FOURIER TRANSFORM MICROWAVE SPECTROSCOPY OF ALKALI METAL HYDROSULFIDES: DETECTION OF KSH P. M....

FOURIER TRANSFORM MICROWAVE SPECTROSCOPY OF ALKALI METAL HYDROSULFIDES: DETECTION OF KSH

P. M. SHERIDAN, M. K. L. BINNS, J. P. YOUNG Department of Chemistry and Biochemistry, Canisius College

M. P. BUCCHINO and L. M. ZIURYS Department of Chemistry, Astronomy and Steward Observatory, University of Arizona

Metal Hydrosulfides: Previous Work

• Laser Excitation Spectroscopy• CaSH and SrSH

• 2A′ - 2A′, 2A″ - 2A′, 2A′ - 2A′, transitions rotationally resolved (Bernath et. al; Steimle et al)

• bent geometry

• Millimeter-Wave Studies• MgSH 2A′) and CaSH 2A′) (Taleb-Bendiab and coworkers); • SrSH 2A′), BaSH 2A′), AlSH 1A′), CuSH 1A′) and isotologues

(Ziurys group)• bent geometry (M-S-H angle ~90°)

Alkali Metal Hydrosulfides: Previous Work

• Millimeter-Wave Spectra:− LiSH, 6LiSH, and LiSD (Janczyk and Ziurys)− NaSH and NaSD (Kagi and Kawaguchi)

• Bent Molecular Geometries

• r0 Structural Parameters Determined

• No Hyperfine Splitting (Alkali Metal or Deuterium) Resolved

• KSH and KSD (no previous experimental work)

FTMW and Alkali Metal Hydrosulfides

• Further Investigation of Alkali Metal Hydrosulfides• Measure metal hyperfine parameters to investigate metal-ligand

bonding character• Experimentally detect KSH and KSD, determine geometry,

structural parameters and hyperfine constants

• How? Using FTMW and Discharge Assisted Laser Ablation• Build on recent study of LiCCH, NaCCH, KCCH and deuterium

isotopologues

Fourier Transform Microwave Spectrometer

• 4 – 60 GHz

• Cyropumped vacuum chamber

• Fabry-Perot cavity

• Supersonic jet 40° relative to optical axis

• 400 kHz scan increments

Ziurys Laboratory FTMW

Fourier Transform Microwave Spectrometer

Ablation Laser

Molecular Jet

Cavity Mirror

Discharge Assisted Laser Ablation

• 35 psi backing pressure (open 750 ms)

• Ablation laser: Nd:YAG (532nm, 200 mJ per pulse; 10 Hz rep rate; 1200 ms delay)

• DC discharge 0-500 V (1400 ms)

• 500 - 3000 shots averaged

• Alkali metal vapor reacted with 0.25% H2S or D2S in Ar

Alkali Metal Rods

• Al support rod

• 3 cm long notch, diameter 2 mm smaller

• Li, Na and K pressed into notch under Ar

• Only alkali metal portion ablated

Initial Search: NaSH

• Millimeter-wave data of NaSH used to predict frequencies of low J transitions

• Metal hyperfine constants from alkali metal acetylides used to estimate hyperfine splittings

• I = 3/2 (Li, Na, K)

• F = J + I

NaSH (X1Aʹ) Spectrum~

J = 4 3 (Ka = 0)

F = 3 3F = 5 5

F = 5 4 6 5

F = 4 3 3 2

Lines and Assignments NaSH (X1Aʹ) (Ka = 0) J' J" F' F" nobs nobs - ncalc

1 0 1.5 1.5 11991.708 -0.002

2.5 1.5 11993.022 0.004

0.5 1.5 11994.066 0.002

4 3 4.5 4.5 47967.215 0.002

2.5 1.5 47968.381 0.011

3.5 2.5 47968.381 0.011

4.5 3.5 47968.531 0.010

5.5 4.5 47968.531 0.010

2.5 2.5 47969.678 <0.000

5 4 5.5 5.5 59957.418 0.004

3.5 2.5 59958.642 0.009

4.5 3.5 59958.642 0.009

5.5 4.5 59958.738 0.016

6.5 5.5 59958.738 0.016

3.5 3.5 59959.942 0.001

~

Initial Search: KSH

• Initial Rotational Constants− Scaled M-S bond length from alkali metal sulfides− Used S-H bond length and M-S-H angle from LiSH and NaSH

• Initially searched 10 MHz centered on J = 1 0 (Ka = 0) rotational transition

KSH (X1Aʹ) Spectrum

49833.5 49833.7 49833.9

J = 7 6 (Ka = 0)

