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The microwave spectrum for o-benzyne was obtained by passing a dilute (<1%) mixture of benzene in neon through a pulsed-DC discharge nozzle source into a pulsed-beam, Fourier transform spectrometer. Rotational transitions were measured for the normal isotopomer, the two unique single-D isotopomers, and the [sup 13]C isotopomer and one of the [sup 13]C isotopomers. Benzynes have been known as reactive intermediates in organic reactions for many years, and have recently been implicated in gasoline combustion reactions and antitumor activity of enediynes. Twenty-seven b-type transitions for the normal isotopomer were fit to obtain A=6989.7292(6), B=5706.8062(6), and C=3140.3708(4) MHz, and five centrifugal distortion constants. The inertial defect is Δ=0.069 4 amu Å[sup 2], consistent with a planar structure. Hyperfine structure for the D[sub 1] (closest to the C=C bond) and D[sub 2] (furthest from the C=C bond), was analyzed to obtain deuterium quadrupole coupling strengths eQq[sub aa](D[sub 1])=185(3) kHz, eQq[sub bb](D[sub 1])=-85(2) kHz, eQq[sub aa](D[sub 2])=5(13), and eQq[sub bb](D[sub 2])=86(13) kHz. The C–D, bond axis quadrupole coupling strengths are compared with values for benzene. Spectra for the [sup 13]C[sub 6] and one of the [sup 13]C[sub 1] isotopomers were analyzed to obtain rotational constants. Kraitchman analysis and least-squares fitting provided nearly all of the structural parameters. The preliminary structural analysis yields an acetylenic C≡C bond length of 1.24 Å, in agreement with a recent NMR value. Density functional theory (DFT) calculations were used to obtain structural parameters, and values obtained are in very good agreement with present experimental results. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Microwave rotational spectra for six isotopomers of HCo(CO)4 were measured using a Flygare–Balle type spectrometer. Transitions were measured in the 4–10 GHz range. The data were analyzed to obtain rotational constants, 59Co quadrupole coupling strengths, distortion constants and spin–rotation interaction strengths. The common isotopomer is clearly a symmetric top, with C3v symmetry. For the common isotopomer B=1131.7212(9) MHz and eQq(59Co)=116.62(3) MHz. The rotational constants were used to determine the complete, three-dimensional structure of this complex. The measured H–Co bond length of 1.52(2) Å is significantly shorter than the previous value from electron diffraction work. Other structural parameters for this complex are reported and discussed. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Microwave spectra for four isotopomers of benzene chromium tricarbonyl were measured in the 4–17 GHz range using a Flygare–Balle type pulsed beam spectrometer. Rotational constants obtained are B(52Cr)=732.8886(6) MHz and B(53Cr)=732.8966(3) MHz. Asymmetric top spectra were observed for a single 13C substitution on the benzene ring giving B(13C–bz)=729.9606(3) and C(13C–bz)=727.9024(2) MHz. For a single 13C substitution on one of the carbonyl carbons B(13CO)=731.9036(8) and C(13CO)=729.1657(8) MHz. Since no effects of possible internal rotation were observed on the 13C asymmetric top spectra, we can place a lower limit on the V6 potential for internal rotation of V6>=4.0 THz (=1.6 kJ/mole). The centrifugal distortion constants are small, DJ=0.05 kHz and DJK=-0.05 kHz, indicating a fairly rigid structure. The 53Cr quadrupole coupling strength is low, eqQ(53Cr)=-12.11(1) MHz, indicating a near octahedral charge distribution around the Cr atom. Structural parameters obtained are the center of the benzene chromium distance r(Cr–bz)=1.67(2) Å, the chromium–carbonyl bond length r(Cr–CO)=1.86(1) Å and the OC–Cr–CO interbond angle α=88(1)°. [ABSTRACT FROM AUTHOR]

J=2→3, 3→4, 4→5, and 5→6 transitions in the oblate symmetric top molecule cobalt tricarbonyl nitrosyl were measured using a Flygare–Balle type pulsed beam microwave spectrometer. K=0 and K=3 transitions were observed for J=3→4 and 4→5. Hyperfine structure due to 59Co and 14N nuclear quadrupole coupling interactions was well resolved. The measured quadrupole coupling strengths are eQqcc (59Co)=35.14(30) MHz and eQqcc (14N)=-1.59(10). Measured rotation and distortion constants are B0=1042.1590(4) MHz and Dj =0.17(8) kHz. The measured B value is 4% smaller than the B value calculated from electron diffraction data. Spin–rotation and a quadrupole distortion term were also obtained for 59Co. [ABSTRACT FROM AUTHOR]

