Photodissociation of benzene under collision-free conditions: An ab initio/Rice-Ramsperger-Kassel-Marcus study

The ab initio/Rice-Ramsperger-Kassel-Marcus (RRKM) approach has been applied to investigate the photodissociation mechanism of benzene at various wavelengths upon absorption of one or two UV photons followed by internal conversion into the ground electronic state. Reaction pathways leading to various decomposition products have been mapped out at the G2M level and then the RRKM and microcanonical variational transition state theories have been applied to compute rate constants for individual reaction steps. Relative product yields (branching ratios) for C6H5+H, C6H4+H-2, C4H4+C2H2, C4H2+C2H4, C3H3+C3H3, C5H3+CH3, and C4H3+C2H3 have been calculated subsequently using both numerical integration of kinetic master equations and the steady-state approach. The results show that upon absorption of a 248 nm photon dissociation is too slow to be observable in molecular beam experiments. In photodissociation at 193 nm, the dominant dissociation channel is H atom elimination (99.6%) and the minor reaction channel is H-2 elimination, with the branching ratio of only 0.4%. The calculated lifetime of benzene at 193 nm is about 11 mus, in excellent agreement with the experimental value of 10 mus. At 157 nm, the H loss remains the dominant channel but its branching ratio decreases to 97.5%, while that for H-2 elimination increases to 2.1%. The other channels leading to C3H3+C3H3, C5H3+CH3, C4H4+C2H2, and C4H3+C2H3 play insignificant role but might be observed. For photodissociation upon absorption of two UV photons occurring through the neutral hot benzene mechanism excluding dissociative ionization, we predict that the C6H5+H channel should be less dominant, while the contribution of C6H4+H-2 and the C3H3+C3H3, CH3+C5H3, and C4H3+C2H3 radical channels should significantly increase. (C) 2004 American Institute of Physics

Femtosecond dynamics of hydrogen elimination: benzene formation from cyclohexadiene

Using femtosecond-resolved mass spectrometry in a molecular beam, we report real-time study of the hydrogen elimination reaction of 1,4-cyclohexadiene. The experimental observation of the ultrafast stepwise H-elimination elucidates the reaction dynamics and mechanism. With density-functional theory (ground-state) calculations, the nature of the reaction (multiple) pathways is examined. With the help of recent conical-intersection calculations, the excited-state and ground-state pathways are correlated. From these experimental and theoretical results we provide a unifying picture of the thermochemistry, photochemistry and the stereochemistry observed in the condensed phase

Effective equilibrium picture in xy−xy-model with exponentially correlated noise

We study the effect of exponentially correlated noise on $xy-$model in the limit of small correlation time discussing the order-disorder transition in mean-field and the topological transition in two dimensions. We map the steady states of the non-equilibrium dynamics into an effective equilibrium theory. In mean-field, the critical temperature increases with the noise correlation time $\tau$ indicating that memory effects promote ordering. This finding is confirmed by numerical simulations. The topological transition temperature in two dimensions remains untouched. However, finite size effects induce a crossover in the vortices proliferation that is confirmed by numerical simulations

STRUKTUR DAN DINAMIKA SOLVASI ION V2+ DALAM AIR BERDASARKAN SIMULASI DINAMIKA MOLEKUL MEKANIKA MOLEKUL

Penelitian ini dilakukan dengan tujuan untuk mempelajari struktur dan dinamika solvasi ion V2+ dalam air menggunakan simulasi dinamika molekul mekanika molekul. Subjek pada penelitian ini adalah hidrasi ion V2+ dan objek penelitian ini adalah struktur dan dinamika solvasi ion V2+ dalam air. Langkah awal yang dilakukan dalam penelitian ini adalah menentukan basis set yang terbaik. Kemudian menentukan potensial 2-badan dan 3-badan menggunakan simulasi dinamika molekul mekanika molekul yang akan menghasilkan file trajectory, lalu diolah lagi dan menghasilkan data berupa grafik RDF, CND, ADF dan dinamika ligan air. Berdasarkan analisis yang telah dilakukan bahwa struktur dari sistem hidrasi ion V2+ dengan simulasi DM MM2bd dan MM3bd adalah bipiramida pentagonal jumlah ligannya adalah 7. Sedangkan sifat dinamika dari sistem solvasi ion V2+ dengan molekul air menunjukkan bahwa pada simulasi MM2bd tidak terjadi perpindahan ligan air dan pada simulasi MM3bd terjadi perpindahan ligan air yang menandakan bahwa ligan air yang berikatan dengan ion V2+ tidak stabil

Ion spectroscopy in methane activation

Contains fulltext : 253677.pdf (Publisher’s version ) (Open Access)19 mei 202

Ruthenium and osmium clusters containing imido and sulfido ligands and their reactions with unsaturated organic molecules

Chapter 1 is an introduction to our research in triosmium and triruthenium clusters and details the different types of trinuclear clusters and capping ligands available. The uses of clusters in catalysis are then discussed. Chapter 2 describes the synthesis of amido and imido systems derived from [M3(CO)12] and NH2SO2tolyl. The formation and crystal structure of [Ru3(μ3-H)2(μ3-NSO2tolyl)(CO)9] is presented with its thermal decarbonylation to give [{Ru3(μ-H)2 (μ4-NSO2tolyl)(CO)7}2] (based on spectroscopic evidence) and protonation to give [Ru3(μ-H)3(μ3-NSO2tolyl)(CO)9]⁺. The deprotonation of [Os3(μ-H)(μ-NHSO2tolyl)(CO)10] to give the pyramidal μ2-imido system [OS3(μ-H)(μ-NSO2tolyl)(CO)10] which has been crystallographically characterised, is also discussed Chapter 3 reports the formation of the MeCN-substituted derivatives by treatment of [M3(μ-H)2(μ3-NSO2tolyl)(CO)9] with Me3NO.2H2O/MeCN. Important new discoveries on how alkynes are incorporated into these clusters are described, including single insertions into M-H bonds and coupling of alkenyl ligands formed by double insertions to give butadiene clusters. The crystal structures of [Os3(μ-trans-σ, η2-CH=CHBu)(μ3-NSO2tolyl)(CO)8] and [Ru3(μ-η2, η2-C4H6)(μ3-NSO2tolyl)(μ3- CO)(CO)7] are given. Chapter 4 studies the reactions of [M3(μ-H)2(μ3-S)(CO)8(MeCN)] (M = Ru or Os) with alkynes. Here evidence for the formation of double insertion products is presented as well as for single insertion products and butadiene clusters. The mode of coordination for the butadiene ligand in this case was different to those in Chapter 3. The crystal structure of [Os3(η4-PhCH=CHCPh=CH2)(μ3-S)(CO)8] is discussed. Studies on the reductive coupling of alkynes to give butadienes are described. Comparisons between the different effects of μ3-NSO2tolyl compared with μ3-S and Ru compared with Os are presented. Chapter 5 focuses on the coupling of high-valent with low-valent transition metal units within a single molecular cluster. For instance, the synthesis and characterisation of the high-low valent clusters [Ru3(CO)12MoX2] where MoX2 is the high-valent fragment is reported. The crystal structure of [Ru3(CO)12{Mo(N-2,6- Me2C6H3)2}] results on protonating this cluster are presented