A2 Pi Research Articles

Radiation thermo-chemical models of protoplanetary discs

The carbon monoxide rovibrational emission from discs around Herbig Ae stars and T Tauri stars with strong ultraviolet emissions suggests that fluorescence pumping from the ground X1 Sigma+ to the electronic A1 Pi state of CO should be taken into account in disc models. We implemented a CO model molecule that includes up to 50 rotational levels within nine vibrational levels for the ground and A excited states in the radiative photochemical code ProDiMo. We took CO collisions with hydrogen molecules, hydrogen atoms, helium, and electrons into account. We estimated the missing collision rates using standard scaling laws and discussed their limitations. UV fluorescence and IR pumping impact on the population of ro-vibrational v > 1 levels. The v = 1 rotational levels are populated at rotational temperatures between the radiation temperature around 4.6 micron and the gas kinetic temperature. The UV pumping efficiency increases with decreasing disc mass. The consequence is that the vibrational temperatures, which measure the relative populations between the vibrational levels, are higher than the disc gas kinetic temperatures (suprathermal population). Rotational temperatures from fundamental transitions derived using optically thick 12CO lines do not reflect the gas kinetic temperature. CO pure rotational levels with energies lower than 1000 K are populated in LTE but are sensitive to a number of vibrational levels included in the model. The 12CO pure rotational lines are highly optically thick for transition from levels up to Eupper=2000 K. (abridged)

A fresh look at η 2(1645), η 2(1870), η 2(2030) and f 2(1910) in $\bar{p}p \to \eta \pi ^{0}\pi ^{0}\pi ^{0}$

There is a large discrepancy between results of Crystal Barrel and WA102 for the branching ratio R = BR[eta2(1870)->a2(1320)pi]/ BR[eta2(1870)->f2(1270)eta]. An extensive re-analysis of the Crystal Barrel data redetermines branching ratios for decays of eta2(1870), eta2(1645), eta2(2030) and f2(1910). This re-analysis confirms a small value for R of 1.60+-0.39, inconsistent with the value 32.6+-12.6 of WA102. The likely origin of the discrepancy is that the WA102 data contain a strong f2(1910)->a2-pi signal as well as eta2(1870). There is strong evidence that the eta2(1870) has resonant phase variation. A peak in f2(1270)a0(980) confirms closely the parameters of the a2(2255) resonance observed previously. A peak in eta2(2030)-pi is interpreted naturally in terms of pi2(2245) with reduced errors for mass and width M=2285+-20(stat)+-25(syst) MeV, Gamma=250+-20(stat)+-25(syst) MeV.

The VUV electronic spectroscopy of acetone studied by synchrotron radiation

The electronic state spectroscopy of acetone (CH3)2CO has been investigated using high-resolution VUV photoabsorption spectroscopy in the energy range 3.7-10.8 eV. New vibronic structure has been observed, notably in the low energy absorption band assigned to the 1(1)A(1) --> 1(1)A2 (ny --> pi*) transition. The local absorption maximum at 7.85 eV has been tentatively attributed to the 4(1)A1 (pi --> pi*) transition. Six Rydberg series converging to the lowest ionisation energy (9.708 eV) have been assigned as well as a newly-resolved ns Rydberg series converging to the first ionic excited state (12.590 eV). Rydberg orbitals of each series have been classified according to the magnitude of the quantum defect (delta) and are extended to higher quantum numbers than in the previous analyses.

Purification and Analysis of Abscisic Acid-Specifically-Inducible Proteins from Rice Callus

Two ABA-specifically-inducible proteins from rice callus were isolated and purified by precipitation with 65–100% saturated (NH 4) 2SO 4, followed by the DEAE-sepharose, TSK-gel, and two-dimension electrophoresis. Iso-electric points (pI) of the proteins with the same molecular mass (24.5 kD) were 6.1 and 6.9, respectively. The Western blot analysis indicated that the proteins expressed in different tissues were obviously different. The A1 (pI 6.1) protein was only detected in calli treated with ABA and seed embryos (SE). However, the A2 (pI 6.9) protein was found not only in the calli treated with ABA and SE, but also in the white dry callus. Thus it suggested that the two proteins might play some important roles in the processes of seed embryo (or somatic embryo) formation.

