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

Pure rotational spectroscopy of the FeCl radical (X⁶Δ_i) 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 = 9/2 and 7/2 components, and lambda-type doubling observed in the Ω = 3/21/2, and −1/2 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.     

Perturbations in the pure rotational spectrum of CoCl (X 3 Phi i): a submillimeter study

The millimeter/submillimeter-wave spectrum of the CoCl radical (X (3)Phi(i)) has been recorded using direct absorption techniques in the frequency range 340-510 GHz. This work is the first pure rotational study of this molecule. The radical was created by the reaction of Cl(2) with cobalt vapor. Rotational transitions arising from the Omega=4, 3, and 2 spin-orbit components of Co(35)Cl have been measured, all of which exhibit hyperfine splittings due to the (59)Co nucleus (I=7/2). Transitions arising from the Co(37)Cl species were also recorded, as well as those originating in the v=1, 2, 3, and 4 vibrational states of both isotopomers. The spin-orbit pattern exhibited by the molecule is unusual, with the Omega=3 component significantly shifted relative to the other spin components. In addition, the regular octet hyperfine splittings become distorted above a certain J value for the Omega=3 transitions only. These effects suggest that the molecule is highly perturbed in its ground state, most likely a result of second-order spin-orbit mixing with a nearby isoconfigurational (1)Phi(3) state. The complete data set for Co(35)Cl and Co(37)Cl were fit successfully with a case (a) Hamiltonian but required a large negative spin-spin constant of lambda=-7196 GHz and higher order centrifugal distortion corrections to the rotational, spin-orbit, spin-spin, and hyperfine terms. The value of the spin-spin constant suggests that the Omega=3 component is shifted to higher energy and lies near the Omega=2 sublevel. The hyperfine parameters are consistent with a delta(3)pi(3) electron configuration and indicate that CoCl is more covalent than CoF.     

Rapid crack growth in a thermoelastic solid under mixed-mode thermomechanical loading

A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed.     

Millimeter-wave rotational spectroscopy of FeCN (X 4Δi) and FeNC (X 6Δi): determining the lowest energy isomer

The pure rotational spectrum of FeCN has been recorded in the frequency range 140-500 GHz using millimeter/sub-millimeter direct absorption techniques. The species was created in an ac discharge of Fe(CO)(5) and cyanogen. Spectra of the (13)C, (54)Fe, and (57)Fe isotopologues were also measured, confirming the linear cyanide structure of this free radical. Lines originating from several Renner-Teller components in the ν(2) bending mode were also observed. Based on the observed spin-orbit pattern, the ground state of FeCN is (4)Δ(i), with small lambda-doubling splittings apparent in the Ω = 5/2, 3/2, and 1/2 components. In addition, a much weaker spectrum of the lowest spin-orbit component of FeNC, Ω = 9/2, was recorded; these data are consistent with the rotational parameters of previous optical studies. The data for FeCN were fit with a Hund's case (a) Hamiltonian and rotational, spin-orbit, spin-spin, and lambda-doubling parameters were determined. Rotational constants were also established from a case (c) analysis for the other isotopologues, excited vibronic states, and for FeNC. The r(0) bond lengths of FeCN were determined to be r(Fe-C) = 1.924 ? and r(C-N) = 1.157 ?, in agreement with theoretical predictions for the (4)Δ(i) state. These measurements indicate that FeCN is the lower energy isomer and is more stable than FeNC by ~1.9 kcal/mol.     

The pure rotational spectrum of HPS (X̃1A'): chemical bonding in second-row elements

