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A new potential energy surface for forming glycine in the gas phase, starting from association of aminoacetonitrile (NH2CH2CN) with OH followed by subsequent hydrolysis, was determined using CBS‐QB3 calculation. The overall activation energy was 90 kJ mol−1 or 0 without or with catalytic H2O, respectively. Alanine or serine was formed from 2‐aminopropionitrile (CH3CH(NH2)CN) or 2‐amino‐3‐hydrxypropionitrile (HOCH2CH(NH2)CN) instead of aminoacetonitrile with the overall activation energies of 89 or 49 kJ mol−1, respectively. When an additional H2O was involved in each reaction as a catalyst, barrierless reaction pathways were obtained. These results suggest that it is possible for investigated reactions to occur in interstellar ices along the proposed pathways, taking kinetic aspects into account. [ABSTRACT FROM AUTHOR]

The potential energy surface for the formation of protonated uracil (UH+) from urea and HC3O+ was explored by performing quantum chemical complete basis set-QB3 calculations. A barrierless pathway was found for the formation of UH+, which was estimated to occur in the interstellar medium (ISM) much faster than the timescale of chemical revolution of typical dense interstellar clouds. Investigation of further reactions of UH+ formed through the obtained pathway led to the conclusion that uracil could be produced on icy grain surfaces but not in the gas phase of the ISM. [ABSTRACT FROM AUTHOR]

Mass-analyzed ion kinetic energy spectrometry can play a significant role in the investigation of production of C7H7+ from toluene molecular ion. The previous mechanistic model was found to be compatible with the present kinetic energy release distribution data.

The bromium loss of the propargyl bromide molecular ion was investigated through mass-analyzed ion kinetic energy spectrometry. The kinetic energy release distribution in the unimolecular dissociation was obtained and the potential energy surface for the mechanistic pathway was studied by quantum chemical computations on the B3LYP/6-311G** density functional theory level. Computation of the rate constants with statistical rate models indicated that the product C3H3+ ion has only the cyclopropenium structure and that the observed unimolecular reaction occurs via tunneling through an isomerization barrier for the H-atom transfer.

The dynamics of dissociation of n-propylbenzene molecular ion were investigated using mass-analyzed ion kinetic energy spectrometry. Specifically, the production of C(sub 7)H(sub 7)(super +) from the ion was examined and the kinetic energy release distributions in photodissociation and metastable ion decomposition were calculated. Experimental results revealed the C(sub 2)H(sub 5)(super *) loss of the n-propylbenzene molecular ion.

The mechanism of photodissociation of the bromobenzene molecular ion was investigated on a nanosecond time scale using photodissociation mass-analyzed ion kinetic energy spectrometry. In addition, the rate constant and kinetic energy release distribution were examined. Experimental results showed that the rate-energy data available over six orders of magnitude in time scale could be fit with a nontotally loose transition state model proposed by Rosenstock and colleagues. The model, however, predicts rate constant values larger than theoretically acceptable at high internal energy. An alternative model based on a completely loose transition state was suggested.

Syntheses of cytosine, uracil, and thymine starting from interstellar molecules were examined theoretically. Potential energy surfaces for the formation of protonated cytosine (CyH+), uracil (UrH+), and thymine (ThH+) from cyanoacetylene (HC3N), protonated isocyanic acid (H2NCO+), and one of NH3, H2O, and CH3OH, respectively, were determined by quantum chemical calculation using the CBS-QB3 method. Barrierless pathways were found for all the three reactions. Investigation of the energetics and kinetics of further possible reactions of CyH+, UrH+, and ThH+ led to the conclusion that cytosine, uracil, and thymine could not be formed along the proposed pathways in the interstellar gas phase, whereas their formation might be possible on interstellar icy grain mantles. [ABSTRACT FROM AUTHOR]

Previously developed technique of charge exchange ionization in a collision cell outside the ion source, which detects ions originating from the collision gas in the cell, was used to find long-lived excited electronic states of monosubstituted benzene cations. The technique is based on the criterion that charge exchange between polyatomic species is efficient only when the energy of reaction is close to zero or negative (ΔE≤0), or the exoergicity rule. The &Btilde; ²B[sub 2] states of chlorobenzene, bromobenzene, benzonitrile, and phenyl acetylene cations were found to have long lifetimes (10 microseconds or longer) while excited electronic states with long lifetime were not detected for fluorobenzene, iodobenzene, toluene, nitrobenzene, and styrene cations. The long-lived states found were those displaying well-resolved vibrational structures in the photoelectron spectra. In particular, these were the states generated by removal of an electron from the in-plane nonbonding p orbitals of halogens or in-plane π orbitals of the triple bonds. [ABSTRACT FROM AUTHOR]

of benzonitrile oxide to monosubstituted or 1,1-disubstituted alkenyl boronic ester gave only 2-isoxazolines, bearing the boronic ester group at the 5-position of the ring. On the other hand, the of benzonitrile oxide with trans-1,2-disubstituted alkenyl boronic esters produced 2-isoxazolines, bearing the boronic ester group at the 4-position of the ring. We used quantum mechanical calculations to investigate two regioisomeric channels that were associated with the formation of 2-isoxazolines, bearing the boronic ester group at the 4-position or 5-position. The study revealed that the experimental results agreed well with the parameters based on the transition state energies in gas or solvent phase. The study also informed that all the proceed in a spontaneous and exergonic fashion. [ABSTRACT FROM AUTHOR]

Carbon-rich radicals are important for understanding chemistry of flames as well as astrochemistry. However, they are elusive for both experiments and computations, due to the peculiarity of radicals. Here, we calculated excited states of the 1-buten-3-yn-2-yl ( HCCCCH2 , i- C4H3 ) and n- C4H3 ( HCCCHCH) radicals with the state-of-the-art complete active space self-consistent field ( CASSCF) and multi-reference configuration interaction ( MRCI) methods using the 6-311 + G(3df,2p) and aTVZ basis sets. The vertical energies for the seven excited states of each of the two isomers were obtained with the MRCI method at the geometries optimized at the CASSCF/6- 311G(d,p) level. The result using the aTVZ basis set has been more reliable than predicted with the 6-311 + G(3df,2p) basis set with the relative stability of the ground states of the two isomers better predicted in comparison to existing data. We believe that our results will be useful for understanding the chemistry of carbon-rich radicals. [ABSTRACT FROM AUTHOR]