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The pure rotational spectrum of HZnCN in its X 1Σ+ electronic state has been recorded using pulsed Fourier transform microwave (FTMW) techniques in the frequency range 7–39 GHz—the first spectroscopic study of this species in the gas phase. The FTMW spectrum of ZnCN(X 2Σ+) has been measured as well. A new FTMW spectrometer with an angled beam and simplified electronics, based on a cryopump, was employed for these experiments. The molecules were created in a dc discharge from a gas mixture of Zn(CH3)2 and cyanogen (1% D2 for the deuterated analogs), diluted with argon, that was expanded supersonically from a pulsed nozzle. Seven isotopologues of HZnCN arising from zinc, deuterium, and 13C substitutions were studied; for every species, between three and five rotational transitions were recorded, each consisting of numerous hyperfine components arising from nitrogen, and in certain cases, deuterium, and 67-zinc nuclear spins. Four transitions of ZnCN were measured. From these data, rotational, nuclear spin-rotation, and quadrupole coupling constants have been determined for HZnCN, as well as rotational, and magnetic and quadrupole hyperfine parameters for the ZnCN radical. The bond lengths determined for HZnCN are rH–Zn=1.495 Å, rZn–C=1.897 Å, and rC–N=1.146 Å, while those for ZnCN are rZn–C=1.950 Å and rC–N=1.142 Å. The zinc-carbon bond length thus shortens with the addition of the H atom. The nitrogen quadrupole coupling constant eqQ was found to be virtually identical in both cyanide species (-5.089 and -4.931 MHz), suggesting that the electric field gradient across the N nucleus is not influenced by the H atom. The quadrupole constant for the 67Zn nucleus in H67ZnCN is unusually large relative to that in 67ZnF (-104.578 versus -60 MHz), evidence that the bonding in the cyanide has more covalent character than in the fluoride. This study additionally suggests that hydrides of other metal cyanide species are likely candidates for high resolution spectroscopic investigations. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of HZnCN in its X 1Σ+ electronic state has been recorded using pulsed Fourier transform microwave (FTMW) techniques in the frequency range 7–39 GHz—the first spectroscopic study of this species in the gas phase. The FTMW spectrum of ZnCN(X 2Σ+) has been measured as well. A new FTMW spectrometer with an angled beam and simplified electronics, based on a cryopump, was employed for these experiments. The molecules were created in a dc discharge from a gas mixture of Zn(CH3)2 and cyanogen (1% D2 for the deuterated analogs), diluted with argon, that was expanded supersonically from a pulsed nozzle. Seven isotopologues of HZnCN arising from zinc, deuterium, and 13C substitutions were studied; for every species, between three and five rotational transitions were recorded, each consisting of numerous hyperfine components arising from nitrogen, and in certain cases, deuterium, and 67-zinc nuclear spins. Four transitions of ZnCN were measured. From these data, rotational, nuclear spin-rotation, and quadrupole coupling constants have been determined for HZnCN, as well as rotational, and magnetic and quadrupole hyperfine parameters for the ZnCN radical. The bond lengths determined for HZnCN are rH–Zn=1.495 Å, rZn–C=1.897 Å, and rC–N=1.146 Å, while those for ZnCN are rZn–C=1.950 Å and rC–N=1.142 Å. The zinc-carbon bond length thus shortens with the addition of the H atom. The nitrogen quadrupole coupling constant eqQ was found to be virtually identical in both cyanide species (-5.089 and -4.931 MHz), suggesting that the electric field gradient across the N nucleus is not influenced by the H atom. The quadrupole constant for the 67Zn nucleus in H67ZnCN is unusually large relative to that in 67ZnF (-104.578 versus -60 MHz), evidence that the bonding in the cyanide has more covalent character than in the fluoride. This study additionally suggests that hydrides of other metal cyanide species are likely candidates for high resolution spectroscopic investigations. [ABSTRACT FROM AUTHOR]