An extensin peroxidase is associated with white-light inhibition of lupin (Lupinus albus) hypocotyl growth

The spatial distribution of the major basic (B2; pI 8.8) peroxidase of the intercellular fluid has an inverse relation with extension rate in etiolated hypocotyls of Lupinus albus L., suggesting its possible role in the control of cell expansion. White-light irradiation of etiolated hypocotyls resulted in growth inhibition and the induction of B2 and acidic (A2, pI 4.7–5.2) isoperoxidases (EC 1.1.11.7) to higher physiological activities. However, only the activities of the B2 isoperoxidases underwent quantitative changes in both space and time which suggested their role in growth-retardation. We have purified the B2 and A2 (pI 5.2) peroxidases to apparent electrophoretic homogeneity. To corroborate evidence obtained elsewhere that growth cessation coincides with cell wall structural changes and cell wall rigidification, we have shown that the B2 peroxidase, and not A2 peroxidase, cross-links tomato extensin in vitro. The B2 peroxidase may therefore catalyse the developmentally and light regulated formation of a covalently cross-linked cell wall extensin matrix in lupin hypocotyls. The cell wall would be more rigid or more recalcitrant to wall-loosening and subsequently contribute to the control of cell expansion.

The relationship betwen smoking and triglyceride-rich lipoproteins is modulated by genetic variation in the glycoprotein IIIa gene

In the last year, several studies have reported conflicting results concerning an association between the PI A2 allele of the PI A1 A2 polymorphism of platelet glycoprotein IIIa and the risk of myocardial infarction. In the present study, we analyzed the hypothesis of whether glycoprotein IIIa genotypes have any association with lipids and lipoproteins as classical cardiovascular risk factors. Smoking, associated with changes in triglyceride-rich lipoprotein (TRL) concentrations and with both hypercoagulability and reduced fibrinolysis, was also analyzed as an environmental factor. Blood samples were obtained from 170 subjects (83 men and 87 women; mean age, 57 years; SD 15) recruited by random sampling from the census of Girona, Spain. Subjects were classified as current smokers (n = 41) and nonsmokers or exsmokers (n = 129). Whereas no differences were found in lipid and lipoprotein concentrations between smokers and nonsmokers in subjects with the PI A1 A1 genotype, smokers with the PI A1 A2 or PI A2 A2 genotypes showed significantly higher triglyceride and very—low-density lipoprotein (VLDL) triglyceride concentrations than nonsmokers or exsmokers with the same genotypes. Similarly, the VLDL triglyceride/HDL cholesterol ratio was significantly different in subjects with the PI A1 A2 or PI A2 A2 genotypes stratified according to smoking status. Further analysis revealed a significant interaction between smoking and genotype when those homozygous for the allele PI A1 were compared with one or two PI A2 alleles for the three lipid parameters. The observed effects appear to show links between smoking, triglyceride metabolism, and a glycoprotein involved in platelet aggregation. It is likely that the PI A polymorphism is in linkage disequilibrium with other functional mutations that might influence triglyceride metabolism under some environmental factors such as smoking. This finding may provide a new perspective in the complex relationship between glycoprotein IIIa gene, environment, and their interactions.

Coupling of molecular spin in electron-molecule scattering

We consider spin-dependent effects in low-energy electron molecule scattering. Until now no explicit spin dependent effects have been included in ab initio calculations. We discuss the fine-structure effect, well known from atomic physics, for diatomic molecules as a model which can describe deviations from pure exchange scattering. Numerical results for the a3 Pi excitation of CO will give an indication of the magnitude of the effects. Resolving the fine-structure of the target leads to the different coupling schemes for diatomic molecules. We consider in this paper Hund`s cases (a) and (b) as the two most important ones. In particular, differential cross sections and spin polarization for unpolarized projectiles and targets are discussed. For molecules obeying Hund`s case (a) coupling scheme orientation and alignment parameters are introduced.

Relative photoionization cross section study of OH and OD from 68 nm to 95 nm

The photoionization spectra of OH and OD have been reported from 680 to 950 AA (18.23 to 13.05 eV) at a wavelength resolution of 0.07 AA. Through interpretation of both spectra, the Rydberg series and their higher vibrational members have been reported for three of the excited ionic states, a1 Delta , A3 Pi i, and b1 Sigma +. A vibrational progression has also been observed in both OH and OD which is apparently related to a fourth excited ionic state, c1 Pi . Finally, the dissociative ionization limits, corrected to 0 K, for H2O and D2O have been measured to be 18.11+or-0.01 and 18.21+or-0.01 eV, respectively, and shown to be in good agreement with previously reported results.

Coherent excitation of Lambda -doublet states of heteronuclear molecules by electron impact

We consider the rotationally resolved excitation of heteronuclear diatomic molecules. Particular emphasis is on the selective population of the Lambda -doublet states and their coherence properties produced during the collision. The general theory is developed and the relevant selection rules are derived. Using recently obtained T-matrix elements for the a3 Pi excitation of CO we have calculated the relevant parameters of interest for several energies as a function of the scattering angle. The results show that the epsilon =+1 members of the Lambda -doublet states are preferentially excited for small and large scattering angles. It is shown that a considerable amount of coherence between the Lambda -doublet states is produced which is responsible for a nonvanishing electric dipole moment induced by the collision.

