1,720,991 research outputs found
The potential energy and dipole moment surfaces of HOBr
No full textA theoretical study of the spectroscopy of HOBr and its deuterated isotopomer is presented. Highly accurate ab initio potential energy and dipole moment surfaces have been determined at the multireference configuration interaction level of theory, with large triple-ζ quality basis sets. From the analytic expression of the PES, a quartic anharmonic force field is derived, which, after a little empirical adjustment on the harmonic part, is used to evaluate spectroscopic parameters by means of standard perturbative formulae. Comparisons with experiment and previous computations are made
The gas-phase infrared spectra of anthracene-h10 and anthracene-d10
No full textThe IR spectra of anthracene-h10 and -d10 have been recorded for the first time in the gas phase from 450 to 3200 cm-1 with a resolution of 0.2 cm-1, using a multipass cell heated to 100°C. For the assignment of vibrational bands we have evaluated the theoretical spectrum using density functional theory (DFT) and scaled self consistent field force fields. We found that both methods reproduce the sequence of the experimental frequencies to a good accuracy, allowing in most cases consistent and unambiguous assignments. The relative intensities of C14H10 and C14D10 have also been measured and compared to theory. © 1997 American Institute of Physics
The gas-phase infrared spectra of phenanthrene-h10 and phenanthrene-d10
No full textThe IR spectra of phenanthrene-h10 and -d10 have been recorded in the vapour phase from 200 to 3200 cm-1 with a resolution of 0.2 cm-1, using a multipass cell heated at 90°C. The assignment of the vibrational bands has been performed by comparison with the theoretical spectra, evaluated using Density Functional Theory and Scaled Quantum Mechanical (SQM) force fields. We found that both methods reproduce the sequence of the experimental frequencies to a good accuracy, allowing in most cases consistent and unambiguous assignments. The relative intensities have also been measured and compared with theory. © 1997 Elsevier Science B.V
Ligand control in multihaptotropic o-indenyl rhenium systems. experimental and theoretical study
No full textThe synthesis of a novel class of alcohol- and ether-functionalized indenyl ligands, focusing on the haptotropic rearrangements of the hybrid O-indenyl rhenium species, is herein described, eta(1)-Ind(x)(Ome)Re(CO)(5) (12(x)) and eta(3)-Ind(x)(OMe)Re(CO)(4) (13(x), x = a, d)[Ind(a)(OMe) = C9H6CH2CH(Me)OMe, 1(a); Ind(d)(OMe) = C9H6CH(CH2)(3)CHOMe, 1d(a)] are examples of a and allylic intermediates in the Cp substitution. The tuning of stercoelcctronic effects of the functionalized alkyl chain or the coordinating solvent (MeCN, THF) allows the study of the relative stabilities of the intercepted solvento species eta(5)-Ind(h)(OMe) Re(CO)(2)(NCMe), 14(b), eta(5)-Ind(c)(OMe)Re(CO)(2)(THF), 15(c), or the chelate [eta(5):k(1)-O-Ind(b,c)(O)Re(CO)(2)], 16(b,c{)Ind(b)(OMe) = [C9H6CH2CH(Ph)OMe](-), 4(b); Ind(c)(OMe) = [C9H6CH(Ph)CH2OMe](-), 4(c)}. DFT calculations reported oil some of the Ind(o) systems have been compared with those of smaller (Cp-O) 5(a) or larger (Flu(a)(O)) 10(a) congeners, confirming the experimental findings. As peculiar examples of the underrepresented low-valent rhenium alkoxy species, the isolation of k(1)-O-Hlnd(x)(O)Re(CO)(5) [X = a,b] is also reported
Computational Overview of a Pd-Catalyzed Olefin Bis-alkoxycarbonylation Process
