Molecular interactions are partitioned in SCF and correlation energy parts. It is shown that for atomic systems, one can join high quality ’’a priori’’ SCF calculations with a semiempirical estimate of the correlation energy, made using the standard long range multipolar expansion and corrected assuming the 3Σ+u state of H2 as a model (scaling the ’’size’’ of the atomic charge distribution as the ionization potential to the negative 2/3 power) to obtain very good agreement with the available experimental information.
High statistics calorimetric measurements of the β spectrum of 187 Re are being performed with arrays of silver perrhenate crystals operated at low temperature. After a modification of the experimental set-up, which allowed to substantially reduce the background of spurious counts and therefore to increase the sensitivity on the electron antineutrino mass, a new measurement with 10 silver perrhenate microbolometers is running since July 2002. The crystals have masses between 250 and 350 µg and their average FWHM energy resolution, constantly monitored by means of fluorescence X-rays, is of 28.3 eV at the β end-point. The Kurie plot collected during 4485 hours×mg effective running time has an end-point energy of 2466.1 ± 0.8stat ± 1.5syst eV, while the half lifetime of the decay is found to be 43.2 ± 0.2stat ± 0.1syst Gy. These values are the most precise obtained so far for 187 Re. From the fit of the Kurie plot we can deduce a value for the squared electron antineutrino mass m 2 νe of 147 ± 237stat ± 90syst eV 2 . The corresponding 90% C.L. upper limit for m νe is 21.7 eV. The interest in direct measurements of the neutrino mass m ν from the β decay spectrum has been recently stimulated by the evidence of a non zero value of ∆m 2 ν detected in searches on solar and atmospheric neutrino oscillations [1,2,3].Limits on direct measurements of m ν have been so far obtained by experiments with electrostatic spectrometers investigating the β decay of tritium. Recent results [4,5], have set an upper limit of 2.2 eV at 90% C.L. These experiments are based on the measurement of the spectrum of the emitted electron. One cannot therefore exclude "a priori" that the decay could partially occur on a excited state of the daughter molecule. This and other systematic effects have given in the past years a negative value for m ν 2 . Even if now these problems seem to be almost completely solved we think it is important to carry out a measurement in a different approach.Calorimetric measurements where all the energy released in the decay is recorded, appear therefore complementary to those carried out with spectrometers. In addition they allow to measure the entire β decay spectrum, and can therefore test any possible distortion of the Kurie plot. A particularly suitable approach appears the bolometric one [6,7] where detectors, operated at low * CEE fellow in the Network on Cryogenic Detectors, under contract FMRXCT980167 temperature, include absorbers of a material containing the β active nucleus. If the absorbers are diamagnetic and dielectric crystals their heat capacity can be very low, since it is proportional to the cube of the operating temperature. As a consequence even the tiny energy delivered by a particle can give rise to a measurable pulse in a suitable thermal sensor.The present experiment is carried out on the first forbidden unique decay:187 Re → 187 Os + e − + ν e which is particularly promising [8] due to its low transition energy (∼2.5 keV). In addition the large isotopic abundance of 187 Re (62.8 %) allows th...
Quantum and classical calculations of transport and relaxation cross sections in He-CO mixturesWe describe an infrared molecular beam spectrometer which uses a semiconductor diode laser and has been used to study the rotational relaxation of CO molecules in the free jet expansion of pure CO and a 90% He-\0% CO mixture. The data for the mixture are analyzed by means of a kinematical method based on the use of the master equation and empirically scaled state to state rate constants. Information of the He-CO rotationally inelastic rate constants are obtained. The possibility of using free jet expansion to study rotational inelastic collisions is discussed.
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