A total of 60 a- and b-dipole rotational transitions were measured in the 4–18 GHz range for the NNO–HCN, 15NNO–HCN, and NNO–DCN bimolecular complexes using a pulsed-beam, Fourier transform microwave spectrometer. Spectroscopic constants (A-DK), B, C, DJ, DJK, eQqaa (N of HCN), and eQqbb (N of HCN) were obtained by fitting the observed transition frequencies with a first-order quadrupole coupling interaction Hamiltonian. The structure of the complex appears to be planar with NNO and NCH nearly parallel. It can be described with the distance Rcm between the center-of-masses of the monomer subunits, the angle θ between HCN and Rcm, and the angle [lowercase_phi_synonym] between N2O and Rcm. A least-squares fit to the nine rotational constants to obtain the structure parameters Rcm, θ, and [lowercase_phi_synonym], produced three local minimia for bent structures with standard deviations of <25 MHz. A Kraitchman analysis was used to determine magnitudes of principal axes coordinates for the N of HCN, and the terminal N of NNO. The best nonlinear least-squares fit result (structure I, lowest standard deviation of the fit =7.2 MHz) produced the best match to the coordinates from the Kraitchman analysis. The spectroscopic constants B, C, and eQqaa were used in a second structural analysis to determine values for Rcm, θ, and [lowercase_phi_synonym]. These results were compared with the above coordinates. The best least-squares fit structure parameters for the vibrationally averaged structure are Rcm =3.253(4) Å, θ=89.1(5.4)°, and [lowercase_phi_synonym] =76.4(0.4)°. Comparisons are made with other similar weakly bound complexes. [ABSTRACT FROM AUTHOR]

Microwave measurements of rotational transitions for the linear ONN–DF and bent NNO–DF complexes were made using a pulsed-beam, Fourier transform spectrometer. For ONN–DF, B=1808.959(2) MHz and DJ=2.79(6) kHz. Structure parameters are obtained and compared with ONN–HF parameters. For the bent NNO–DF isomer, seven new transitions and previous data were fit to obtain (A+ΔK)=25 988.4(3) MHz, B=2701.1(2) MHz, C=2422.3(2) MHz, ΔJ=0.052(3) MHz, ΔJK=-2.57(1) MHz, δJ=0.010(5) MHz, and δK=0.24(10) MHz. The centrifugal distortion constants for NNO–DF are used to obtain force field parameters fRR and fΘΘ describing motion of the DF center of mass relative to the NNO center of mass. The excellent agreement between these parameters and previous data on NNO–HF supports the simplified model used to describe the centrifugal distortion of this complex. [ABSTRACT FROM AUTHOR]

Microwave spectra for the HI–HF, HI–DF, DI–HF, and DI–DF complexes were measured using a pulsed-beam, Fourier-transform microwave spectrometer. Rotational transitional transitions were measured over the 4–18 GHz range to an accuracy of 5 kHz. The spectroscopic constants obtained by fitting the observed transitions for the series HI–HF, HI–DF, DI–HF, and DI–DF are, respectively: (B+C)/2=2220.7482(8), 2173.236(2), 2209.623(4), and 2162.884(6) MHz; eQq(I)=687.01(2), 693.63(5), 725.96(4), and 727.8(1) MHz; ΔeQq(I)=-42(2), -50(6), -210(14), and -141(25) kHz; DJ =8.86(3), 8.25(6), 8.1(6), and 8.6(5) kHz. This complex has an interesting triangular structure with the H–I and H–F bonds making an acute angle of 70.1 (2.8)°. The iodine atom is coaxial with HF with a heavy atom separation R0(I–F)=3.660(8) Å. Hyperfine structure due to deuterium quadrupole coupling and H–F spin–spin interactions was resolved and measured. [ABSTRACT FROM AUTHOR]

