POSTER ABSTRACTS

There has been great interest in H3+ in its electronic triplet state for a long time. The lowest triplet state is known to possess shallow minima, but it has been an open question of how many bound vibrational states it might support.

The two lowest potential energy hypersurfaces of triplet H3+, which show a conical intersection, have now been calculated to high accuracy [1] using a cc-pV5Z basis set. Two different representations of the potential energy hypersurfaces have been obtained: a global representation of the two electronic states and a local representation of the lower state around the minimum. First calculations of the bound vibrational states, using our method of hyperspherical harmonics [2], indicate that there may exist as many as 8 vibrational states on the lower electronic potential energy hypersurface: three of A1 symmetry, one of A2 symmetry and four of E symmetry. Work is still in progress, and we expect to present more data on the ro-vibrational states at the conference.

[1] O. Friedrich, doctoral thesis, Bielefeld (2000)

[2] A. Alijah, L. Wolniewicz and J. Hinze, Mol. Phys. 85, 1125 (1995)

We have carried out a detailed experimental study of the dissociative recombination rates of H3+ ions and several other interstellar ions using our FALP apparatus, addressing several potential experimental difficulties. Thus, we have shown that vibrationally relaxed H3+ ions recombine slowly, the recombination coefficient for H3+(v=0) being (1-2)x10-8 cm3s-1 at 300 K, whilst H3+(v=3) ions recombine more rapidly (1.3x10-7 cm3s-1 at 300 K). Additional measurements at 210 K and 140 K indicated a slow increase of the H3+ recombination coefficient with decreasing temperature down to 140 K. The measured recombination coefficients for D3+ ions are smaller by a factor of about 1.4 within the same temperature range. We have also measured the recombination coefficients for the interstellar ions HCO+, N2H+ and CH5+ under identical experimental conditions, clearly showing that these ions recombine more rapidly than H3+ ions.

(1) IAP, Paris, France
(2) Observatoire de Paris, Meudon, France
(3) SWRI, San Antonio, Texas, USA
(4) Universite Paris 6, Paris, France

In Oct. 1998 and Sept. 1999, observations of the Northern and Southern auroral regions of Jupiter in the nu2 fundamental band of H3+ were conducted with the FTS at the CFH Telescope. The spectra which cover the range 2465-2580 cm-1 were acquired for most of them with a resolution of 75,000 i.e. 4 km/s in velocity. This high resolution was aimed at searching for ionospheric winds from absolute measurements of Doppler shifts of the H3+ lines. The spectra were acquired with a 2.5'' circular aperture, successively centered in 1998 on the limbs and the LMC, while in 1999 series of spectra were acquired on the Southern LMC (LIII= 20-145 deg). Ten lines of each spectrum were fitted with a line-fitting programme specially adapted to FTS spectra. The final line positions were compared to high resolution lab measurements of the same band from McKellar and Watson (1998). From the data of 1998 a general sunward wind < 1 km/s of the Southern oval was detected while a poleward wind of 1.9 km/s on the Northern LMC with a sunward wind of 0.9 km/s at the Eastern limb (Western limb missing) was measured suggesting opposite jets. The spectra of 1999 show a modulated meridional winds of amplitude < 1 km/s in the Southern oval. More observations and theoretical works are needed to explain this behavior.

The high J P(12,12)+ transition (J'=11, G=12, U=+1 <- J=12, K=12) of H3+ has been observed using a tunable diode in the 6.5 micron region. The observed wavenumber of the transition, 1546.901 cm-1, is the lowest ever observed for H3+. It is higher than the predicted value [1] by 0.782 cm-1. In order to produce rotationally hot H3+ ions, an air cooled 6 kHz ac glow discharge with a gas mixture of H2:He = 1.2:5.0 torr was used. The J=12 K=12 level is 3340 cm-1 above the lowest rotational level. The velocity modulation method was used to increase the sensitivity. The spectral line was observed with the signa to noise ratio of ~10. This sensitivity is two orders of magnitude lower than that required to observe the stronger H3+ forbidden rotational transition predicted at 300-800 cm-1 [2,3].
1. J.K.G.Watson, private communication
2. F.-S.Pan and T.Oka, Ap.J.305,518(1986)
3. S.Miller and J.Tennyson, Ap.J.335,486(1988)

The ionization fraction of molecular clouds is an important parameter for their chemistry as well as for their dynamics. Cosmic rays dominate the ionization, but their rate has so far only been inferred indirectly from chemical modeling. The recent detections of H3+ infrared absorption lines by Geballe & Oka (1996) and McCall et al. (1999) towards massive protostars enable us to measure the ionization rate directly.

The temperature and density structure of the sources in which H3+ has been detected has been accurately modeled by van der Tak et al. (1999, 2000) based on submillimeter continuum and line observations. These models predict directly the column density and excitation temperature of H3+, and by comparison to the infrared data, the cosmic ray ionization rate can be determined directly. We discuss possible origins of the source-to-source variation in the ionization rate, and if additional ionization by stellar UV or X-ray emission plays a role.

Most of a large gap in the laboratory observations of H3+ ro-vibrational transitions around 4000 cm-1 is being filled using a recently computer controlled color center laser spectrometer scanning between 3000 and 4200 cm-1. A liquid nitrogen cooled He/H2 discharge is used to produce rotationally cool, yet vibrationally hot H3+. Variational calculations1 predict approximately 75 new lines from the fundamental, the first overtone, combination, and hot bands to be observable at the sensitivity of our spectrometer. Our progress in this survey is reported.

It has been assumed from an order of magnitude calculation that ambipolar diffusion to the wall and then recombination with electrons at the wall has the rate of 105 - 106 s-1 and is the dominant destruction path for molecular ions in positive column discharges. We have developed a method to observe such destruction rates experimentally based on the competition between the ambipolar diffusion rate and the destruction rate by added impurities. The decrease of a velocity modulated H3+ absorption signal was studied when small amounts of CH4, N2, and CO were added to a pure hydrogen AC positive column discharge. The destruction rate constant of H3+ due to ambipolar diffusion was then obtained using a steady state model and previously reported ion-neutral reaction rate constants. The ambipolar diffusion destruction rate constant for H3+ in a 1.2 cm diameter bore discharge tube was measured to be (8.7 +/- 1.8) x 10^5 s-1.

Hydrogen is by far the most abundant element in the universe. Chemistry in space is therefore largely governed by its chemistry, and specially when it is in its ionized H3+ form. Because of the major role played by this ion, we have investigated some aspects of its space chemistry using accurate methods of Quantum Chemistry. In this presentation we will report on the photodissociation of H3+, the protonation of molecules by H3+, and the search for possible stable ion-pair molecules of H3+ - X- type.