An anomaly in the isotopomer shift of the hyperfine spectrum of LiI

Abstract

A high-precision examination of the hyperfine spectrum of 6LiI in comparison with 7LiI shows a shift in the iodine nuclear electric quadrupole moment that cannot be accounted for by a model in which the electric field gradient at the iodine site is assumed to depend only upon the internuclear distance between Li and I. The other hyperfine interactions are consistent between the two isotopomers, including the previously reported electric hexadecapole interaction of the iodine nucleus.

Hyperfine spectra of KBr and KI

“…A few other 41 KI lines were also observed, confirming this shift, but were in situations where an accurate fit was not feasible. The shift is of the same type that we found earlier for LiI [8], but smaller. The fractional shift in eQq I00 in KI is 6.9 Â 10 À6 , compared to 7.239 Â 10 À5 for LiI.…”

“…As in the case of our previous investigation of LiI [8], where we found a similar term, we suspect that this is not a true hexadecapole but rather a ''pseudohexadecapole" resulting from the nuclear electric quadrupole perturbing the electron orbitals and these acting back on the same nucleus. Thyssen et al [19] calculated a value for the true hexadecapole interaction parameter in LiI that is three orders of magnitude smaller than our experimental value for that molecule, whereas a simple estimate of the pseudohexadecapole interaction Electric dipole moment (in debye) (l ij ) 0,0 11.064 ± 0.014 11.064 ± 0.014 1,0 0.049 ± 0.023 0.048 ± 0.023 a X ij denotes the coefficient in the expansion Xðv; JÞ ¼ P i;j X ij ðv þ 1=2Þ i ½JðJ þ 1Þ j .…”

“…In this paper, we present the results of an examination of the hyperfine spectra of the molecules KBr and KI, continuing our extended investigation [1][2][3][4][5][6][7][8][9][10] of alkali halide molecules using an electric resonance molecular beam spectrometer. The experimental details as they relate to the current experiments are described in a document included in Supplementary material.…”

Hyperfine spectrum of RbI

“…This compares with a shift of eQq 00 ðI in 6 Li 127 IÞ À eQq 00 ðI in 7 Li 127 IÞ ¼ þ14:07 AE 0:20 kHz that we reported in our study of LiI [9], and eQq 00 ðI in 41 K 127 IÞ À eQq 00 ðI in 39 K 127 IÞ ¼ À0:583 AE 0:012 kHz for KI [10]. It is notable that for all three of these molecules the eQq value of the iodine decreases (becoming more negative) with increasing mass of the other nucleus, and that the shift decreases with the smaller fractional change in the mass of the other.…”

Hyperfine spectrum of NaF

“…There are, however, additional considerations to take into account. Koch et al [13] have called attention to the need for calculation of a shift due to the electron penetration of the nucleus, and there is also the unexplained isotopologue anomaly that we identified in our spectrum of LiI [14], where the eQq of iodine was found to change with the change of lithium isotopes. Since we are not in a position to estimate these effects, we have not attempted to recalculate the sodium nuclear moment.…”