F = 7 6 6 5

F = 9 8 8 7

Frequency (MHz)

~

Lines and Assignments KSH (X1Aʹ) (Ka = 0) J' J" F' F" nobs nobs - ncalc

1 0 1.5 1.5 7118.678 0.0152.5 1.5 7119.994 0.0070.5 1.5 7121.047 0.001

6 5 4.5 3.5 42715.569 0.0155.5 4.5 42715.569 0.0156.5 5.5 42715.633 0.0187.5 6.5 42715.633 0.018

7 6 5.5 4.5 49833.636 -0.0106.5 5.5 49833.636 -0.0107.5 6.5 49833.689 -0.0018.5 7.5 49833.689 -0.001

8 7 6.5 5.5 56951.150 -0.0357.5 6.5 56951.150 -0.0358.5 7.5 56951.190 -0.0289.5 8.5 56951.190 -0.028

~

MSH Rotational Constants

Parameter(MHz) NaSH [1] NaSH [2] KSH

A 292832.7 (4.9) 292947.8(7.5) 290148 (fixed)

B 6065.0184(36) 6065.0178(43)

C 5927.7737 (24) 5927.7725(62)

(B+C)/2 3646.3021(42)

caa (M) -5.23(39) -5.30(22)

rms 0.028 0.049 0.028

[1] Kagi and Kawaguchi, ApJ 491, L129 (1997)[2] Combined fit with previous millimeter-wave data; 3s uncertainties

• Nuclear spin-rotation could not be reliably determined for either metal

+

KSD Spectrum

KSD J = 8 7 and 7 6 (Ka= 0, DF = +1); deuterium hf not resolved

48607.8 48608.0 48608.2

J = 7 6 (Ka = 0) F1 = 6 5 5 4

F1 = 8 7 7 6

Frequency (MHz)

I1 = 3/2 (M)

I2 = 1 (D)

F1 = J + I1

F = F1+ I2

Constants MSD

[1] Kagi and Kawaguchi, ApJ 491, L129 (1997)[2] Combined fit with previous millimeter-wave data; 3s uncertainties

• Nuclear spin-rotation could not be reliably determined for either metal

• Deuterium hf not yet reliably determined

Parameter(MHz) NaSD [1] NaSD [2] KSD

A 150947.8 (5.4) 150943.0 (9.9) 150136.6 (fixed)

B 5976.2613 (54) 5976.2573 (120)

C 5730.7996 (15) 5730.8002 (108)

(B+C)/2 3545.24204 (45)

Caa (M) -5.24 (40) -5.7 (1.3)

rms

+ +

Quantum Calculations

LiSH [1] LiSH [2] NaSH [1] NaSH [2,3] KSH [1]M-S (Å) 2.167 2.146 2.519 2.479 2.845

S-H (Å) 1.343 1.353 1.343 1.354 1.344M-S-H (°) 93.8 93.0 93.8 93.1 95.7

[1] CCSD(T)/6-311++G(3df,2pd) Geometric Parameters[2] Janczyk and Ziurys, CPL 365, 514 (2002), r0 structure[3] Kagi and Kawaguchi, ApJ 491, L129 (1997), r0 structure

• Lowest energy geometry for KSH: bent

Species KSH [1] KSH KSD [1] KSD(B+C)/2 (MHz) 3463.761 3646.3021(42) 3378.652 3545.2420(45)

Hyperfine Parameters (MHz)

Species 7Li 23Na 39K

MF 0.41590 (12) -8.4401(15) -7.932397(10)M35Cl 0.24993(50) -5.6698(60) -5.66583(3)MOH 0.2958(15) -7.584(52) -7.454(52)MBH4 -3.385(31) -4.256(24)MCCH 0.378(47) -7.264(20) -6.856(18)MSH -5.23(26) -5.30(22)

• Nuclear quadrupole coupling small in magnitude and similar to other alkali-containing molecules consistent with M+ L- structure

Species M S HLiSH +0.50 -0.52 +0.02

NaSH +0.61 -0.62 +0.01KSH +0.88 -0.88 +0.01

HF/6-311++G(3df,2pd)//CCSD(T)/6-311++G(3df,2pd) Mulliken Atomic Charges

Future Work

• Ka = 1 components of MSH and MSD species

• LiSH • Further investigate ionic/

covalent bonding character

of other alkali metal

containing molecules

• Funding : Canisius College & NSF• David Ewing: Quantum Calculations