**Principal Investigator**
E von Nagy-Felsobuki **Project** g19

Department of Chemistry **Machine** VP

The University of Newcastle

**Rovibrational Calculations of Bent Triatomic Molecules**

The aim of this project is to carry out a thorough and systematic investigation of the electronic and structural properties of the ground and excited states of the XY+n and XY2+n ions ( where X is a first, second or third row atom and Y is a first, second or row atom). The initial focus of the project centred on the alkali metal vapours since they have been predicted to be important in the development of new arc lamps, flash lamps, high resolution optically pumped lasers, continuous wave tunable infrared lasers, solar pumped lasers, discharge pump high energy laser or laser amplifiers and infrared photography. They are also expected to be used as coolants, as shields for fusion reactors, in neutral beam injection charge exchange cells and as an alternative source for negative ions in neutral beam injection.

**What are the basic questions addressed?**

The specific aim is to calculate potential energy surfaces of ground and excited states of the XY+n and XY2+n ions in order to determine their rotationally resolved infrared spectrum. Attention is also focused on calculating ab initio vibrational-rotational eigenenergies as well as evaluating rovibrational transitional probabilities. This will enable an assessment of the dominant transitions in this ions.

The initial research centred on the alkali metal vapours. The following basic questions were addressed.

(a) What are the strategies required to accurately solve the 'complete' Schrodinger problem? Attempts to solve the 'complete' molecular Schrodinger equation are not common place, even with the advent of supercomputers.

(b) What lasing states exist for the alkali metal vapours?

(c) What are their electronic and rovibrational properties?

(d) How can the above information be translated into developing new technologies?

**What are the results to date and future of the
work?**

The project was initially funded in 1992. the project is progressing well with the potential energy surfaces and rovibtational states of a number of alkali metal ions being characterised (as well as the rovibrational states of the water cation). Since 1992 ther have been a number of papers published in international journals conference papers and a number of successful post-graduate research projects arising from access to the VP2200. Moreover, a monograph has been published which summarizes the work completed to-date.

Work will now focus on the ground electronic adn excited states of the XY+n and XY2+n ions (where X = C, N, O, F AND Y = He of Ne) in order to determine their rotationally resolved infrared spectrum. Some preliminary results have already been reported.

**What computational techniques are used and why
is a supercomputer required?**

Solving the electronic Schrodinger eigenvalue problem for electron dense systems is at present an open-ended problem. To that end the GAUSSIAN suite of programmes enable 'effective' truncations to be made to force tractable solutions. Using the GAUSSIAN programmes with valence double zeta (+polarisation) basis sets coupled with CCD, SDCI or MP4 level of theory enables computation of ab initio discrete potential energy surfaces of spectroscopic quality. For example, the computation time required to produce just one surface with a total of 50 points consumes at least 60 SU. Therefore five discrete electronic surfaces would require c.a. 300 SU.

**Publications**

*Ab Initio Rovibrational States of D3h
amd C2v *
*Isotopomers of Li**3 +, *
F. Wang and E. I. von Nagy-Felsobuki, Spectrochimica Acta,