Microwave measurements were made on the rotational spectrum of 2-sulpholene using a modified Flygare–Balle pulsed beam Fourier transform spectrometer. Analysis and calculations provided information on the large amplitude ring puckering vibration of this system. Twelve and six rotational transitions were measured for the v=0 and v=1 states of the ring puckering vibration, respectively. The transitions for each vibrational state were fitted to a Watson’s A reduced Hamiltonian including terms for quartic distortion yielding for v=0 the values B=2125.96(6), C=1983.28(8), ΔJK=0.664(4), ΔK=-0.34(4) MHz, and for v=1 the values A=3995(26), B=2128.3(1), C=1984.6(1), ΔJK=-0.8(1), ΔK=-32(6) MHz. Subsequently, ab initio calculations were performed at the self-consistent-field (SCF)/3-21G*, MP2/6-31G*, and MP4/6-31G* levels of theory to determine the barrier to inversion. The MP4/6-31G* barrier was ΔE=116 cm-1, and can be considered to be the most accurate barrier value calculated in this study. An ab initio potential energy curve was calculated at the SCF/3-21G* level in terms of a single parameter (ω) describing the large amplitude motion of the ring puckering. Vibration-coordinate dependence of the effective reduced mass associated with this large amplitude motion and the resultant kinetic energy expression was determined. The solutions of a one-dimensional Schrödinger equation solved within this double well potential yield a separation between the v=0 and v=1 large amplitude motion vibrational states of 8 cm-1 when the effective reduced mass was assumed constant, and a separation of 9 cm-1 when the effective reduced mass was expressed as a function of the ω coordinate. The v=0 and v=1 eigenfunctions for the SCF ring puckering potential were found to give vibrationally averaged rotational constants in good agreement with those obtained from the microwave spectrum. [ABSTRACT FROM AUTHOR]

Microwave measurements of rotational transitions in cyclopentadienyl manganese tricarbonyl were made using a Flygare–Balle type pulsed beam Fourier transform microwave spectrometer operating in the 4–14 GHz range. Ninety-six hyperfine transitions were assigned for this prolate symmetric top for the rotational transitions J=2→3, 3→4, 4→5, 5→6, and 6→7. Molecular constants obtained from the analysis of the spectrum are B=828.0333(6) MHz, DJ=0.088(9) kHz, DJK=-0.04(3) kHz, eQqaa(Mn)=68.00(4) MHz, Cbb(Mn)=-5.5(8) kHz. The distortion parameter DJ for CpMn(CO)3 is compared to other DJ values for similar type transition metal complexes. [ABSTRACT FROM AUTHOR]

Pulsed-beam Fourier transform microwave spectroscopy was used to measure a and b dipole transitions for the N2O–H35Cl, N2O–H37Cl, N2O–D35Cl, and 15NNO–H35Cl van der Waals complexes. The observed transition frequencies were fit to determine the spectroscopic constants A–DK, B, C, DJ, DJK, eQqaa(Cl), and eQqbb(Cl). The structure of the complex appears to be a planar asymmetric top with a centers-of-mass separation Rc.m. ≊ 3.51 Å. The angle θ between Rc.m. and the HCl axis is approximately 110°. The angle [lowercase_phi_synonym] between the N2O axis and Rc.m. is approximately 77°. The structure was fit using a weighted least squares fit to B and C isotopic rotational constants with Rc.m., θ, and [lowercase_phi_synonym] as the adjustable parameters, and this procedure yielded three local minima with standard deviations less than 5 MHz. Principal axis coordinates for the Cl, H, and terminal N atoms in the complex were determined with single isotopic Kraitchman analysis to aid in the selection of the ‘‘best’’ structure. In a second structural analysis Rc.m. θ, and [lowercase_phi_synonym] values were determined from the spectroscopic constants B, C, and eQqaa(Cl). The ‘‘best fit’’ structure parameters for N2O–HCl are Rc.m. =3.512(2) Å, θ =110(9)°, and [lowercase_phi_synonym] = 77(2)°. Ab initio calculations of N2O–HCl structures using GAUSSIAN86 with MP2 yielded three energetically stable equilibrium conformations. One of the bound structures is very similar to the present experimental vibrationally averaged structure. [ABSTRACT FROM AUTHOR]

