Quantum mechanics: cleaning up metaphysical baggage

The dynamic electronic structure of atoms and molecules can be directly observed by means of the (e, 2e) reaction, which measures the distribution of energies and momenta of two electrons in coincidence after a knockout reaction initiated by an electron beam of known momentum incident on a molecular gas target. The molecular state for each event is identified by the electron separation energy. The recoil momentum for each event is known from the difference of measured initial and final momenta. It has been verified that values of this momentum are equal under suitable conditions to the momentum of the electron in the target immediately before knockout. Thus the spherically-averaged electron momentum distribution for each molecular orbital is measured. This is directly related to molecular orbitals calculated by the methods of quantum chemistry. Properties obtained by this method for different types of molecules are discussed.     

Gas phase high temperature photoelectron spectroscopy: an investigation of the transition metals scandium and vanadium

The He(I) photoelectron spectra of atomic scandium and vanadium have been recorded in the gas-phase. For scandium two bands associated with a (4s)^?1 ionization and one band associated with a (3d)^?1 ionization of the neutral atom have been observed. Measurement of their relative intensities allows the σ_3d:σ_4s photoionization cross-section ratio in atomic scandium to be estimated as 57.1 ± 9.0. In the atomic vanadium spectrum, six bands were seen. Four of these correspond to (3d)^?1 and (4s)^?1 ionizations of the ground state of the neutral atom, the V a⁴F state, whereas two bands correspond to (3d)^?1 ionizations of an excited state, the V a₆D state, which is approximately 2100 cm^?1 above the ground state. Measurement of the intensities of bands arising from the V a₄F state allows σ_3d:σ_4s to be estimated as 29.8 ± 2.5 for vanadium. Spectra of vanadium have been recorded with both single- and multi-detector photoelectron spectrometers. Comparison of the data acquisition rates obtained with both spectrometers demonstrates the advantage of using a multidetector instrument in high temperature photoelectron spectroscopy.     

Ionization energies of the diatomic halogens and interhalogens studied with relativistic hartree-fock-slater calculations

Vertical ionization energies from the outermost two π and two σ molecular orbitals in the diatomic halogen and interhalogen molecules have been calculated using a relativistic Hartree-Fock-Slater (HFS) method. The results obtained are in good agreement with the corresponding experimental ionization energies obtained from photoelectron spectroscopy. The spin-orbit splittings of the ²Π cationic states are rationalized in terms of the degree of localization of the partially filled π orbital in the cation on the header atom.     

Pavinane and isopavinane alkaloids: Correlation of absolute configurations by synthesis

(?)-Caryachine (9) and (?)-Reframoline (10) have been synthesised from a common intermediate; this confirms the absolute configuration in the isopavinane series deduced previously by application of the aromatic chirality rule. This also represents the first synthesis of an optically active pavinane alkaloid.     

Palladium assisted organic reactions-II: Ortho-aminomethylstilbene derivatives

Di-μ-chlorobis(N,N-dimethyl-3,4-dimethoxybenzylamine-6-C,N)dipalladium (1b) reacts readily with a variety of styrenes to give good yields of the corresponding o-aminomethylstilbene derivatives.     

The synthesis of berberastine

The structure of berberastine iodide (1a) has been confirmed by a synthesis of its racemate. The key intermediate is the 7,8-dimethoxy-3-arylisoquinoline derivative (3a) and several methods for its formation were studied.     

The He(I) photoelectron spectra of BrF and IF

The vacuum ultraviolet photoelectron spectra of BrF (X¹Σ⁺) and IF (X¹ Σ⁺) have been recorded and interpreted with the aid of both MS — Xα — SCF calculations and ab initio calculations. For both BrF and IF the first band is split by spin—orbit coupling into two components corresponding to ionization to the X²Π$\text{3}\text{2}$ Phytochemistry and X²Π$\text{1}\text{2}$ ionic states. Estimates of re, ?we and De for these states have been made.     

