Calculated Auger emission spectrum of ammonia

Doubly ionized states of ammonia are calculated with Roothaan's symmetry-restricted open-shell SCF method. A GTO basis of double-ζ quality is used. Calculated energies compare well with previous calculations for the lowest doubly ionized states. Auger emission intensities are estimated using an analogy with the experimental Auger spectrum of neon.     

Calculated electronic transitions of the water ammonia complex

We have calculated vertical excitation energies and oscillator strengths of the low lying electronic transitions in H2O, NH3, and H2ONH3 using a hierarchy of coupled cluster response functions [coupled cluster singles (CCS), second order approximate coupled cluster singles and doubles (CC2), coupled cluster singles and doubles (CCSD), and third order approximate coupled cluster singles, doubles, and triples (CC3)] and correlation consistent basis functions (n-aug-cc-pVXZ, where n=s,d,t and X=D,T,Q). Our calculations indicate that significant changes in the absorption spectra of the photodissociative states of H2O and NH3 monomers occur upon complexation. In particular, we find that the electronic transitions originating from NH3 are blueshifted, whereas the electronic transitions originating from H2O are redshifted.     

New perspectives on iron-ligand vibrations of oxyheme complexes

We report our studies of the vibrational dynamics of iron for three imidazole-ligated oxyheme derivatives that mimic the active sites of histidine-ligated heme proteins complexed with dioxygen. The experimental vibrational data are obtained from nuclear resonance vibrational spectroscopy (NRVS) measurements conducted on both powder samples and oriented single crystals, and which includes several in-plane (ip) and out-of-plane (oop) measurements. Vibrational spectral assignments have been made through a combination of the oriented sample spectra and predictions based on density functional theory (DFT) calculations. The two Fe-O(2) modes that have been previously observed by resonance Raman spectroscopy in heme proteins are clearly shown to be very strongly mixed and are not simply either a bending or stretching mode. In addition, a third Fe-O(2) mode, not previously reported, has been identified. The long-sought Fe-Im stretch, not observed in resonance Raman spectra, has been identified and compared with the frequencies observed for the analogous CO and NO species. The studies also suggest that the in-plane iron motion is anisotropic and is controlled by the orientation of the Fe-O(2) group and not sensitive to the in-plane Fe-N(p) bonds and/or imidazole orientations.     

Calculated properties of the active site complex of oxidized rubredoxins

The active site of rubredoxins, the simplest class of iron-sulfur, electron-transfer proteins consists of a single Fe atom surrounded by a distorted tetrahedral array of four cysteine sulfur atoms. With the aid of a newly formulated computer program, we have calculated the electric field gradient at the Fe⁵⁷ nucleus, the resultant quadrupole splitting (ΔE _Q) and the isotropic and anisotropic parts of the hyperfine interaction between the Fe nuclear spin and the net electron spin in the sextet ground state for ten conformational variations of the active site complex. For each conformer we used an electron distribution obtained from an Iterated Extended Huckel Theory (IEHT) molecular orbital calculation. Comparison of calculated and experimental results of (ΔE _Q) obtained from Mossbauer resonance spectra indicated that a number of conformers have field gradient values in excellent agreement with experiment. Good agreement with experiment was also found for the calculated hyperfine coupling constant. In this interaction, the isotropic contribution is dominant while the anisotropic contribution is more symmetry dependent. Since a single average experimental value is observed, hyperfine interaction in this system is not a very sensitive probe of active site conformation.     

Calculated electronic spectra of model ferric cytochrome P450 complexes

Restricted open-shell ground state properties and electronic spectra of two closely related low-spin, ferric, 6-coordinate, model cytochrome P450 complexes, one with a methyl mercaptide and the other a mercaptan as the second axial ligands, have been calculated with a newly modified, semiempirical INDO-SCF-CI method. The sensitivity of the calculated spectra to protonation of the sixth axial ligand, and the ability of the method to predict characteristic spectral features for the complexes investigated, are determined. Assignment of transitions, including xy- and z-polarized transitions, are made and compared with experimental observations where available. In particular, the origin of the anomalous split Soret spectrum observed in low-spin ferric complexes with mercaptide but not a mercaptan is investigated. Finally, a two part hypothesis is presented which provides a general explanation for the origin of both the observed split Soret and the red-shifted normal Soret in various ferrous and ferric P450 complexes in terms of the ground state orbital characters and simple symmetry considerations.     

