photolytically generated phenyl radicals (C(6)H(5), X(2)A(1)) with molecular oxygen to form the phenoxy radical (C(6)H(5)O) plus a ground state oxygen atom was investigated under single collision conditions at a collision energy of 21.2 ± 0.9 kJ mol(-1). The reaction was found to proceed indirectly via the involvement of a long-lived phenylperoxy radical (C(6)H(5)O(2)) intermediate that decomposed via a rather loose exit transition state. In comparison with crossed beams data obtained previously at elevated collision energies, we suggest that, as the collision energy rises from 21 to 107 kJ mol(-1), the lifetime of the C(6)H(5)O(2) reaction intermediate decreases, that is, a classical behavior within the osculating complex model.

An LIF characterization of supersonic BO (X2Σ+) and CN (X2Σ+) radical sources for crossed beam studies.

Various ablation sources generating supersonic boron monoxide (BO; X(2)Σ(+)) radical beams utilizing oxygen (O(2)), carbon dioxide (CO(2)), methanol (CH(3)OH), and water (H(2)O) as seeding gases were characterized in a crossed molecular beams setup by mass resolved time-of-flight spectroscopy and spectroscopically via laser induced fluorescence. Intensities of the sources as well as rovibrational energy distributions were analyzed. The molecular oxygen source was found to produce excessive amount of an unwanted BO(2) byproduct. Internal vibrational energy of boron monoxide generated in the water and methanol sources was too high to be considered for the study of dynamics of ground state radicals. The best combination of intensity, purity, and low internal energy was found in the carbon dioxide source to generate boron monoxide. We successfully tested the boron monoxide (BO; X(2)Σ(+)) radical beam source in crossed beams reactions with acetylene (C(2)H(2)) and ethylene (C(2)H(4)). The source was also compared with supersonic beams of the isoelectronic cyano (CN; X(2)Σ(+)) radical.

Indene formation under single-collision conditions from the reaction of phenyl radicals with allene and methylacetylene--a crossed molecular beam and ab initio study.

Polycyclic aromatic hydrocarbons (PAHs) are regarded as key intermediates in the molecular growth process that forms soot from incomplete fossil fuel combustion. Although heavily researched, the reaction mechanisms for PAH formation have only been investigated through bulk experiments; therefore, current models remain conjectural. We report the first observation of a directed synthesis of a PAH under single-collision conditions. By using a crossed-molecular-beam apparatus, phenyl radicals react with C(3)H(4) isomers, methylacetylene and allene, to form indene at collision energies of 45 kJ mol(-1). The reaction dynamics supported by theoretical calculations show that both isomers decay through the same collision complex, are indirect, have long lifetimes, and form indene in high yields. Through the use of deuterium-substituted reactants, we were able to identify the reaction pathway to indene.

A crossed beam and ab initio investigation of the reaction of boron monoxide ((11)BO; X(2)Σ+) with acetylene (C2H2; X(1)Σ(g)+).

The reaction dynamics of boron monoxide (BO; X(2)Σ(+)) with acetylene (C(2)H(2); X(1)Σ(g)(+)) were investigated under single collision conditions at a collision energy of 13 kJ mol(-1) employing the crossed molecular beam technique; electronic structure RRKM calculations were conducted to complement the experimental data. The reaction was found to have no entrance barrier and proceeded via indirect scattering dynamics initiated by an addition of the boron monoxide radical with its boron atom to the carbon-carbon triple bond forming the O(11)BHCCH intermediate. The latter decomposed via hydrogen atom emission to form the linear O(11)BCCH product through a tight exit transition state. The experimentally observed sideways scattering suggests that the hydrogen atom leaves perpendicularly to the rotational plane of the decomposing complex and almost parallel to the total angular momentum vector. RRKM calculations indicate that a minor micro channel could involve a hydrogen migration in the initial collision to form an O(11)BCCH(2) intermediate, which in turn can also emit atomic hydrogen. The overall reaction to form O(11)BCCH plus atomic hydrogen from the separated reactants was determined to be exoergic by 62 ± 8 kJ mol(-1). The reaction dynamics were also compared with the isoelectronic reaction of the cyano radical (CN; X(2)Σ(+)) with acetylene (C(2)H(2); X(1)Σ(g)(+)) studied earlier.

On the formation of resonantly stabilized C5H3 radicals--a crossed beam and ab initio study of the reaction of ground state carbon atoms with vinylacetylene.

