Iron monocarbide has been investigated between 12 000 and 18 100 cm Ϫ1 in a supersonic expansion by resonant two-photon ionization spectroscopy. Six new electronic states have been identified for which origins relative to the ground state have been determined. Three of these possess ⍀Јϭ3, one possesses ⍀Јϭ4, and two possess ⍀Јϭ2. The ⍀Јϭ3 state with an origin near 13 168 cm Ϫ1 is likely a 3 ⌬ 3 state and has been assigned as the analog of the ͓14.0͔ 2 ⌺ ϩ ←X 2 ⌺ ϩ charge transfer transition in CoC. The ⍀Јϭ4 state is most likely a 3 ⌽ 4 state. Additionally, seven bands with ⍀Јϭ2 have been observed that have proven impossible to systematically group by electronic state. Because every transition rotationally resolved in this study possesses a lower state with ⍀ϭ3, the ground state has been confirmed as arising from an ⍀ϭ3 state that is most likely the ⍀ϭ3 spin orbit component of a 3 ⌬ i term derived from a 1␦ 3 9 1 configuration. The ionization energy ͑IE͒ of FeC has been determined as 7.74Ϯ0.09 eV by varying the wavelength of the ionization photon. When combined with the known IE of Fe and the bond energy of FeC ϩ , the bond energy of FeC is calculated to be 3.9Ϯ0.3 eV. Presentation of the results is accompanied by an analysis of the bonding in FeC from a molecular orbital standpoint.

The rotational spectrum of jet-cooled hafnium dioxide obtained by laser ablation of a solid ceramic rod has been investigated by Fourier-transform microwave spectroscopy in the 8 to 28 GHz frequency range. Rotational transitions within the ground and several excited vibrational states of the lowest vibrational mode of the molecule have been assigned. The resulting spectra have been fit, yielding rotational parameters for the five most abundant isotopomers of HfO2. Centrifugal distortion effects are noticeable even for the lowest-J transitions. Very large quadrupole coupling effects for the isotopomers with nuclear quadrupole moments (179Hf (I=9/2) and Hf177 (I=7/2)) have been accounted for using the diagonal elements of the nuclear quadrupole coupling tensor. A ground-state effective C2v geometry has been obtained for HfO2, yielding ro(Hf–O)=1.7764(4) Å and ∠(O–Hf–O)=107.51(1)°. The electric dipole moment has been determined for HfO2180 from Stark-effect measurements, giving μ=26.42(3)×10-30C⋅m [7.92(1) D]. Ab initio calculations using density functional theory and relativistic core potentials are in satisfactory agreement with the experimental results. Finally, in the course of this investigation, the rotational spectrum of the diatomic molecule, HfO, has also been reexamined, and new results for vibrational satellites (up to v=18 in some cases) of the J=1←0 rotational transition are reported. A vibrational analysis using Le Roy’s form of the Dunham expansion has allowed the determination of atomic mass-dependent Born–Oppenheimer breakdown parameters for both atoms of HfO.

The pure rotational spectrum of the asymmetric top ZrO 2 has been collected using a Fourier transform microwave spectrometer that employed a laser ablation molecular beam source. Four rotational transitions for each of five Zr 16 O 2 isotopomers have been recorded. The rotational constants of the 90 Zr 16 O 2 isotope were determined to be Aϭ19 881.352 MHzϮ0.068 MHz, B ϭ7693.895 MHzϮ0.021 MHz, and Cϭ5533.111 MHzϮ0.036 MHz. The r 0 structure was determined to possess a Zr-O bond length of 1.7710 ÅϮ0.0007 Å, and an O-Zr-O bond angle of 108.11°Ϯ0.08°. The electric dipole moment has been measured for the 90 Zr 16 O 2 isotope and found to be b ϭ26.02ϫ10 Ϫ30 C•mϮ0.07ϫ10 Ϫ30 C•m ͓7.80 DebyeϮ0.02 Debye͔. The nuclear quadrupole hyperfine structure for the 91 Zr 16 O 2 isotope has also been recorded and analyzed, yielding aa ϭ115.94 MHzϮ0.16 MHz, bb ϭϪ37.55 MHzϮ0.33 MHz, and cc ϭϪ78.39 MHz Ϯ0.16 MHz. High-level density functional theory calculations yield a structure that agrees well with the values determined experimentally. Several new transitions assigned to Zr 16 O were also recorded in the course of this study, and these were analyzed to extract values of B e , ␣ e , and ␥ e for four isotopomers.

The first optical spectroscopic investigation of MoC has revealed a complicated vibronic spectrum consisting of about 35 bands between 17 700 and 24 000 cm−1. Analysis has shown the ground state to be the Ω=0+ spinorbit component of a Σ3− state that derives from a 10σ211σ25π42δ2 configuration. The X 3Σ0+− rotational constant for Mo9812C was determined to be B0=0.553 640±0.000 055 cm−1, giving r0=1.687 719±0.000 084 Å. Consideration of spin-uncoupling effects in the X 3Σ− state requires that this value be revised to r0=1.6760 Å, which represents our best estimate of the true Mo–C bond length. Spectroscopic constants were also extracted for six other major isotopic modifications of MoC in this mass resolved experiment. All rotationally resolved transitions were found to originate from the ground state and terminate in electronic states with Ω=1. An attempt is made to classify the observed transitions into band systems, to rationalize the complexity of the spectrum, and to understand the bonding from a molecular orbital point of view.

The conformational and structural properties of the inhalational anesthetic isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether) have been probed in a supersonic jet expansion using Fourier-transform microwave (FT-MW) spectroscopy. Two conformers of the isolated molecule were identified from the rotational spectrum of the parent and several 37 Cl and 13 C isotopologues detected in natural abundance. The two most stable structures of isoflurane are characterized by an anti carbon skeleton (t(C 1 -C 2 -O-C 3 ) = 137.8(11)1 or 167.4(19)1), differing in the trans (AT) or gauche (AG) orientation of the difluoromethyl group. The conformational abundances in the jet were estimated from relative intensity measurements as (AT)/(AG) E 3 : 1. The structural preferences of the molecule have been rationalized with supporting ab initio calculations and natural-bond-orbital (NBO) analysis, which suggest that the molecule is stabilized by hyperconjugative effects. The NBO analysis of donor-acceptor (LP -s*) interactions showed that these stereoelectronic effects decrease from the AT to AG conformations, so the conformational preferences can be accounted for in terms of the generalized anomeric effect.