Millimeter wave rotational spectroscopy and ab initio calculations are used to explore the potential energy surface of LiOH and LiOD with particular emphasis on the bending states and bending potential. New measurements extend the observed rotational lines to J=7←6 for LiOH and J=8←7 for LiOD for all bending vibrational states up to (0330). Rotation-vibration energy levels, geometric expectation values, and dipole moments are calculated using extensive high-level ab initio three-dimensional potential energy and dipole moment surfaces. Agreement between calculation and experiment is superb, with predicted Bv values typically within 0.3%, D values within 0.2%, ql values within 0.7%, and dipole moments within 0.9% of experiment. Shifts in Bv values with vibration and isotopic substitution are also well predicted. A combined theoretical and experimental structural analysis establishes the linear equilibrium structure with re(Li–O)=1.5776(4) Å and re(O–H)=0.949(2) Å. Predicted fundamental vibrational frequencies are v1=923.2, v2=318.3, and v3=3829.8 cm-1 for LiOH and v1=912.9, v2=245.8, and v3=2824.2 cm-1 for LiOD. The molecule is extremely nonrigid with respect to angular deformation; the calculated deviation from linearity for the vibrationally averaged structure is 19.0° in the (000) state and 41.9° in the (0330) state. The calculation not only predicts, in agreement with previous work [P. R. Bunker, P. Jensen, A. Karpfen, and H. Lischka, J. Mol. Spectrosc. 135, 89 (1989)], a change from a linear to a bent minimum energy configuration at elongated Li–O distances, but also a similar change from linear to bent at elongated O–H distances. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of the SrSH radical in its ground electronic (&Xtilde; ²A′) and vibrational states has been measured using millimeter/submillimeter-wave direct absorption techniques. This work is the first observation of SrSH with rotational resolution. The spectrum of its deuterium isotopomer SrSD and SrS (X ¹∑[sup +)] has been recorded as well. These species were created by the reaction of strontium vapor and H[sub 2]S, in the presence of a dc discharge. SrS was also made with CS[sub 2]. For SrSH and SrSD, eight rotational transitions were recorded, respectively, for which asymmetry components up to K[sub a] = 8 were measured; fine structure was also resolved in each component. Thirteen transitions of SrS in each of its υ = 0, 1, and 2 states have additionally been observed. These data have been analyzed and spectroscopic parameters determined for all three species, including spin-rotation terms for the strontium hydrosulfides. From an r[sub 0] structure calculation, the bond angle in SrSH was determined to be 91.48(3)°, very close to that of H[sub 2]S and CaSH. This geometry indicates that SrSH is a covalently bonded molecule, as opposed to linear (and ionic) SrOH. The Sr-S bond length in SrSH was also found to be greater than that of SrS (r[sub Sr-S] = 2.705 Å versus 2.441 Å), indicating a change in bond order. In addition, the spin-rotation interaction in SrSH and SrSD includes a small contribution from the off-diagonal term, (ε[sub ab] + ε[sub ba])/2, resulting from the crossing of energy levels with ΔJ = 0, ΔK[sub a] = ± 1. Second-order spin-orbit coupling appears to make a significant contribution to the spin-rotation splitting, as well, which must arise from mixing of the à ²A&′ and &Btilde; ²A″ excited states. © 2001 American Institute of Physics. [DOI: 10.1063/1.1419060]. [ABSTRACT FROM AUTHOR]

Reports that pure rotational spectra of the MgOH and MgOD radicals have been recorded in the v[sub 2] bending vibration of their X[sup 2]Sigma[sup +] ground electronic states using direct absorption spectroscopy. Use of a linear model for the Hamiltonian in analysis of the data.

Reports that a second low-lying cyclic isomer of SiC[sub 3] has been detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. Isomer's nature as a planar rhomboid with a transannular bond C[sub 2v] symmetry; Transannular bond between Si and C.

Investigates the HC4N molecular system, which is calculated to possess several low-lying, highly polar carbene isomers. High-level coupled cluster calculation; Rotational spectrum of the bent HC4N singlet carbene; Use of Fourier transform microwave spectroscopy; Leading centrifugal distortion constants; Nitrogen hyperfine coupling constants; Large inertial defect.

Studies the rotational spectrum of rhomboidal silicon tricarbide, the long-predicted planar ring with a transannular bond. Centimeter and millimeter-wave measurements; Fourier transform microwave (FTM) spectrometer; Spectroscopic analysis.

