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MPINP:
Quantendynamik - Abteilung Blaum
Abstract:
The Heidelberg electrostatic Cryogenic Storage Ring (CSR) [32] provides an environment
for storing ion beams up to hours under interstellar conditions. A low
radiative background and a residual particle density of < 140 cm-3 is achieved
by cooling the experimental chambers of the CSR down to 6 K by liquid helium.
In such an environment internally excited infrared-active molecules cool to their
lowest rovibrational levels by emitting photons. The radiative cooling of a rotationally
hot OH- beam at 60 keV is probed by near-threshold photodetachment.
Thereby the radiative lifetimes of the lowest rotational states (193(3)stat(3) )sys)s
for J = 1) are measured directly by the exponential decays and the rotational
transition dipole moment is determined. Calculations [84, 90] for the transition
dipole moment in the vibrational ground state deviate about (7 +/- 1)% from the
experimental value of dv=0 = 0:971(10) D. The correlation between the rotational
energy levels and their corresponding radiative lifetimes is used to reveal the individual
level populations and their relative photodetachment cross sections. In
the steady state an internally cold OH- beam is reached with more than 90%
of the population in the rovibrational ground state, corresponding to an effective
internal temperature of 15 K.
