Potential energy surfaces of various primary and secondary products from the photodissociation of propyne and allene, including the C 3 H n (n ) 1-3) species, have been investigated at the CCSD(T)/6-311+G-(3df,2p)//B3LYP/6-311G(d,p) level of theory. The calculated heats of the reactions and the activation barriers for H 2 elimination from C 3 H n (n ) 2-4) have been employed to analyze the experimental translational energy distribution for different photodissociation channels. The electronic spectra of propyne and various isomers of C 3 H 2 have been calculated by using the CASSCF, MRCI, and EOM-CCSD methods with the ANO(2+) basis set. The calculations suggest that the photodissociation of propyne at 193 nm involves a Franck-Condon transition to the 1 E excited state. After internal conversion into the vibrationally excited ground electronic state, propyne can either dissociate to produce HCCCH + H 2 or isomerize to allene which, in turn, undergoes the H 2 elimination giving H 2 CCC. The HCCCH produced from propyne can have sufficiently high internal energy to rearrange to H 2 CCC. In both mechanisms, the formation of C 3 + H 2 from propyne and allene goes via the same intermediate, which explains the identical rotational distribution of the C 3 products in experiment. The H 2 elimination is a minor channel of propyne photodissociation and the major channel is elimination of the acetylenic hydrogen atom. The rearrangement mechanism of C 3 H 2 in the ground electronic state also has been studied. Automerization of H 2 CCC can take place either via a cyclopropyne transition state (the barrier is 37.5 kcal/mol, ref 18) or through isomerization to cyclopropenylidene and backward via TS6 (the barrier is 41.7 kcal/mol). Isomerization of triplet propargylene to cyclo-C 3 H 2 occurs by the ring closure via the triplet-singlet seam of crossing MSX1, and the activation energy is predicted to be about 41 kcal/mol. Cyclopropenylidene can undergo automerization by the 1,2-H shift via TS10 with the barrier of 32.4 kcal/mol. The direct triplet HCCCH f H 2 CCC isomerization proceeds by the 1,3-hydrogen shift via MSX2 and TS8 or TS9 with a high activation energy of 78-81 kcal/mol. The singlet propargylene can also rearrange to cyclo-C 3 H 2 via TS7 (barrier 37.4 kcal/mol) and to H 2 CCC via TS8 or TS9. The calculated PES for the ground and excited states have allowed us to explain the experimentally observed automerizations and isomerizations of C 3 H 2 isomers and to assign their UV absorption spectra.

Gold(I) carbene complexes of the type [Au(NHC)Cl], where NHC represents N-heterocyclic carbenes, have been synthesized. Two crystal structures of this type show that the molecules are stacked to form a linear polymer with Au‚‚‚Au interactions. Luminous [Au(NHC)(cbz)] (cbz ) carbazolate) were synthesized from [Au(NHC)Cl]. The crystal structure of one of this series indicates that the carbene and cbz rings are coplanar and two molecules are arranged pairwise in a head-to-tail fashion. While all the compounds prepared exhibit high-energy emission bands at ∼400 nm, [Au(NHC)Cl] complexes display additional low-energy emission bands at 580-650 nm, which are attributed to Au-centered transitions involving Au‚‚‚Au interactions. On the other hand, the low-energy emission bands of the [Au(NHC)(cbz)] complexes, which appear at 584-592 nm with fine structures, are likely to arise from the transitions involving mainly carbazolate tuned by Au, as also suggested by the density functional calculations. Crystal structures of Au(I)-dicarbenes are also reported.

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.