Calculated ro-vibrational spectrum of 7Li+3 and 7Li2 6Li+

Calculated ro-vibrational energy levels (J ⩽ 4) and transition intensities are presented for the two most abundant isotopomers of Li⁺₃. The calculations use the recent ab initio potential energy surface of Searles et al. (Spectrochim. Acta 43A, 699 (1987); 44A, 505 (1988); 44A, 985 (1988)). The rotational levels of the ground state and vibrational fundamentals are given in terms of parameterised Hamiltonians due to Watson retaining terms to fourth-order. The small splitting of the degenerate ν₂ mode in the mixed isotopomer leads to strong Coriolis coupling between the ν₂ and ν₃ in ⁷Li₂ ⁶Li⁺.     

Calculated optical and magnetic properties of hexafluorouranate (V) anion: UF- 6

Our ab initio all-electron Dirac-Fock and the corresponding nonrelativistic limit calculations performed at four U-F bond distances yield for octahedral UF(6) (-) the optimized U-F bond distance of 2.091 and 2.088 A, respectively. We have also performed Dirac scattered wave calculations at the optimized U-F bond distances using the first-order pertubational procedure to obtain the Zeeman and hyperfine magnetic tensors for the octahedral anion UF(6) (-). The calculated isotropic Zeeman tensor of Deltag=-2.87 is in fairly good agreement with the value of Deltag=-2.78+/-0.10 obtained in electron spin resonance experiments on the H(3)O(+)UF(6) (-) adduct and the unpaired electron-spin spends approximately 2.5% of its time on the fluorine 2p(3/2) spinors. The calculated relativistic transition energies of the near-IR and visible absorption bands are also in good agreement with the experimental results. The octahedral uranium hexafluoride anion has a simple crystal field f(1) configuration; however, relativistic four-component wave functions are necessary to interpret correctly the available magnetic data, while a relativistic treatment taking into account double group symmetrized basis functions should suffice for the interpretation of the optical data.     

Optical absorption spectrum of nickel antipyrine complex

The optical absorption spectrum of nickel antipyrine complex has been studied both at laboratory and liquid nitrogen temperatures. The spectrum is characteristic of Ni²⁺ in an octahedral crystal field. A good fit between theoretical and experimental band positions is obtained for the following crystal field parameters:Dq = 940 cm⁻¹,B = 795 cm⁻¹, C = 4.7B.     

The rotational spectrum of the cyclopentadienylallylnickel complex

The rotational spectrum of cyclopentadienylallylnickel, C₃H₅NiC₅H₅, has been studied using a pulsed molecular beam Fourier transform microwave spectrometer. Twelve a-type transitions were analyzed to obtain rotational and centrifugal distortion constants for the parent C₃H₅⁵⁸NiC₅H₅ complex. The measured rotational constant A = 3107.603(93) MHz is about 160.0 MHz larger than the predicted DFT value, providing evidence for possible fluxional motion in the complex. The large distortion constants, on the order of 100 kHz, provide further evidence for fluxional motion. The experimental constants B = 1302.38(22) and C = 1276.40(15) MHz are in good agreement with the DFT calculated values and confirm the η³-bonding of the allyl ligand to the Ni–C₅H₅ moiety. DFT calculations provide a V₅ barrier for internal rotation about the Ni–C₅H₅ axis of 53 cm⁻¹, with the lowest energy conformation having the central allyl c-atom eclipsed with respect to two C₅H₅ carbon atoms. Several additional rotational lines, possibly those of an exited torsional state, were observed but not assigned.     

The electronic spectrum of the triethylamine-perfluoro-tert-butanol complex

The far-ultraviolet absorption spectrum of the triethylamine-perfluoro-tert-butanol complex has been measured in the gas phase. The photoelectron band of lowest energy has also been determined. It is about 13000 cm^?1 higher than for free triethylamine. Up to at least 60000 cm^?1, the UV spectrum is readily interpreted as a triethylamine spectrum shifted to higher frequencies by about 13000 cm^?1. The bands of lowest frequency are the 3s and 3p Rydberg bands which follow the ionization potential. Up to 60000 cm^?1, no charge transfer type band has been found.     

