The potential energy surfaces for the chemical reactions of group 13 carbenoids have been studied using density functional theory (B3LYP/LANL2DZ). Five six-membered group 13 carbenoid species, HC(CMeNPh)2X, where X = B, Al, Ga, In, and Tl, have been chosen as model reactants in this work. Also, three kinds of chemical reaction, C−H bond insertion, alkene cycloaddition, and dimerization, have been used to study the chemical reactivities of these group 13 carbenoids. The present theoretical investigations suggest that the relative carbenoidic reactivity decreases in the order B > Al ≫ Ga > In > Tl. That is, the heavier the group 13 atom (X), the more stable is its carbenoid toward chemical reactions. This may be the reason that so far no experimental evidence for the HC(CMeNPh)2B species has been reported, while the other group 13 carbenoids are isolable at room temperature, since they are quite inert to chemical reaction. Furthermore, the group 13 carbenoid singlet−triplet energy splitting, as described in the configuration mixing model attributed to the work of Pross and Shaik, can be used as a diagnostic tool to predict their reactivities. The results obtained allow a number of predictions to be made.

The interstellar reaction of ground-state carbon atom with the simplest polyyne, diacetylene (HCCCCH), is investigated theoretically to explore probable routes to form hydrogen-deficient carbon clusters at ultralow temperature in cold molecular clouds. The isomerization and dissociation channels for each of the three collision complexes are characterized by utilizing the unrestricted B3LYP/6-311G(d,p) level of theory and the CCSD(T)/cc-pVTZ calculations. With facilitation of RRKM and variational RRKM rate constants at collision energies of 0-10 kcalmol, the most probable paths, thus reaction mechanism, are determined. Subsequently, the corresponding rate equations are solved that the evolutions of concentrations of collision complexes, intermediates, and products versus time are obtained. As a result, the final products and yields are identified. This study predicts that three collision complexes, c1, c2, and c3, would produce a single final product, 2,4-pentadiynylidyne, HCCCCC(X (2)Pi), C(5)H (p1)+H, via the most stable intermediate, carbon chain HC(5)H (i4). Our investigation indicates the title reaction is efficient to form astronomically observed 2,4-pentadiynylidyne in cold molecular clouds, where a typical translational temperature is 10 K, via a single bimolecular gas phase reaction.

The reaction between ground state carbon atoms, C(3P(j)), and phosphine, PH3(X(1)A1), was investigated at two collision energies of 21.1 and 42.5 kJ mol(-1) using the crossed molecular beam technique. The chemical dynamics extracted from the time-of-flight spectra and laboratory angular distributions combined with ab initio calculations propose that the reaction proceeds on the triplet surface via an addition of atomic carbon to the phosphorus atom. This leads to a triplet CPH3 complex. A successive hydrogen shift forms an HCPH2 intermediate. The latter was found to decompose through atomic hydrogen emission leading to the cis/trans-HCPH(X(2)A') reaction products. The identification of cis/trans-HCPH(X(2)A') molecules under single collision conditions presents a potential pathway to form the very first carbon-phosphorus bond in extraterrestrial environments like molecular clouds and circumstellar envelopes, and even in the postplume chemistry of the collision of comet Shoemaker-Levy 9 with Jupiter.

The reaction of ground-state carbon atom with a polyyne, triacetylene (HC6H) is investigated theoretically by combining ab initio calculations for predicting reaction paths, RRKM theory to yield rate constant for each path, and a modified Langevin model for estimating capturing cross sections. The isomerization and dissociation channels for each of the five collision complexes are characterized by utilizing the unrestricted B3LYP/6-311G(d,p) level of theory and the CCSD(T)/cc-pVTZ calculations. Navigating with the aid of RRKM rate constants through web of ab initio paths composed of 5 collision complexes, 108 intermediates, and 20 H-dissociated products, the most probable paths, reduced to around ten species at collision energies of 0 and 10 kcal/mol, respectively, are identified and adopted as the reaction mechanisms. The rate equations for the reaction mechanisms are solved numerically such that the evolutions of concentrations with time for all species involved are obtained and their lifetimes deduced. This study predicts that the five collision complexes, c1–c5, would produce a single final product, C7H (p1)+H, via the most stable intermediate, carbon chain HC7H (i1); namely, C+HC6H→HC7H→C7H+H. Our investigation indicates that the title reaction is efficient to form astronomically observed C7H in cold molecular clouds, where a typical translational temperature is 10 K.