204 J. Opt. Soc. Am./Vol. 71, No. 2/February 1981 JOSA Letters

Revised 6p 2P1/2 level of Mo xiv

Joseph Reader, Gabriel Luther, and Nicolo Acquista

National Bureau of Standards, Washington, D.C. 20234

Received August 22, 1980 New observations of the 4s-6p transitions of Mo XIV have led to a revised identification for the 4d 2D3/2-6p 2P1/2 transition and a revised value for the 6p 2P1/2 level.

The 6p 2 P 1 / 2 , 3 / 2 levels of the copperlike ion Mo XIV were given originally by Alexander etal.1 based on their observation of the 4s-6p transitions at 61 A. Our recent spectral obser­vations2 of this ion with a 10.7-m spectrograph at an angle of incidence of 80° did not extend below 70 A, and thus we were not able to make new measurements of these transitions. We instead determined the value of the 6p levels by means of the 4d-6p transitions at 101 A. In this process, we first obtained an accurate value for the 6p 2P3/2 level by identifying the Ad 2D5 /2-6p 2 P 3 / 2 and Ad 2D3 /2-6p 2 P 3 / 2 transitions. The 6p 2 P interval of Ref. 1 was then used to help identify the Ad 2D3/2 -6p 2 P 1 / 2 transition (101.663 A), which thus provided an ac­curate value for the 6p 2 P 1 / 2 level.

We have now made new observations of the Mo XIV spec­trum with a low-inductance spark and laser-produced plasma using the 10.7-m spectrograph at an angle of incidence of 85° and a 2.2-m spectrograph at an angle of incidence of 86°. The 4s-6p transitions stand out clearly on these spectrograms. Measurement of their wavelengths against reference lines of Fe and Mo yields wavelengths of 60.975 and 61.229 A for these lines and a value for the 6p 2 P fine-structure interval of 6800 ± 80 cm - 1 . This is to be compared with our published2,3 value of 6431 ± 30 cm"1 and the value in Ref. 1 of 6550 cm - 1 . The new value compares well with the semiempirical value of 6813 c m - 1 given by Curtis.4

The new value of the 6p 2 P interval leads us to re-identify the 4d 2D3 / 2-6p 2 P 1 / 2 transition as a line in our earlier obser­vations2 at 101.699 A (intensity = 15). Revised values of several quantities associated with the 6p 2 P 1 / 2 level are given in Table 1. The value of the 6p 2 P interval given in this table is that determined from the 4d-6p transitions. As the

Table 1. Revised Values of Quantities Associated with the 6p 2 P 1 / 2 Level of Mo XIV

Mo XIV ionization energy2 was determined from the ng series (n= 5 to n = 7), the ionization energy is not affected by the revised value of the 4p-6p series limit.

REFERENCES 1. E. Alexander et al., "Classification of transitions in the euv spectra

of YIX-XIII, Zr X-XIV, Nb Xl-XV, and Mo xπ-XVl," J. Opt. Soc. Am. 61, 508-514 (1971).

2. J. Reader, G. Luther, and N. Acquista, "Spectrum and energy levels of thirteen-times ionized molybdenum (Mo Xiv)," J. Opt. Soc. Am. 69, 144-149 (1979).

3. The uncertainty in the published value derives from an estimated uncertainty of ±0.003 A in the relative wavelengths of the 4d-6p transitions.

4. L. J. Curtis, "An explicit empirical formula for fine-structure separations of 2P and 2D terms for ions in the Cu isoelectronic se­quence," J. Phys. B (to be published).