Seventy-nine new microwave transitions for 35ClF3 and 37ClF3 in the 6–18 GHz range were measured using a Flygare–Balle-type spectrometer. Rotational transition frequencies were used to obtain ‘‘effective’’ structure parameters for the ground vibrational state zCl–F (along C2 axis)=1.5985(4) Å, rCl–F =1.700 73(5) Å and ΘF–Cl–F =87.48(4)°. Analysis of hyperfine structure due to chlorine quadrupole coupling and observed transition frequencies yield the following molecular parameters for 35ClF3: A=13 748.25(1) MHz, B=4611.719(2) MHz, C=3448.629(3) MHz, eQqaa=82.03(3) MHz, and eQqbb=65.35(2) MHz. Molecular parameters obtained for 37ClF3 are: A=13 653.54(1) MHz, B=4611.866(2) MHz, C=3442.719(4) MHz, eQqaa=64.66(4) MHz, and eQqbb=51.53(3) MHz. [ABSTRACT FROM AUTHOR]

The rotational spectra of H2S·CO2 and two deuterated forms have been observed using a pulsed-beam Fourier-transform microwave spectrometer. For each of the three complexes we assign a-type and c-type transitions which are split into a ‘‘weak’’ and a ‘‘strong’’ intensity component. The analysis based on that previously used for the (H2O)2 complex and modified for application to H2S·CO2, allowed us to assign internal rotation, inversion tunneling states of the H2S and CO2 units in the complex. The following rotational constants were determined for the ground tunneling state of each species: for H2S·CO2, A=11 048.0(26) MHz, B=2147.786(4) MHz, and C=1806.468(4) MHz; for HDS·CO2, A=10 769(35) MHz, B=2107.26(24) MHz, and C=1775.83(24) MHz; and for D2S·CO2, A=10 356.2(28) MHz, B=2065.376(8) MHz, and C=1746.122(8) MHz. The electric dipole moments were determined for the H2S·CO2 and D2S·CO2 species, resulting in the values μa=0.410(14) D and μc=0.822(10) D for the H2S·CO2 species. The structure of the complex has the CO2 and the S atom of H2S in a T-shaped configuration. The H2S plane is nearly orthogonal to the CO2–S plane with an angle of about 92° and the H2S·CO2 center-of-mass separation Rc.m. is 3.498(3) Å. [ABSTRACT FROM AUTHOR]

Microwave spectra for the SO2···H2S, SO2···HDS, and SO2···D2S complexes were measured using a pulsed beam, Fourier transform microwave spectrometer. Both a-dipole and c-dipole transitions were obtained. A total of 24 transitions were obtained for SO2···H2S, yielding A=8447.3(2), B=1762.004(7), C=1538.483(7) MHz, ΔJ=5.04(2) , ΔJK=65.46(9) , ΔK=-323(240) , δJ=0.63(1) and δK=38(3) kHz. For SO2···HDS, nine transitions yielded A=8229.7(6), B=1737.99(1), C=1519.69(2) MHz, ΔJ=4.4(4) and ΔJK=60(2) kHz, and for SO2···D2S, 11 transitions yielded A=8017.6(6), B=1715.24(2), C=1501.24(2) MHz, and ΔJ=3.8(4) , ΔJK=51(2) kHz. For the H2S data only, there are four possible structures for the complex which fit the data. When the deuterium isotope data are included, only two possible structures fit the data. There is only one structure which allows two O···H hydrogen bonds, and this is the structure we favor. This analysis basically gives a ‘‘stacked’’ structure with two O···H hydrogen bonds and a near Van der Waals radius contact between the two sulfur atoms. [ABSTRACT FROM AUTHOR]

The rotational spectrum of butadiene iron tricarbonyl was measured using a Flygare–Balle type microwave spectrometer. A total of 71 a-dipole and c-dipole transitions in the 5–17 GHz range were obtained for this asymmetric top transition metal complex. The ‘‘best fit’’ rotational constants are A=1005.4201(3) MHz, B=958.0408(2) MHz, and C=933.6865(3) MHz. Centrifugal distortion constants were also obtained in the least-squares fit to the measured transitions. The present measurements indicate an upper limit of 40 kHz for splittings due to internal rotation, which places a lower limit on the barrier height of V3 ≥ 1.2 THz. The measured rotational constants are used to determine CO bond angles and the distances between Fe and the butadiene C atoms. [ABSTRACT FROM AUTHOR]