M. D. Allen

The pure rotational spectrum of FeC (X3Δi)

The pure rotational spectrum of the FeC radical (X3Δi) has been measured in the laboratory for the first time using millimeter/submillimeter direct absorption techniques. FeC was created by the reaction of iron vapor, produced in a high-temperature Broida-type oven, and methane gas under DC discharge conditions. Six rotational transitions each were recorded for the two lower spin-orbit ladders of this molecule in the frequency range 240-484 GHz, as well as six transitions for the Ω = 3 ladder of the iron isotopomer 54FeC. The data were analyzed using a3Δ Hamiltonian, and rotational and certain spin-orbit parameters were determined. The observation of SiC in the circumstellar shell of IRC +10216 suggests that metal carbides such as FeC may be present as well.

The millimeter-wave spectrum of FeO in its X5Δi state (v = 0): a study of all five spin components

Abstract New millimeter/sub-millimeter pure rotational spectroscopy has been carried out for the FeO radical (X5Δi). The molecule was produced by the reaction of N2O with iron vapor, generated using a Broida-type oven. In addition to verifying previous measurements on FeO in the lower spin-orbit components, transitions originating in the Ω = 0 and 1 ladders have been recorded, for which lambda-type doubling was resolved. Spectra of the 54FeO isotopomer were also measured. The data set was analyzed successfully with a 5Δ Hamiltonian, demonstrating that highly perturbed, complicated electronic ground states can be modeled with effective rotational parameters.

The millimeter and sub-millimeter spectrum of the BaOH radical

The pure rotational spectrum of the X2Σ+ ground electronic states of the BaOH and BaOD radicals has been observed using millimeter/sub-millimeter direct absorption spectroscopy. The lesser abundant isotopically substituted species, 136BaOH and 137BaOH, have been detected as well. The radicals were created by reacting barium metal vapor, produced in a Broida-type oven, with either H2O2 or D2O2. The rotational and spin—rotation constants were determined for the molecules from a nonlinear leastsquares fit to the data, using a 2Σ Hamiltonian. Hyperfine constants were also derived for 137BaOH, the one species where hyperfine structure was resolved. These measurements confirm a linear structure for BaOh.

Millimeter-wave spectroscopy of FeF (X 6Δi): Rotational analysis and bonding study

The pure rotational spectrum of the FeF radical in its 6Δi ground electronic state has been recorded using millimeter/submillimeter direct absorption techniques. Transitions arising from all six spin-orbit components have been observed in the v=0, 1, and 2 vibrational levels of 56FeF, the main isotopic species, and also in the less abundant 54Fe isotopomer. Hyperfine splittings, arising from the 19F nuclear spin of I=1/2, were resolved in the majority of transitions recorded, and lambda-doubling interactions were observed in the Ω=3/2, 1/2, and −1/2 spin-orbit ladders. The complete data set has been analyzed using a 6Δ Hamiltonian, and rotational, spin-orbit, spin–spin, lambda-doubling, and hyperfine constants determined. This study has conclusively demonstrated that the ground electronic state of FeF is 6Δi. It also suggests that FeF has more covalent character to its bonding than alkaline earth or alkali metal counterparts.

A millimeter/sub-millimeter-wave spectroscopic study of the FeCl radical (X6Δi)

Pure rotational spectroscopy of the FeCl radical (X6Δi) has been carried out using millimeter/sub-millimeter direct absorption techniques. The species was created by the reaction of chlorine with iron vapor. All six spin-orbit components were observed in the majority of the twenty-one rotational transition recorded. Chlorine hyperfine structure was resolved in the Ω = 92 and 72 components, and lambda-type doubling observed in the Ω = 3212, and −12 ladders. The data were analyzed with a 6Δ Hamiltonian, and rotational, fine structure, lambda-doubling, and hyperfine parameters determined. The hyperfine and lambda-doubling interactions in FeCl appear to be different from those in the FeF radical.

Millimeter‐wave spectroscopy of MgF: Structure and bonding in alkaline–earth monofluoride radicals

The pure rotational spectrum of the MgF radical in its ground electronic state (X 2Σ+) has been recorded using millimeter/submillimeter direct absorption techniques. Transitions arising from the v=0, 1, 2, and 3 vibrational modes of the main magnesium isotopic species, 24MgF, have been observed. In addition, spectra of the isotopomers 26MgF and 25MgF in the natural abundances of magnesium have been detected. Rotational and fine structure constants have been determined for these species, as well as hyperfine parameters for the fluorine nucleus (I=1/2). For 25MgF, the hyperfine structure was also resolved arising from the magnesium nucleus, which has I=5/2, yielding the 25Mg hyperfine and quadrupole constants. Comparison of these hyperfine parameters with those of the heavier alkaline–earth monofluorides and the free 25Mg+ atom suggests that there is an increase in covalent bonding in MgF vs its heavier fluoride counterparts. This behavior is also apparent in the hybridization of the wave function of the un...

The millimeter-wave spectrum of the CaF radical (X(sup 2)Sigma(+))

The pure rotational spectrum of the CaF radical has been measured in the laboratory using millimeter/sub-mm direct absorption spectroscopy. Fourteen rotational transitions have been detected originating in the v = 0 mode of the species. Rotational lines of the vibrationally excited v = 1, 2, and 3 states have also been observed. Spin-rotation splittings, as well as hyperfine interactions arising from the nuclear spin of the fluorine atom, were resolved in the CaF spectra. Rotational, fine-structure, and in some cases, hyperfine parameters were determined for the various vibrational modes of the molecule from a nonlinear least-squares fit to the data, using a (sup 2)Sigma Hamiltonian, and are in agreement with past measurements. The newly measured rest frequencies for CaF, which are accurate to at least + or - 100 kHz, will enable astronomical searches to be conducted for the molecule in interstellar and circumstellar gas. Given the recent detection of AlF in IRC + 10216, metal fluoride species may be more abundant than previously thought.

MILLIMETER AND SUBMILLIMETER REST FREQUENCIES FOR THE MGF RADICAL

The pure rotational spectrum of the MgF radical in its ground X(sup 2) Sigma(+) electronic state has been observed in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Rotational transitions arising from the v = 0, 1, 2, and 3 vibrational modes of the main magnesium isotopic species, (24)MgF, have been recorded, as well as those arising from the v = 0 state of the Mg-25 and Mg-26 isotopomers. Rotational and fine-structure constants have been determined for these molecules, as well as hyperfine parameters for both the F-19 (I = 1/2) and Mg-25 (I = 5/2) nuclei. The rest frequencies presented here for MgF have an estimated accuracy of +/- 200 kHz, and will enable astronomical searches to be carried out for this fluoride radical. Magnesium fluoride may be present in the late-type carbon star IRC +10216, where AlF appears to be abundant.

Metal‐containing molecules in the laboratory and in space

Laboratory and observational studies of various metal‐containing compounds are presented. The millimeter and sub‐mm spectra of several hydroxide, hydride, fluoride and cyanide metal free radicals have been measured at high resolution using direct absorption spectroscopy. The species have subsequently been searched for in the interstellar medium.