D Rostohar

The FERRUM Project: Experimental Transition Probabilities of [Fe II] and Astrophysical Applications

We report on experimental transition probabilities for thirteen forbidden (Fe II) lines originating from three dierent metastable Feii levels. Radiative lifetimes have been measured of two metastable states by applying a laser probing technique on a stored ion beam. Branching ratios for the radiative decay channels, i.e. M1 and E2 transitions, are derived from observed intensity ratios of forbidden lines in astrophysical spectra and compared with theoretical data. The lifetimes and branching ratios are combined to derive absolute transition probabilities, A-values. We present the first experimental lifetime values for the two Fe II levels a 4 G9=2 and b 2 H11=2 and A-values for 13 forbidden transitions from a 6 S5=2, a 4 G9=2 and b 4 D7=2 in the optical region. A discrepancy between the measured and calculated values of the lifetime for the b 2 H11=2 level is discussed in terms of level mixing. We have used the code CIV3 to calculate transition probabilities of the a 6 D-a 6 S transitions. We have also studied observational branching ratios for lines from 5 other metastable Fe II levels and compared them to calculated values. A consistency in the deviation between calibrated observational intensity ratios and theoretical branching ratios for lines in a wider wavelength region supports the use of (Fe II) lines for determination of reddening.

The FERRUM project: an extremely long radiative lifetime in Ti II measured in an ion storage ring

We have extended the laser probing technique at the CRYRING storage ring to measurement of the extremely long lifetime (28 s) of the metastable 3d2(3P)4s b 4P5/2 level in Ti II. The result obtained demonstrates the power of this method for investigation of such long-lived levels. This is the first experimental lifetime investigation of metastable states in Ti II.

Lifetime Measurements by Laser Probing in CRYRING – Recent Experimental Developments

A laser probing technique for lifetime measurements of long-lived metastable levels has been developed at the ion storage ring CRYRING. The method has been in use for about eight years and it has been applied to various ions. Levels with radiative lifetimes from a few milliseconds up to 28 s have been measured. The method has been continuously developed and this article is focused on recent experimental developments of the method in order to widen its applicability and to increase its efficiency and accuracy.

Rotational-temperature evolution of a N2+ ion beam in a storage ring probed by laser induced fluorescence spectroscopy

Laser induced fluorescence spectroscopy has been applied for the first time on a stored fast molecular ion beam. The rotational temperature of the N2+ ion beam was studied as a function of storage time. For up to 1 s of storage time, a temperature of 1040 K can be used to describe the rotational energy distribution.

Studies of Lifetimes in an Ion Storage Ring Using Laser Technique

The laser-probing method for lifetime measurements of metastable levels, performed by applying the Fast Ion Beam Laser (FIBLAS) method to ions stored in a storage ring, has been developed by the Stockholm group. Recently, we have applied this method to lifetime measurements of close lying metastable levels. In this paper we discuss experimental studies of ions with complex structure and present the first experimentally obtained lifetimes of selected metastable levels in complex systems as Fe+, Eu+ and La+.