Is the Equilibrium Structure of BeOH Linear or Bent?

Kyle MascaritoloDr. Michael Heaven

Significance of ResearchMonohydroxides of Mg, Ca, Sr and Ba have all been studied experimentally and computationally

For the Ground State: Linear: CaOH, SrOH, BaOH [1-3]

– Ionic Bonding M+X-

Quasilinear: MgOH [4]

– Some Covalency, barrier to linearity < 2 cm-1

BeOH calculated to be bent, but little experimental data 1. D.O. Harris, J. Mol. Spectrosc. 97, 73 1983.

2. D.O. Harris, J. Mol. Spectrosc. 97, 37 1983.3. P.F. Bernath, J. Chem. Phys. 84, 698 1986.4. Y. Ni, Ph.D. thesis, Uni. California, Santa Barbara, 1986.

Past Computational Findings

Several high-level ab initio calculations for BeOH predict: [1-3]

– Equilibrium BeOH ranging ∠134° - 152°

– Barrier to linearity up to 136 cm-1,

but as low as 50 cm-1

– Near Prolate Top: B0 ≈ 1.29 cm-1

– A significant contribution of covalency to the Be-O bonding

1. Theodorakopoulos, Petsalakis, and Hamilton J. Chem. Phys. 111, 23 1999.2. Koput and Peterson J. Phys. Chem. A 107, 2003.3. Palke and Kirtman Chem. Phys. Lett. 117, 5 1985.

Barrier to Linearity: 136 cm-1

∠BeOH = 140.9°

Possibly quasilinear in ground state

Method: RCCSD(T) cc-pV5Z

Equilibrium Bending Potential with vl2 Bending Energy Levels

Koput and Peterson J. Phys. Chem. A 107, 2003.

-8000

-7000

-6000

-5000

-4000

-3000

-2000

-1000

100 110 120 130 140 150 160 170 180

Re

lativ

e E

ne

rgy

/cm

-1

Angle / degrees

X2A'

12A'

12A"

-3500

-3000

-2500

-2000

-1500

-1000

1.25 1.3 1.35 1.4 1.45 1.5 1.55 1.6

Re

lativ

e e

ne

rgy

/cm

-1

R(BeO) /A

12A"

CASSCF/MRCI/ aug-cc-pVTZ

12A” State Calculations

R(BeO)=1.457, R(OH)=0.954, q=127.6; B0=1.228 cm-1

Calculations done by Dr. Michael Heaven

Excited states shifted down for comparison

Renner-Teller

Past Experimental Results

Low resolution gas phase electronic spectroscopy

– 300 – 330nm(30300 – 33330 cm-1)– Was not analyzed in detail

A. Antic-Jovanovic, V. Bojovic, D. Pesic, Spectrosc. Lett. 21, 8 1988.

Experimental Setup: Laser Induced Fluorescence and 1 + 1’ Resonance Enhanced Multiphoton Ionization Spectroscopies

LIF and REMPI Excitation Photon: Doubled output of 2nd Harmonic Nd:YAG pumped dye laser (Quanta Ray PDL1)REMPI Ionization Photon: 248nm from KrF Excimer (COMPexPro 102)Ablation Photon: Fundamental of Nd:YAG (Continuum Mini-Lite II)

Base Pressure: 1x10-7 Torr

Base Pressure: 1x10-9 Torr

Smalley Laser Ablation

1 + 1’ REMPI Survey

30400 30800 31200 31600 32000 32400 32800

400

500

600

Wavenumbers (cm-1)

BeOH

BeOD

752 cm-1708 cm-1

579 cm-1561 cm-1517 cm-1

0000

Transitions from 0000

0200

?