Magnetic circular dichroism spectrum of the triphenylene-iodine complex

The MCD CT bands of the triphenylene (9,10-benzphenanthrene) -I₂, triphenylene-TCNE and I₂-I₂ complexes are indicative of a structure of C_3v symmetry where the I₂ is located centrally and axially over the triphenylene ring.     

Calculated electronic properties of medium sized sodium clusters: the inhomogeneous jellium model

Recently observed magic number data for Na _N clusters in the size range from 100 to 900 atoms cannot be fully explained by density functional calculations using a homogeneous, spherical positive charge background. However, a centrally compressed spherical background yields steps in the ionization potential at just those magic numbers observed experimentally.     

Microwave Fourier transform spectrum of the water-carbonyl sulfide complex

The microwave spectrum of the water-carbonyl sulfide complex H(2)O-OCS was observed with a pulsed-beam, Fabry-Perot cavity Fourier-transform microwave spectrometer. In addition to the normal isotopic form, we also measured the spectra of H(2)O-S(13)CO, H(2)O-(34)SCO, H(2) (18)O-SCO, D(2)O-SCO, D(2)O-S(13)CO, D(2)O-(34)SCO, HDO-SCO, HDO-S(13)CO, and HDO-(34)SCO. The rotational constants are B = 1522.0115(2) MHz and C = 1514.3302(2) MHz for H(2)O-SCO; B = 1511.9153(5) MHz and C = 1504.3346(5) MHz for H(2)O-S(13)CO; B = 1522.0215(3) MHz and C = 1514.3409(3) MHz for H(2)O-(34)SCO; B = 1435.9571(3) MHz and C = 1429.1296(4) MHz for H(2) (18)O-SCO, B = 1409.6575(5) MHz and C = 1397.9555(5) MHz for D(2)O-SCO; B = 1399.8956(3) MHz and C = 1388.3543(3) MHz for D(2)O-S(13)CO; B = 1409.6741(24) MHz and C = 1397.9775(24) MHz for D(2)O-(34)SCO; (B+C)/2 = 1457.9101(2) MHz for HDO-SCO; (B + C)/2 = 1448.0564(4) MHz for HDO-S(13)CO; and (B+C)/2 = 1457.9418(15) MHz for HDO-(34)SCO, with uncertainties corresponding to one standard deviation. The observed rotational constants for the sulfur-34 complexes are generally higher than those for the corresponding sulfur-32 isotopomers. The heavier isotopomers have smaller effective moments of inertia due to the smaller vibrational amplitude of the (34)S-C vibration (zero point) as compared to the (32)S-C, making the effective O-(34)S bond slightly shorter. Stark effect measurements for H(2)O-SCO give a dipole moment of 8.875(9)x10(-30) C m [2.6679(28) D]. The most probable structure of H(2)O-SCO is near C(2v) planar with the oxygen of water bonded to the sulfur of carbonyl sulfide. The oxygen-sulfur van der Waals bond length is determined to be 3.138(17) A, which is very close to the ab initio value of 3.144 A. The structures of the isoelectronic complexes H(2)O-SCO, H(2)O-CS(2), H(2)O-CO(2), and H(2)O-N(2)O are compared. The first two are linear and the others are T shaped with an O-C/O-N van der Waals bond, i.e., the oxygen of water bonds to the carbon and nitrogen of CO(2) and N(2)O, respectively.     

The complex dielectric spectrum of heart tissue during ischemia

INTRODUCTION: Because of the variety of tissue structures, the interpretation of the passive complex dielectric permittivity spectrum epsilon (omega) of the heart is still a problem. The aim of this work was to correlate epsilon (omega) of heart tissue with physical processes on cellular level. METHODS: epsilon (omega) of canine hearts was continuously measured in the range from 10 Hz to 400 MHz during cardioplegic perfusion and during following ischemia. Cardioplegic perfusion was performed with HTK (Custodiol) without or with heptanol, in order to produce electrical cell uncoupling via the closure of gap junctions. To analyse epsilon (omega), we present two heart models which consider cell shape, electrical cell coupling, and dielectric polarisation of cell membranes and membranes of intracellular structures. RESULTS: epsilon (omega) of heart tissue shows an alpha-, beta-, and gamma-dispersion. epsilon (omega) remains unchanged during cardioplegic perfusion with HTK, but if heptanol is added, there is an immediate decrease in the region of alpha-dispersion and an increase in the low frequency part of beta-dispersion. Similar changes are observed during ischemia following HTK perfusion without heptanol; additionally, the beta-dispersion shifts to higher frequencies. Using our models, we obtain analogue changes of epsilon (omega) by fitting model parameters which describe water content, water distribution, extra- and intracellular conductivity, and gap junction resistance. DISCUSSION: Changes of these tissue properties as calculated by our models based on the measurement of epsilon (omega) are consistent with intraischemic changes of heart tissue known from immunohistochemical, biochemical, and histological investigations. The next step will be to use our models for the prognosis of irreversible tissue damage.     