Absorption and stimulated emission between the electronic states of C and C2 radicals in an expanding thermal plasma

Using the method of reabsorption the absolute densities of argon, atomic and molecular carbon are determined during the deposition of amorphous hydrogenated (diamond-like) carbon coatings by an expanding thermal are plasma. Depending on the gas mixture argon/methane or argon/acetylene and the manner of hydrocarbon injection, the stationary negative or positive absorption between the quantum states Ar(3p54p to 3p54s). C(2p3s to 2p2) and C2(d3 Pi g, v'=0 to a3 Pi u, v''=0) were obtained. From the line absorption the absolute population densities of the radicals in the plasma have been determined. The density of the argon first excited state Ar(3p54s, 3P2) is approximately=1016-1017 m-3 the atomic and diatomic molecular carbon densities are of the order of 1018-1019 m-3.

Synchrotron radiation study of photoionization and photodissociation processes of CO2 in the 13-21 eV region

A study of synchrotron radiation induced photoionization and photodissociation of CO2 has been performed using the Swedish national synchrotron facility Max in Lund. Monochromatic synchrotron radiation, in the 10-30 eV region, has been used to obtain mass spectra of the CO2+, CO+, O+, and C+ ions. The observed structure is interpreted in terms of autoionization and photodissociation processes via excited Rydberg states in CO2 converging to the ionic X2 Pi g, A2 Pi u, B2 Sigma u+, and C2 Sigma u+ states. In the CO2+ ion yield measurements, new progressions are assigned as members of a Rydberg series converging to the A-state for which only the n*=2.5 member has been observed before. A transition to the bent valence state has been recorded and discussed. Fluorescence spectra obtained in the visible and VUV regions support ion yield results. Furthermore, structures originating from resonant autoionization have been found.

Collisional excitation of CO by slow molecular ions: wavefunction overlap effects

High-resolution translational-energy spectrometry has been applied to study excitation of CO molecules in 1.8 keV collisions with H2+, N2+, CO+, CO2+, O2+ and CS2+ projectiles. Transitions to the optically forbidden triplet states a3 Pi and a'3 Sigma +, optically allowed states A 1 Pi , B 1 Sigma + and G 1 Pi , and ionizing transitions to the low-lying states of CO+, X2 Sigma +, A 2 Pi and B 2 Sigma +, are observed. Oscillator strengths for electronic transitions to individual states are obtained by simulating the measured energy-loss spectra with calculations using either spectroscopically determined or calculated Franck-Condon factors. Wavefunction overlap effects manifest themselves in the observation that the cross section for collisional excitation of CO is found to be sensitively dependent on whether the molecular projectile ion possesses Sigma or Pi symmetry. Excitation cross sections are at least a factor of 10 larger in the case of Sigma projectiles.

Spectroscopic diagnosis of vibrationally-hot N2

Electron-impact induced VUV emission measurements of the C'41 Sigma +u-X1 Sigma g+ and a1 Pi g-X1 Sigma g+ systems of N2 allow significant information about the vibrational character of an RF excited N2 beam to be obtained. The former system provides a rather accurate direct monitor of the v=0 population of the ground state whereas the latter allows conclusions to be drawn about the population in other states as well. The relative quantum efficiency of a CCD-based detection system used in some of the measurements is also established.

Excitation of the electronic states of carbon monoxide by electron impact

Differential cross sections for the electron scattering processes: X1 Sigma + to X1 Sigma +, a3 Pi , a'3 Sigma +, (d3 Delta i+e3 Sigma -+I1 Sigma -+D1 Delta ), A1 Pi , b3 Sigma +, B1 Sigma +, j3 Sigma +, (C1 Sigma ++c3 Pi ) and E1 Pi in CO have been determined for incident electron energies 20, 30, 40 and 50 eV. These differential cross sections were obtained for the scattered electron angle range 10-90 degrees by analysing electron-energy-loss spectra in CO at a number of fixed scattering angles within that range. To the best of the authors' knowledge the present study represents the first comprehensive investigation of electron impact excitation of the electronic states of CO to be thus far reported in the literature.