Full text linkA comprehensive density functional theory analysis is reported for the one-pot bis-alkoxycarbonylation reaction of olefins to form succinic acid esters by action of the catalyst (N-N)Pd(TFA)2 (N-N = bis(2,6-dimethylphenyl)-2,3-dimethyl-1,4-diazabutadiene, TFA- = CF3CO2-). The selective and efficient process involves alkene (H2C=CHR), CO, methanol, and p-benzoquinone (BQ) molecules as reactants. The catalytic mechanism, previously proposed on the basis of available experimental and literature data, is critically revised here. A plethora of optimized intermediates and transition states and their correlating energy profiles allow a step by step reconstruction of the entire cycle, highlighting key mechanistic aspects, such as the role of the R substituent in the olefin. One of its effects is determined by the presence of a 2e- donor group, which, depending on its power, may affect the catalysis up to its total inhibition. As another aspect, the key diester product forms through a reductive elimination step (Pd(II) → Pd(0) transformation) that excludes the previously proposed attainment of a Pd(II)-hydride complex. Finally, the paper illustrates the action of the sacrificial BQ oxidant in the restoration of the original Pd(II) catalyst, as found for other strictly related cases. The energy profile indicates that the rate-determining step occurs in the initial part of the reaction, given a +29.6 kcal mol-1 energy barrier, associated with a methoxo migration into an adjacent CO ligand. The result foreshadows a rather slow activation of the catalyst and a long duration of the cycle
Gas-phase infrared spectrum of indazole. Scaled quantum mechanical force field and complete spectrum assignment
No full textThe gas-phase IR spectrum of indazole has been recorded from 100 to 4000 cm-1, using a multipass cell heated to 120 °C, and completely assigned using theoretical predictions based on the scaled quantum mechanical (SQM) method. The single-crystal IR spectrum of this molecule, previously reported, has been compared with our data and partially reassigned. The harmonic force field of indazole, evaluated at the HF-SCF level using 6-31G** orbitals, is corrected by scaling the force field over a convenient set of internal coordinates. Scaling factors were determined by least-squares fitting of the theoretical to the experimental frequencies of two parent molecules, benzene and pyrazole and their perdeuteriated isotopomers. Our final prediction gives frequencies for indazole which, on average, differ from experiment by 24 cm-1. We confirm the validity of the SQM method as a practical tool for a complete analysis of vibrational spectra, even for molecules of this complexity
Order and mobility of the fluorescent probe 1,6-diphenylhexatriene in a polyester liquid crystal polymer
No full textGas-phase IR spectrum of 7-azaindole. Scaled quantum mechanical force field and complete spectrum assignment
No full textThe gas-phase IR spectrum of 7-azaindole has been recorded from 100 to 4000 cm-1, using a multipass cell heated to ca. 110°C, and completely assigned using theoretical predictions based on the scaled quantum mechanical (SQM) method. The harmonic force field of 7-azaindole, evaluated at the HF-SCF level using 6-31G** orbitals, is corrected by scaling the force field over a convenient set of internal coordinates. Scaling factors were determined by least-squares fitting of the theoretical to the experimental frequencies of the two parent molecules, pyridine and pyrrole, and their perdeuteriated isotopomers. Our final prediction gives frequencies for 7-azaindole which on average differ from experiment by 18 cm-1
Recommended from our members
Theoretical calculation of absorption intensities of C2H and C2D
No full textThe theory of dipole-allowed absorption intensities in triatomic molecules is presented for systems with three close-lying electronic states of doublet multiplicity. Its derivation is within the framework of a recently developed variational method [CARTER, S., HANDY, N. C., PUZZARINI, C., TARRONI, R., and PALMIERI, P., 2000, Molec. Phys., 98,1967]. The method has been applied to the calculation of the infrared absorption spectrum of the C2H radical and its deuterated isotopomer for energies up to 10000 cm(-1) above the ground state, using highly accurate ab initio diabatic potential energy and dipole moment surfaces. The calculated spectra agree very well with those recorded experimentally in a neon matrix [FORNEY, D., JACOX, M. E., and THOMPSON, W. E., 1995, J. molee. Spectrosc., 170, 178] and assignments in the high energy region of the IR spectra are proposed for the first time
- …