Infrared spectrum of the I- -D2 anion complex

The infrared spectrum of the I(-)-D(2) anion complex is measured in the D(2) stretch region by monitoring production of I(-) photofragments. The rotationally resolved spectrum consists of two overlapping Sigma-Sigma subbands, redshifted by approximately 58 cm(-1) from the free D(2) fundamental vibrational band. These subbands are associated with absorptions by I(-)-D(2) complexes containing ortho and para forms of D(2). The measured rotational constants are consistent with a 3.79 A separation between I(-) and the D(2) center of mass, contracting by 0.08 A when the D(2) subunit is vibrationally excited. Spectroscopic data are used to generate effective radial potential energy curves describing the interaction of ortho and para D(2) with I(-) from which the dissociation energies of I(-)-D(2)(ortho) and I(-)-D(2)(para) are estimated as D(0)=236 and 297 cm(-1), respectively.     

Luminescence spectrum and kinetics of laser-excited HgNH3 complex

When an Hg/NH₃ gas mixture was irradiated by laser light around 260 nm, luminescence appeared in the range of 290–360 nm. The spectrum of the luminescence was almost the same as that induced by the Hg photosensitized reaction of NH₃, and thus, the laser-induced luminescence was assigned to emission of an excited HgNH₃ complex. The luminescence spectrum as well as the excitation spectrum could be reproduced by the Franck-Condon factors calculated from the bound-free transition between the Hg-NH₃ repulsive ground state and the excited bound state. Time-evolution measurements on the luminescence induced by the pulsed irradiation of the laser indicated that initially formed HgNH₃ excimer had to make a collisional transition to a state which could emit the luminescence around 340 nm.     

High-resolution microwave spectrum of the weakly bound helium-pyridine complex

High-resolution rotational spectra of the helium-pyridine dimer were obtained using a pulsed molecular beam Fourier transform microwave spectrometer. Thirty-nine R-branch (14)N nuclear quadrupole hyperfine components of a- and c-type dipole transitions were observed and assigned. The following spectroscopic parameters were obtained: rotational constants A=3875.2093(48) MHz, B=3753.2514(45) MHz, and C=2978.4366(81) MHz; quartic centrifugal distortion constants D(J)=0.124 08(55) MHz, D(JK)=0.1200(43) MHz, D(K)=-0.2451(25) MHz, d(1)=0.004 27(27) MHz, and d(2)=0.000 16(10) MHz; sextic centrifugal distortion constants H(J)=0.003 053(35) MHz, H(JK)=-0.006 598(47) MHz, and H(K)=0.004 11(59) MHz; (14)N nuclear quadrupole coupling constants chi(aa)((14)N)=-4.7886(76) MHz, chi(bb)((14)N)=1.4471(76) MHz, and chi(cc)((14)N)=3.3415(43) MHz. Our analyses of the rotational and (14)N quadrupole coupling constants show that the He atom binds perpendicularly to the aromatic plane of C(5)H(5)N with a displacement angle of approximately 7.0 degrees away from the c axis of the pyridine monomer, toward the nitrogen atom. Results from an ab initio structure optimization on the second order Moller-Plesset level are consistent with this geometry and gave an equilibrium well depth of 86.7 cm(-1).     

Thermal lens spectrum of organic dyes using optical parametric oscillator

The wavelength dependence of thermal lens signal from organic dyes are studied using dual beam thermal lens technique. It is found that the profile of thermal lens spectrum widely differ from the conventional absorption spectrum in the case of rhodamine B unlike in the case of crystal violet. This is explained on the basis of varying contribution of nonradiative relaxations from the excited vibronic levels.