Quenching rates of N2(a1 Pi g) vibrational levels from v'=3 to v'=6

The quenching rates of N2(a1 Pi g, v'=3-6) by molecular nitrogen are measured in the time afterglow of a pulsed low-pressure nitrogen discharge. The following quenching rate coefficients were estimated: KQ(3)=(3.42+or-0.3)*10-11 cm3 s-1, KQ(4)=(9.16+or-0.9)*10-11 cm3 s-1, KQ(5)=(15.3+or-1.3)*10-11 cm3 s-1 and KQ(6) approximately=22*10-11 cm3 s-1 for v'=3-6 respectively.

Configuration interaction calculations on the X1 Sigma + ground state and low-lying A1 Pi and 1 Delta excited states of the PN molecule. I. Potential energy curve of the X1 Sigma + state of PN. Miscellaneous spectroscopic observables

A series of multireference configuration interaction (CI) calculations using an extended Gaussian basis set have been performed on the X1 Sigma + ground state of the PN molecule in order to accurately determine the potential energy surface in the vicinity of the minimum. With the help of this curve a wide assortment of spectroscopic observables have been computed. The overall agreement with experiment is good. Marked correlation energy effects are found for the electric dipole/quadrupole moments and nitrogen nuclear coupling. Pure rotational excitations calculated by means of the numerical solutions of the radial Schrodinger equation are found to be in quite good agreement with experiment. Average values of the electric dipole moment over the first vibrational levels have been derived and the trend exhibited by the experimental data is well reflected by the theoretical results. Vibrorotational transitions, pure vibrational and vibrorotational lifetimes have also been determined which, to date, have not been determined experimentally.

Relaxation of metastable N2 (a1 Pi g, V'=0-2) in nitrogen afterglow

The relaxation rate of N2(a1 Pi g, v'=0-2) singlet metastable state is observed from the emission of a1 Pi g-X1 Sigma g+ bands in a nitrogen time afterglow. The quenching rates k0=0.91+or-0.05, k1=1.64+or-0.048 and k2=2.12+or-0.055 (*10-11cm3 s-1) and the radiative lifetime tau 0=54.2+or-6.5 mu s, tau 1=55.9+or-6.0 mu s and t2=54.1+or-5.8 mu s are deduced from the linear part of the dependences of the time decay against pressure.

Vibrational distribution of N2(a1 Pi g) in a DC glow discharge

The vibrational distribution of the singlet metastable state N2(a1 Pi g) was measured in a DC glow discharge by optical emission spectroscopy of the Lyman-Birge-Hopfield bands in the VUV range. The pressure ranged from 4 mTorr to 2 Torr and the current from 5 to 50 mA. The observed distribution is strongly non-Boltzmann. A population inversion similar to that in aurora was observed at low pressure and low current but not at higher pressures. The experimental results are compared with a kinetic model based on solutions to the electron Boltzmann equation and the rate balance equations for the N2(a1 Pi g) vibrational levels.

Measurement of the lifetime of metastable species by electron impact dissociation of molecules

Electron impact dissociative excitation of molecules is used to measure the lifetime of metastable species which cannot easily be produced in the laboratory by direct excitation. Two illustrative examples are given. The lifetime of the N2(a1 Pi g) state is measured to be 120+or-2 mu s and the lifetime of the O(5S) state to be 185+or-30 mu s, both in good agreement with earlier measurements. The method described may be extended to many other metastable species of current interest.

Acidic ribosomal proteins of Dictyostelium discoideum that show electrophoretic similarity to Escherichia coli proteins L7 and L12

This study documents the presence of three acidic proteins, A1 (pI 4.95), A2 (pI 4.85), and A3 (pI 4.70), in Dictyostelium discoideum ribosomes. All three proteins showed an apparent molecular mass of 13,000 by two-dimensional, sodium dodecyl sulfate gel electrophoresis. They were selectively released by treatment of ribosomes with 50% ethanol -1 M NH4Cl. The amino acid composition of A1, A2, and A3 were identical and indicated a predominant amount of alanine. All the above properties are shared by Escherichia coli proteins L7 and L12 and acidic ribosomal proteins in many eukaryotes. Unlike other eukaryotic systems, the acidic proteins of D. discoideum were found associated with the 40S rather than the 60S ribosomal subunit. Acidic proteins analogous in size and electrophoretic mobility to those of D. discoideum were also detected in several other cellular slime mold strains. Not one of the cellular slime mold acidic proteins reacted with antibodies to E. coli proteins L7 and L12 in immunodiffusion tests. In D. discoideum, the distribution of acidic proteins was altered during development. Amoebae contained all three proteins. In spores, A1 was absent and the relative amounts of A2 and A3 were lower than in amoebae. In addition, nine other acidic ribosomal proteins exhibited differences between vegetative amoebae and spores.