Observation and assignment of the first photoelectron band of the CH3CO (XA) radical

HeI photoelectron spectra have been recorded for the reaction of fluorine atoms with acetaldehyde at different reaction times. A structured band associated with a short-lived primary reaction product was recorded at a reactant mixing distance of 6 mm above the photon beam. The vertical ionization energy was measured as (8.39 ± 0.05 eV), and regularly spaced vibrational structure was observed in this band with an average vibrational separation of (1605 ± 30 cm⁻¹). The band was assigned to ionization of the CH₃CO (X²A) radical on the basis of first vertical ionization energies computed for the two possible primary products, CH₃CO and CH₂CHO, using ab-initio calculations. The calculations carried out on CH₃CO (X²A), and its singlet ground cationic state, revealed that the observed vibrational structure can be assigned to excitation of the CO stretching mode in the ion. The measured adiabatic ionization energy, 7.21 ± 0.05 eV, is higher than the value expected (6.94 ± 0.03 eV) from evidence in the literature and calculated values in this work. This difference is assigned to poor Franck–Condon factors in the region of the band onset which means that the true adiabatic ionization energy was not observed.     

An ab initio study of the low-lying electronic states of YO2 and Franck-Condon simulation of the first photodetachment band of YO2(-)

A variety of density functional theory and ab initio methods, including B3LYP, B98, BP86, CASSCF, CASSCF/RS2, CASSCF/MRCI, BD, BD(T), and CCSD(T), with ECP basis sets of up to the quintuple-zeta quality for Y, have been employed to study the X(2)B2 state of YO2 and the X(1)A1 state of YO2(-). Providing that the Y 4s(2)4p(6) outer-core electrons are included in the correlation treatment, the RCCSD(T) method gives the most consistent results and is concluded to be the most reliable and practical computational method for YO2 and YO2(-). In addition, RCCSD(T) potential energy functions (PEFs) of the X(2)B2 state of YO2 and the X(1)A1 state of YO2(-) were computed, employing the ECP28MDF_aug-cc-pwCVTZ and aug-cc-pVTZ basis sets for Y and O, respectively. Franck-Condon factors, which include allowance for Duschinsky rotation and anharmonicity, were calculated using the computed RCCSD(T) PEFs and were used to simulate the first photodetachment band of YO2(-). The simulated spectrum matches very well with the corresponding experimental 355 nm photodetachment spectrum of Wu, H.; Wang, L.-S. J. Phys. Chem. A 1998, 102, 9129, confirming the reliability of the RCCSD(T) PEFs used. Further calculations on low-lying electronic states of YO2 gave T(e)'s and T(vert)'s of the A(2)A1, B(2)B1, and C(2)A2 states of YO2, as well as EAs and VDEs to these states from the X(1)A1 state of YO2(-). On the basis of the ab initio VDEs obtained in the present study, previous assignments of the second and third photodetachment bands of YO2(-) have been revised.     

Ab initio calculations on SCl2 and low-lying cationic states of SCl2+: Franck-Condon simulation of the UV photoelectron spectrum of SCl2

Geometry optimization calculations were carried out on the (approximate)X (1)A(1) state of SCl(2) and the (approximate)X(2)B(1), (approximate)A(2)B(2), (approximate)B(2)A(1), (approximate)C(2)A(1), (approximate)D(2)A(2), and (approximate)E (2)B(2) states of SCl(2) (+) at the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] level with basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron correlation, basis set extension to the complete basis set limit, and relativistic contributions on computed minimum-energy geometrical parameters and/or relative electronic energies were also investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the (approximate)X (1)A(1) state of SCl(2) and the low-lying states of SCl(2)(+) listed above employing the aug-cc-pV(5+d)Z basis set. Anharmonic vibrational wave functions of these neutral and cationic states of SCl(2), and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T)aug-cc-pV(5+d)Z PEFs. Calculated FC factors with allowance for the Duschinsky rotation and anharmonicity were used to simulate the first four photoelectron (PE) bands of SCl(2). The agreement between simulated and observed He I PE spectra reported by Colton et al. [J. Electron Spectrosc. Relat. Phenom. 3, 345 (1974)] and Solouki et al. [Chem. Phys. Lett. 26, 20 (1974)] is excellent. However, our FC spectral simulations indicate that the first observed vibrational component in the first PE band of SCl(2) is a "hot" band arising from the SCl(2)(+)(approximate)X(2)B(1)(0,0,0)<--SCl(2)(approximate)X (1)A(1)(1,0,0) ionization. Consequently, the experimental adiabatic ionization energy of SCl(2) is revised to 9.55+/-0.01 eV, in excellent agreement with results obtained from state-of-the-art ab initio calculations in this work.