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FOURIER TRANSFORM MICROWAVE SPECTROSCOPY OF ALKALI METAL ACETYLIDES P. M. SHERIDAN, M. K. L. BINNS Department of Chemistry and Biochemistry, Canisius College.

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Presentation on theme: "FOURIER TRANSFORM MICROWAVE SPECTROSCOPY OF ALKALI METAL ACETYLIDES P. M. SHERIDAN, M. K. L. BINNS Department of Chemistry and Biochemistry, Canisius College."— Presentation transcript:

1 FOURIER TRANSFORM MICROWAVE SPECTROSCOPY OF ALKALI METAL ACETYLIDES P. M. SHERIDAN, M. K. L. BINNS Department of Chemistry and Biochemistry, Canisius College J. MIN, M. P. BUCCHINO, D. T. HALFEN and L. M. ZIURYS Department of Chemistry, Astronomy and Steward Observatory, University of Arizona

2 Metal Acetylides Experimental observation of CuCCH (X 1  + ) –Sun et al (Ziurys group) –MM-wave and FTMW measurements of several isotopologues –FTMW  discharge assisted laser ablation spectroscopy –Cu and D hyperfine parameters determined –Geometric and bonding properties Study other metal acetylides using the FTMW –AlCCH(MH ), ZnCCH (RC03), MgCCH (RC04) –Extensive millimeter-wave studies exist for the alkali metal acetylides –Further investigate metal-ligand bonding  hyperfine parameters

3 Alkali-Metal Acetylides: Previous Work LiCCH and 6 Li, 13 C & D isotopologues; ground and 5 vibrational states (Apponi, Brewster and Ziurys, 1998) NaCCH and D isotopologues; ground and 5 vibrational states (Brewster et al, 1999) KCCH and D isotopologues; ground vibrational state (Xin and Ziurys, 1998) Linear molecular geometries, structural parameters determined, no hyperfine splitting resolved Use FTMW to measure metal hyperfine parameters to investigate metal-ligand bonding character

4 Fourier Transform Microwave Spectrometer 4 – 40 GHz Cyropumped vacuum chamber Fabry-Perot cavity Supersonic jet 40° relative to mirror axis 400 kHz scan increments Ziurys Laboratory FTMW

5 Fourier Transform Microwave Spectrometer Ablation Laser Molecular Jet Cavity Mirror

6 Discharge Assisted Laser Ablation (DALAS) 40 psi backing pressure (open 500  s) Ablation laser: Nd:YAG (532nm, 200 mJ per pulse; 10 Hz rep rate; 990  s delay) DC discharge 1000 V (1000  s) shots averaged Alkali metal vapor reacted with 0.3% HCCH or DCCD in Ar S/N increased by ~ 10x with discharge

7 Alkali Metal Rods Al support rod 3 cm long notch, diameter 2 mm smaller Na and K pressed into notch under Ar Li superglued into notch under Ar Only alkali metal portion ablated Previous work ablated corresponding salt

8 Initial Search Millimeter-wave data of alkali metal acetylides used to predict frequencies of low J transitions Metal hyperfine constants from alkali chlorides used to estimate hyperfine splittings Searched 10 MHz section centered on a rotational transition

9 NaCCH (X 1 Σ + ) Spectrum ~

10 KCCH (X 1 Σ + ) Spectrum ~

11 LiCCH (X 1 Σ + ) Spectrum ~

12 Lines and Assignments MCCH LiCCHNaCCH KCCH J‘  J" F'  F" obs obs -  calc obs obs -  calc obs  obs -  calc NaCCH and KCCH  J = 3  2 and J = 4  3 Individual Hyperfine Lines Observed: LiCCH (3), NaCCH (19), KCCH (21)

13 Constants MCCH Parameter (MHz)LiCCH NaCCH KCCH B (32) (46) (86) (10) (77) (31) D (11) (14) (64) (48) (43) (13) H2.79(99)x (1.3)x (14)x (70) x (10)x (22)x10 -8 L3.257(76)x (13)x eQq (M)0.378(47)-7.264(20)-6.856(18) rms Combined fit with previous millimeter-wave data; 3  uncertainties Nuclear spin-rotation constant (C I ) could not be reliably determined for each metal

14 LiCCD (X 1 Σ + ) Spectrum ~ NaCCD and KCCD  J = 2  1, J = 3  2 and J = 4  3 Individual Hyperfine Lines Observed: LiCCD (7), NaCCD (16), KCCD (30)

15 Constants MCCD Parameter (MHz)LiCCD NaCCD KCCD B (21) (92) (91) (59) (58) (14) D (18) (69) (95) (88) (19) (21) H2.88(18)x (36)x (11)x10 -9 L1.77(20) x eQq (M)0.272(37)-7.442(47)-6.873(14) eQq (D)0.152(33)0.193(48)0.157(20) rms Combined fit with previous millimeter-wave data; 3  uncertainties Nuclear spin-rotation constant (C I ) could not be reliably determined for each metal or deuterium

16 Hyperfine Parameters (eQq) (MHz) Species 7 Li 23 Na 39 K MF (12) (15) (10) M 35 Cl (50) (60) (3) MOH0.2958(15)-7.584(52)-7.454(52) MBH (31)-4.256(24) MCCH0.378(47)-7.264(20)-6.856(18) MCCD0.272(37)-7.442(47)-6.873(14) Nuclear quadrupole coupling constants small in magnitude and similar to other alkali-containing molecules  consistent with M + L - structure Alkali-metal acetylides  bonding largely ionic SpeciesLiCCDNaCCDKCCDCuCCD eQq(D)0.152(33)0.193(48)0.157(20)0.214(23)

17 Future Work DALAS + Alkali Metal Pressed Rods May be a good synthetic method for other alkali metal molecules LiOD, NaOD, KOD MNH 2, MND 2 MSH, MSD MCH 3, MCD 3 Further investigate ionic/ covalent bonding character Funding : Canisius College & NSF


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