In this paper we present calculated fractional abundances in dense interstellar clouds for selected atomic and molecular species using three different homogeneous, pseudo-time-dependent models discussed by Bettens, Lee, & Herbst (1995): the new standard model, neutral-neutral model 4. We have run each with 3 hydrogen densities – 103, 104, 105 cm-3 two temperatures 10 K 50 K. "Low metal" elemental been used all models; has also "high abundances.

A modified form of Shepard interpolation ab initio molecular potential energy surfaces is presented. This approach yields significant improvement in accuracy over previous related schemes. Here each Taylor expansion used the formula assigned a confidence volume which controls relative weight to that expansion. The parameters determining this are derived automatically from simple Bayesian analysis data. As iterative scheme expands data set, volumes also iteratively refined. for nine reactions...

A new fast scan submillimeter spectroscopic technique (FASSST) has been developed which uses a voltage tunable backward wave oscillator (BWO) as primary source of radiation, but (∼105 Doppler limited resolution elements/s) and optical calibration methods rather than the more traditional phase or frequency lock techniques. Among its attributes are (1) absolute to ∼1/10 gaseous absorption linewidth (<0.1 MHz, 0.000 003 cm−1), (2) high sensitivity, (3) ability measure many thousands...

A new chemical model of the circumstellar envelope surrounding carbon-rich star IRC+10216 is developed that includes carbon-containing molecules with up to 23 carbon atoms. The consists 3851 reactions involving 407 gas-phase species. Sizeable abundances a variety large — including clusters, unsaturated hydrocarbons and cyanopolyynes have been calculated. Negative molecular ions formulae CnH− (7≤n≤23) exist in considerable abundance, peak concentrations at distances from central somewhat...

In this study, we present a "black-box" method for fragmenting molecule with well-defined Kekulé or valence-bond structure into significant number of smaller fragment molecules that are more amenable to high level quantum chemical calculations. By taking an appropriate linear combination the energies, show it is possible in many cases obtain highly accurate total energies when compared energy full molecule. Our derived from approach reported by Deev and Collins, but contains unique elements,...

In this work we have demonstrated the free radical scavenging ability of two-hydroxy (catechol, hydroquinone, resorcinol) and three-hydroxy (phloroglucinol, pyrogallol, 1,2,4-benzenetriol) phenols against diphenylpicrylhydrazyl at various temperatures (15-40 degrees C) in different solvent media. Kinetic measurements, made by stopped-flow method, showed that with OH groups ortho positions largest rate coefficients compared to those meta para all Among ortho-structured catechol,...

ConspectusChemistry, particularly organic chemistry, is mostly concerned with functional groups: amines, amides, alcohols, ketones, and so forth. This because the reactivity of molecules can be categorized in terms reactions these groups, by influence other adjacent groups molecule. These simple truths ought to reflected electronic structure energy molecules, as determined structure. However, sophisticated ab initio quantum calculations molecular usually do not make apparent. In recent...

Here we present a new energy-based fragmentation method that is based on our previous work and combines the best elements of other methods. Our approach, termed "combined method", foremost simple to implement, robust, accurate, produces small fragments, which are independent conformation size target molecule. Essentially collections bonded atoms in molecule assigned groups. Fragment molecules formed by taking all pairs these These fragments then interacted with one another, interaction...

The first attempt to describe water dates back 1933 with the Bernal-Fowler model and it would take another forty years before computer simulation of liquid by Barker Watts in 1969. Since then, over a hundred different models have been proposed. Despite being widely studied, remains poorly understood. Examining evolution models, we identified three distinct philosophies modelling, namely employment effective point charges pioneering empirical incorporation polarization many-body inductive...

view Abstract Citations (101) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Importance of Classes Neutral-Neutral Reactions in the Production Complex Interstellar Molecules Bettens, R. P. A. ; Lee, H. -H. Herbst, Eric role classes neutral-neutral reactions gas-phase synthesis complex interstellar molecules is determined via a series model calculations. between O or N atoms and bare carbon clusters Cn appear to be critical hindering...

Recently, O−H bond dissociation enthalpies (BDEs) have been successfully used to express the free radical scavenging ability of polyphenolic antioxidants. In this work, BDEs phenol, catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, 1,2,4-benzenetriol, and 5-hydroxypyrogallol calculated at B3LYP/6-311G++(3df, 3pd) elucidate effect OH groups. Increasing number groups in adjacent (vicinal) position decreases BDE phenols. alternative C(1,3) as resorcinol C(1,3,5) phloroglucinol...

