SPHERS: Spectroscopy of highly excitet rovibrational states

• Research unit: EU RFP
• Project number: 99.0031

Key words (English)

Laser spectroscopy; dipole moments; microwave spectroscopy; quantum beats

Alternative project number (English)

EU project number: HPRN-2000-00022

Research programs (English)

EU-programme: 5. Frame Research Programme - 4.1.1 Research training networks

Short description (English)

See abstract

Partners and International Organizations (English)

Coordinator: Bergische Universität Wuppertal (D)

Abstract (English)

The intensity of water absorption in the region of the solar spectrum plays a dominant role in atmospheric energy balance and hence strongly influences climate. Significant controversy exists over how to model this absorption accurately. We report dipole moment measurements of highly vibrationally excited water, which provide stringent tests of intensities determined by other means. Our measurements, together with calculations performed by our partners in this network, suggest that the best currently available potential and dipole surfaces do not accurately model intensities in the optical spectrum of water.

Dipole moments of vibrationally excited water have been measured using a novel time-domain quantum beat technique. This approach relies on the ability to coherently excite the M sublevels of a Stark multiplet at a given time with a polarized, 7 nanosecond laser pulse, and subsequently probe their time evolution after a prescribed delay with a second polarized laser. The time evolution depends on the Stark splitting of the multiplets, which in turn depends on the dipole moment and the applied electric field; hence the dipole moment can be determined. The probe step is accomplished by excitation of the vibrationally excited molecule to a dissociative electronic state. In the case of water, a laser coherently prepares a single rotational state of a high OH stretching level of water. After a prescribed delay, a second laser dissociates the excited molecules with a probability that depends on the coherent evolution of the different Stark components. Finally a third laser probes the appearance of OH fragments by laser-induced fluorescence. Measuring the dependence on the electric field allows one to determine the dipole moment of highly excited water.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 99.0031