Investigates a molecule with the elemental formula of silicon carbide, a closed-shell singlet electronic ground states, and a planar rhomboidal geometry that consists of atoms in the shape of a distorted four-membered ring with a transannular carbon-carbon bond. Identification of the identity and precise determination of the length of rhomboidal silicon carbon through isotopic substitution.

Pure rotational spectra of CaOD and MgOD have been recorded in the range 200–390 GHz using millimeter/sub-mm direct absorption spectroscopy. Transitions arising from the (000), (010), (020), and (100) modes have been measured for the 2Σ+ ground electronic states of these free radicals. The data were analyzed successfully using a linear 2Σ+ model for CaOD; for MgOD, only the (000) and (010) states could be fit with this Hamiltonian. Moreover, the (010) data required the addition of a substantial pΠ term to account for contamination of excited 2Π electronic states. For both species, the α2 vibration–rotation term was found to be negative, in contrast to MgOH and CaOH, suggesting a less anharmonic contribution to the bending potential in CaOD and MgOD. These measurements also indicate a shorter O–H bond in MgOH than the other alkaline earth hydroxide radicals, which likely results because this species is quasilinear. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The structures of two linear silicon carbides, SiC[sub 4] and SiC[sub 6], have been determined by a combination of isotopic substitution and large-scale coupled-cluster ab initio calculations, following detection of all of the singly substituted isotopic species in a supersonic molecular beam with a Fourier transform microwave spectrometer. Rotational constants obtained by least-squares fitting transition frequencies were used to derive experimental structures; except for those nearest the center of mass, individual bond lengths for both chains have an error of less than 0.008 Å. Accurate equilibrium structures were derived by converting the experimental rotational constants to equilibrium constants using the vibration-rotation coupling constants from coupled-cluster calculations, including connected triple substitutions. Equilibrium dipole moments and harmonic vibrational frequencies were also calculated for both chains. On the basis of the calculated vibration-rotation and l-type doubling constants, weak rotational satellites from a low-lying vibrational state of SiC[sub 4] were assigned to v[sub 6], a bending mode calculated to lie about 205 cm-1 above the ground state. A recommended ab initio equilibrium structure for SiC[sub 8] has also been established. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Three new silicon–carbon chains, SiC[sub 4]H, SiC[sub 5]H, and SiC[sub 6]H, have been detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. A detailed spectroscopic characterization of these and the previously described chains SiCCH, SiCN, and SiNC is given here. All six radicals are linear chains with [sup 2]Π electronic ground states and all have resolvable hyperfine structure in their lower rotational transitions; all except SiC[sub 5]H have resolved lambda-type doubling. Because transitions of SiCCH, SiCN, and SiNC were also detected by millimeter-wave absorption spectroscopy in both spin components, for these the rotational, centrifugal distortion, and fine structure and hyperfine coupling constants were determined to high precision using the standard Hamiltonian for a molecule in a [sup 2]Π state. For SiC[sub 4]H, SiC[sub 5]H, and SiC[sub 6]H, at least seven transitions in the lowest-energy fine structure component were measured between 7 and 30 GHz, and, at most, five spectroscopic constants were required to reproduce their spectra to a few parts in 10[sup 7]. The hyperfine coupling constants of the SiC[sub n]H radicals are fairly close to those of isovalent C[sub n+1]H, indicating that the chemical bonding may be similar. The missing radical in the present sequence, SiC[sub 3]H, may soon be found along with cyclic isomers of SiCCH and SiC[sub 4]H. If SiC[sub 5]H possesses strong electronic transitions in the visible like isovalent C[sub 6]H, its spectrum should be detectable by long path optical spectroscopy. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The rotational spectra of the HCCCNH[sup +], NCCNH[sup +], and CH[sub 3]CNH[sup +] ions have been observed in a supersonic molecular beam by Fourier transform microwave (FTM) spectroscopy. The rotational and centrifugal distortion constants were determined for all three, and the nitrogen quadrupole hyperfine coupling constants for HCCCNH[sup +] and NCCNH[sup +]. From the respective Doppler shifts, it is found that the velocities of the ions are 3% larger than those of the parent unprotonated molecules, and the linewidths are greater by about 50%. The concentration of the ions near the nozzle is approximately 10[sup 11] cm[sup -3], which is sufficiently high to be detectable in the visible and the IR by present laser techniques. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]