The formation of polycyclic aromatic hydrocarbons in combustion environments is linked to resonance stabilized free radicals. Here, we investigated the reaction dynamics of ground state carbon atoms, C((3)P(j)), with vinylacetylene at two collision energies of 18.8 kJ mol(-1) and 26.4 kJ mol(-1) employing the crossed molecular beam technique leading to two resonantly stabilized free radicals. The reaction was found to be governed by indirect scattering dynamics and to proceed without an entrance barrier through a long-lived collision complex to reach the products, n- and i-C(5)H(3) isomers via tight exit transition states. The reaction pathway taken is dependent on whether the carbon atom attacks the π electron density of the double or triple bond, both routes have been compared to the reactions of atomic carbon with ethylene and acetylene. Electronic structure/statistical theory calculations determined the product branching ratio to be 2:3 between the n- and i-C(5)H(3) isomers.

Formation of benzene in the interstellar medium.

Polycyclic aromatic hydrocarbons and related species have been suggested to play a key role in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest building block--the aromatic benzene molecule--has remained elusive for decades. Here we demonstrate in crossed molecular beam experiments combined with electronic structure and statistical calculations that benzene (C(6)H(6)) can be synthesized via the barrierless, exoergic reaction of the ethynyl radical and 1,3-butadiene, C(2)H + H(2)CCHCHCH(2) → C(6)H(6) + H, under single collision conditions. This reaction portrays the simplest representative of a reaction class in which aromatic molecules with a benzene core can be formed from acyclic precursors via barrierless reactions of ethynyl radicals with substituted 1,3-butadiene molecules. Unique gas-grain astrochemical models imply that this low-temperature route controls the synthesis of the very first aromatic ring from acyclic precursors in cold molecular clouds, such as in the Taurus Molecular Cloud. Rapid, subsequent barrierless reactions of benzene with ethynyl radicals can lead to naphthalene-like structures thus effectively propagating the ethynyl-radical mediated formation of aromatic molecules in the interstellar medium.

A crossed molecular beam study on the reaction of methylidyne radicals [CH(X(2)Π)] with acetylene [C(2)H(2)(X(1)Σ(g)(+))]-competing C(3)H(2) + H and C(3)H + H(2) channels.

We carried out the crossed molecular beam reaction of ground state methylidyne radicals, CH(X(2)Π), with acetylene, C(2)H(2)(X(1)Σ(g)(+)), at a nominal collision energy of 16.8 kJ mol(-1). Under single collision conditions, we identified both the atomic and molecular hydrogen loss pathways forming C(3)H(2) and C(3)H isomers, respectively. A detailed analysis of the experimental data suggested the formation of c-C(3)H(2) (31.5 ± 5.0%), HCCCH/H(2)CCC (59.5 ± 5.0%), and l-HCCC (9.0 ± 2.0%). The reaction proceeded indirectly via complex formation and involved the unimolecular decomposition of long-lived propargyl radicals to form l-HCCC plus molecular hydrogen and HCCCH/H(2)CCC plus atomic hydrogen. The formation of c-C(3)H(2) was suggested to be produced via unimolecular decomposition of the cyclopropenyl radical, which in turn could be accessed via addition of the methylidyne radical to both carbon atoms of the acetylene molecule or after an initial addition to only one acetylenic carbon atom via ring closure. This investigation brings us closer to unraveling of the reaction of important combustion radicals-methylidyne-and the connected unimolecular decomposition of chemically activated propargyl radicals. This also links to the formation of C(3)H and C(3)H(2) in combustion flames and in the interstellar medium.

On the directed gas phase synthesis of the imidoborane molecule (HNBH)--an isoelectronic molecule of acetylene (HCCH).

The elementary reaction of ground state boron atoms, (B((2)P(j))), with ammonia (NH(3)(X(1)A(1))) was conducted under single collision conditions at a collision energy of 20.5 ± 0.4 kJ mol(-1) in a crossed molecular beams machine. Combined with electronic structure calculations, our experimental results suggested that the reaction was initiated by a barrier-less addition of the boron atom to the nonbonding electron pair of the nitrogen atom forming a weakly bound BNH(3) collision complex. This intermediate underwent a hydrogen shift to a doublet HBNH(2) radical that decomposed via atomic hydrogen loss to at least the imidoborane (HBNH(X(1)Σ(+)) molecule, an isoelectronic species of acetylene (HCCH(X(1)Σ(g)(+))). Our studies are also discussed in light of the isoelectronic C(2)H(3) potential energy surface accessed via the isoelectronic carbon-methyl system.