Longstanding conventional wisdom dictates that the widely used Many-Body Expansion (MBE) converges rapidly by four-body term when applied to large chemical systems. We have found, however, this is not true for calculations using many common, moderate-sized basis sets such as 6-311++G** and aug-cc-pVDZ. Energy performed on water clusters these showed a deceptively small error MBE was truncated at three-body level, while inclusion of four- five-body contributions drastically increased error....

The basis set superposition effect (BSSE) arises in electronic structure calculations of molecular clusters when questions relating to interactions between monomers within the larger cluster are asked. binding energy, or total may be broken down into many smaller subcluster and energies these subsystems linearly combined to, hopefully, produce desired quantity interest. Unfortunately, BSSE can plague fragment calculations. In this work, we carefully examine major sources error associated...

view Abstract Citations (49) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Abundance of Very Large Hydrocarbons and Carbon Clusters in the Diffuse Interstellar Medium Bettens, R. P. A. ; Herbst, Eric Two current gas-phase chemical models interstellar clouds have been extended to include hydrocarbons bare carbon clusters through 64 atoms size. new molecules comprise linear, monocyclic, tricyclic, fullerene/ane species but do not...

Current gas-phase models of dense cloud chemistry contain molecules through ≈ 10 atoms in size. We have extended two current reaction networks to include unsaturated hydrocarbons and bare carbon clusters up 64 The new consist linear, monocyclic, tricyclic, fullerene/ane species, but not polycyclic aromatic (PAHs). In an earlier paper, which was directed at a possible understanding the diffuse interstellar absorption band problem, we reported results for dispersive clouds, start as clouds...

Abstract The quartic centrifugal distortion constants of a class van der Waals complexes containing one or two rare gas atoms have been used to determine complete force field for the intermolecular vibrations. In such with Cs C2v symmetry atom is attached above plane are arranged symmetrically this plane. Small amplitude motions and an analytical form anharmonic interaction potential assumed analysis. Vibrational corrections applied planar moments inertia estimation pseudoequilibrium...

The nuclear magnetic shielding tensor is a molecular property that can be computed from first principles. In this work we show by utilizing the fragmentation approach, one able to accurately compute for large class of molecules. This great significance because computational expense required in evaluation all nuclei molecule now subject near linear scaling. On basis previous studies and work, it also very likely properties expressed as derivatives total energy system are amenable accurate via...

Many-body effects are required for an accurate description of both structure and dynamics large chemical systems. However, there numerous such interactions to consider, it is not obvious which ones significant. We provide a general fast method establishing small set three- four-body important. This achieved by estimating the maximum many-body effects, ϵmax, that can arise in given arrangement bodies. Through careful analysis we find two overall causes significant interactions. First,...

Interpolated ab initio potential energy surfaces which describe abstraction and exchange reactions in collisions of hydrogen water are reported. The electronic structure calculations performed at the QCISD(T) level theory, with an additivity approximation. A sufficiently large basis set is required to Rydberg character state for molecular configurations important process. Classical quantum dynamics on presented.

Abstract The quartic centrifugal distortion constants of a class van der Waals complexes containing one or two rare gas atoms have been used to determine complete force field for the intermolecular vibrations. In such with Cs C2v symmetry atom is attached above plane are arranged symmetrically this plane. Small amplitude motions and an analytical form anharmonic interaction potential assumed analysis. Vibrational corrections applied planar moments inertia estimation pseudoequilibrium...

The structure of the 1 : co-crystal formed between dicarboxylic acid, 2,2′-dithiodibenzoic and each isomeric 3- 4-pyridinealdazines features a supramolecular zig-zag chain constructed about O–Hacid⋯Npyridine synthon. By contrast, using same experimental conditions, only 2 3 could be when 2-pyridinealdazine was used. Here, pentamer is found, stabilised by synthon these associate to form via C–H⋯π contacts. Theory shows no significant differences in basicity pyridine-nitrogen atoms leading...

Structural investigations, i.e. solid-state (X-ray), solution (1H NMR) and gas-phase (theoretical), on molecules with the general formula MeOC(S)N(H)C6H4-4-Y: Y = H (1), NO2 (2), C(O)Me (3), Cl (4) have shown a preference for adoption of an E-conformation about central C–N bond. Such conformation allows formation dimeric hydrogen-bonded {⋯H–N–CS}2 synthon as building block. In cases 1–3, additional C–H⋯O interactions give rise to tapes varying topology. A theoretical analysis shows that is...

In this work, we show that our energy based fragmentation method (Bettens, R. P. A.; Lee, A. M. J. Phys. Chem. A 2006, 110, 8777) accurately reproduces the electrostatic potential for a selection of peptides, both charged and uncharged, other molecules biological interest at solvent accessible surface beyond when compared with full ab initio or density functional theory potential. We also consider ability various point charge models to reproduce compare results potentials latter being...