The pure rotational spectrum of HPS, as well as its (34)S and D isotopologues, has been recorded at microwave, millimeter, and submillimeter wavelengths, the first observation of this molecule in the gas phase. The data were obtained using a combination of millimeter direct absorption, Fourier transform microwave (FTMW), and microwave-microwave double-resonance techniques, which cover the total frequency range from 15 to 419 GHz. Quantum chemical calculations at the B3LYP and CCSD(T) levels were also performed to aid in spectral identification. HPS was created in the direct absorption experiment from a mixture of elemental phosphorus, H(2)S, and Ar carrier gas; DPS was produced by adding D(2). In the FTMW study, these species were generated in a pulsed discharge nozzle from PH(3) and H(2)S or D(2)S, diluted in neon. The spectra recorded for HPS and its isotopologues exhibit clear asymmetric top patterns indicating bent structures; phosphorus hyperfine splittings were also observed in HPS, but not DPS. Analysis of the data yielded rotation, centrifugal distortion, and phosphorus nuclear spin-rotation parameters for the individual species. The r(m) ((1)) structure for HPS, calculated from the rotational constants, is r(H-P) = 1.438(1) A?, r(P-S) = 1.9320(1) A?, and θ(H-P-S) = 101.85(9)°. Empirically correcting for zero-point vibrational effects yields the geometry r(e)(H-P) = 1.4321(2) A?, r(e)(P-S) = 1.9287(1) A?, and θ(e)(H-P-S) = 101.78(1)°, in close agreement with the r(m) ((1)) structure. A small inertial defect was found for HPS indicating a relatively rigid molecule. Based on these data, the bonding in this species is best represented as H-P=S, similar to the first-row analog HNO, as well as HNS and HPO. Therefore, substitution of phosphorus and sulfur for nitrogen and oxygen does not result in a dramatic structural change.     

The pure rotational spectrum of ZnS (XΣ)

The pure rotational spectrum of ZnS (X¹Σ⁺) has been measured using direct-absorption millimeter/sub-millimeter techniques in the frequency range 372–471 GHz. This study is the first spectroscopic investigation of this molecule. Spectra originating in four zinc isotopologues (⁶⁴ZnS, ⁶⁶ZnS, ⁶⁸ZnS, and ⁶⁷ZnS) were recorded in natural abundance in the ground vibrational state, and data from the v = 1 state were also measured for the two most abundant zinc species. Spectroscopic constants have been subsequently determined, and equilibrium parameters have been estimated. The equilibrium bond length was calculated to be r_e  2.0464 Å, which agrees well with theoretical predictions. In contrast, the dissociation energy of D_E  3.12 eV calculated for ZnS, assuming a Morse potential, was significantly higher than past experimental and theoretical estimates, suggesting diabatic interaction with other potentials that lower the effective dissociation energy. Although ZnS is isovalent with ZnO, there appear to be subtle differences in bonding between the two species, as suggested by their respective force constants and bond length trends in the 3d series.     

Completing the 3d metal fluoride series: the pure rotational spectrum of ZnF (X2Sigma+)

The pure rotational spectrum of the ZnF radical has been recorded in the range of 176-527 GHz using millimeter/submillimeter direct absorption techniques. This study is the first gas-phase spectroscopic investigation of this species. Between 5 and 11 transitions were measured for each of five isotopologues of this radical (64ZnF, 66ZnF, 67ZnF, 68ZnF, and 70ZnF) in the ground and several excited vibrational (v=1, 2, and 3) states. Each transition consists of spin-rotation doublets with a splitting of approximately 150 MHz, indicating that the electronic ground state of ZnF is 2Sigma+, as predicted by theory. Fluorine hyperfine splitting was observed in three isotopologues (64ZnF, 66ZnF, and 67ZnF), and hyperfine structure from the zinc-67 nucleus (I=52) was additionally resolved in 67ZnF. Rotational, fine structure, and 19F and 67Zn hyperfine constants were determined for ZnF, as well as equilibrium parameters. The bond length of the main isotopologue 64ZnF was calculated to be re=1.7677 A. Evaluation of the hyperfine constants indicates that the sigma orbital containing the unpaired electron is approximately 80% 4s(Zn) in character with approximately 10% contributions from each of the 2p(F) and 4p(Zn) orbitals. These results imply that ZnF is somewhat less ionic than CaF, as suggested by theory.     

Structures of Solvent-Free,Monomeric LiCCH,NaCCH, and KCCH

The simplest alkali metal acetylides MCCH were made in the gas phase for the first time (see drawing), and their bond lengths were determined by millimeter/submillimeter spectroscopy of their isotopomers. The M−C bond lengths r_CM are the shortest known for organoalkali metal compounds. In the case of LiCCH, the experimentally determined Li−C distance of 1.888 Å has an estimated accuracy of ±0.0005 Å, which should allow a rigorous test of theoretical methods.