| Description | Meeting held 16 and 17 January 2006 at the Royal Society
By Dr TR Geballe, Professor Dieter Gerlich, Professor Jonathan Tennyson and Professor Takeshi Oka FRS
H3+, the simplest polyatomic molecule, is widely observed in planetary atmospheres, and in a variety of interstellar clouds, most prominently near the Galactic center. H3+ is the most abundant molecular ion in the Universe and plays a pivotal role in interstellar chemistry. Laboratory experimentalists, theorists, and astronomers will meet to discuss scientific advances and problems involving this most interesting and important molecular ion.
This Discussion Meeting followed the great advance in the science of H3+ since 2000.
First principle calculations: Rigorous theory for rovibrational energy levels has been developed using the sub-microhartree accuracy potential of Kutzelnigg and colleagues and the hyperspherical coordinate formulation of Wolniewicz and Hinze. The latest calculation agrees with the experiment within ~ 1 cm-1 up to energy levels of ~ 12500 cm-1. Accurate ab initio calculations for the triplet state, the only bound electronic excited state, have been given by Alijah and colleagues. Tennyson has revealed asymptotic vibrational states of H3+ near the dissociation limit.
Laboratory spectroscopy: Overtone and combination bands have been extended to high energy levels beyond the barrier to linearity into the visible and given a critical test of theory. A new high sensitivity method called action spectroscopy has been invented by Schlemmer, Gerlich and colleagues and applied to H3+ and isotopomers. Submillimeter spectra of H2D+ and HD2+ have been measured by Amano.
Dissociative recombination: Larssons group has used rotationally cooled H3+ and obtained a most reliable recombination rate at the low temperature of interstellar space. Subsequent experiments by Wolf, Zajfman and colleagues using the TSR storage ring have given nearly identical results. A theoretical calculation by Kokooline and Greene has given values more than two orders of magnitude higher than in 2000 leading to the first agreement between theory and experiment.
Chemical kinetics: The cryo cooled 22-pole ion trap developed by Gerlich has been applied to the studies of H+ + H2 and H3+ + H2 reactions and their deuterium variants that are crucial for interstellar chemistry including spin statistics. The trap is also essential for the aforementioned action spectroscopy and used as the low temperature ion source for the measurement of dissociative recombination with the TSR ring.
High abundance in diffuse clouds: Contrary to expectation from model calculations, extensive observations by McCall, Geballe and colleagues of H3+ in diffuse clouds have established that the H3+ column density per unit visual extinction AV is an order of magnitude higher than in dense clouds, and that the total amount of H3+ in diffuse clouds is orders of magnitude higher than in dense clouds. This suggests that the cosmic ray ionization rate is an order of magnitude higher in diffuse clouds than in dense clouds. The value is beyond the limit set from HD and OH but Liszt has argued that such a high value of æ is favorable if neutralization of atomic ions on dust grains is taken into account.
The Central Molecular Zone (CMZ): Observations of H3+ toward the Galactic center by Geballe and colleagues is revealing existence of abundant H3+ in the CMZ. Large column densities of H3+ in the (J, K) = (3, 3) metastable levels were discovered by Goto et al. demonstrating high temperature of the environment. Subsequent observations and analysis has led to discovery of a vast amount of high temperature (~ 250 K) and low density (~ 100 cm-3) gas in the CMZ.
Ultra-high deuterium fractionation in proto-stars: A remarkable manifestation of the fundamental role H3+ plays in interstellar chemistry has been revealed in the high deuterium fractionation in protostars. Robert, Herbst and Millar have shown that in high density (> 106 cm-3) low temperature (10 K) clouds where molecules other than H2 are highly depleted, HD becomes the main destroyer of H3+ and the abundance of isotopomes is in the order of H3+ < H2D+ < HD2+ << D3+. This mechanism of high deuterium fractionation has been supported by the submillimeter detection of H2D+ in a prestellar core by Vastel, Phillips and Yoshida.
Dynamics in planetary ionospheres: It has been shown by Miller and colleagues that H3+ is not only a powerful probe for studying the hot plasmas in Jovian ionospheres, but it also plays a major role in the dynamics of giant planets through the ion-neutral coupling. With temperature of ~ 1100K, H3+ emission originating from v = 3 (T ~ 10,000 K) has been observed by Lellouch and colleagues.
Other advances: There have been many other inspiring developments rovibrational cooling, thermalization, electron heating, the role of H3+ as coolant in primordial star formation, as the electron donor in zero-metallicity stars, chemical model calculation of H3+ and isotopomers, etc. There also have been important progresses on related species such as H3, H3- H3++, H5+, H3+ (H2 )n etc. All of them were subjects of this Royal Society Discussion Meeting.
An archive of the talks and posters of this meeting is now available at http://h3plus.uiuc.edu/rs2006/program.html |