0110

00000110 03100200

Negative Anharmonicity of MgOH/OD

Y. Ni, Ph.D. thesis, Uni. California, Santa Barbara, 1986.

Laser Induced Fluorescence

31000 31250 31500 31750 32000 32250 32500

0

200

400

600

800

BeOD

BeOH

Wavenumber (cm-1)

30850 30900 30950 31000 31050

0

100

200

300

400

500

600

700

BeOD

BeOH

Wavenumber (cm-1)

LIF of Current Lowest Rovibronic Transition

K’=0 ← K”=1

K’=2 ← K”=1

K’=1 ← K”=0

K’=1 ← K”=0

K’=0 ← K”=1BeOH

Perpendicular transitions

Energy Level Diagram for Prolate Top∆K = ±1 ∆J = 0,±1E = BJ(J+1)+(A-B)K2

J=01

2

3

J=0

1

2

3

1

2

3

1

2

3

2

3

2

3

K=0 K=1 K=2

v”

v'

≈160 cm-1 BeOH≈100 cm-1 BeOD

T = 15KkT ≈ 11 cm-1

≈40 cm-1 BeOH≈26 cm-1 BeOD

BeOD

30860 30880 30900 30920 30940 30960 30980 31000 31020 31040 31060Wavenumber/cm-1

0.1

0.2Nor

mal

ized

Inte

nsity

/ cm

-1

Obs.

Calc.

BeOH

” = 1.2150(58) cm-1

’ = 1.2044(49) cm-1

T = 15K

K’=0 ← K”=1 K’=1 ← K”=0 K’=2 ← K”=1

BeOD

30860 30880 30900 30920 30940 30960 30980 31000 31020 31040 31060Wavenumber/cm-1

0.1

0.2Nor

mal

ized

Inte

nsity

/ cm

-1

Obs.

Calc.

BeOH

” = 1.2150(58) cm-1

’ = 1.2044(49) cm-1

T = 15K

K’=0 ← K”=1 K’=1 ← K”=0 K’=2 ← K”=1

K’ = 2 ← K”=1?

31025 31030 31035 31040 31045 31050 31055 31060 31065Wavenumber/cm-1

0.005

0.010

Norm

alize

d In

tens

ity /

cm-1

Q

R(0) R(1) R(2)P(1)P(2)P(3)P(4)

R(1)R(2)

P(3)P(4)

Q

Be2O?

BeOD

30860 30880 30900 30920 30940 30960 30980 31000 31020 31040 31060Wavenumber/cm-1

0.1

0.2Nor

mal

ized

Inte

nsity

/ cm

-1

Obs.

Calc.

BeOH

A”-A' ≈ 20 cm-1

” = 1.2150(58) cm-1

’ = 1.2044(49) cm-1

T = 15K

K’=0 ← K”=1 K’=1 ← K”=0 K’=2 ← K”=1

30850 30900 30950 31000 31050

0

100

200

300

400

500

600

700

BeOD

BeOH

Wavenumber (cm-1)

LIF of Current Lowest Rovibronic Transition

K’=0 ← K”=1

K’=2 ← K”=1

K’=1 ← K”=0

K’=1 ← K”=0

K’=0 ← K”=1BeOH

30965 30970 30975 30980 30985 30990 30995 31000 31005 31010 31015Wavenumber/cm-1

0.1

0.2

Norm

aliz

ed Inte

nsity / c

m-1

30850 30855 30860 30865 30870 30875 30880 30885 30890Wavenumber/cm-1

50

100

/1e-

6N

orm

aliz

ed In

tens

ity /

cm-1

BeOH

A”-A’ ≈ 40 cm-1

” = 1.247(14) cm-1

= 1.241(12) cm-1

T = 15K

BeOD

K’=1 ← K”=0

K’=0 ← K”=1

Simulation done with PGOPHER

1 + 1’ REMPI Survey

30400 30800 31200 31600 32000 32400 32800

400

500

600

Wavenumbers (cm-1)

BeOH

BeOD

If we have K’=0 ← K”=1,then why no K’=2 ← K”=1?

BeOH

BeOD

Constants”

0000 1.246(14) 1.2453(86)

0110 1.2485(84) 1.2461(88)

0000 1.280(15) 1.224(13)

”

0000 1.1892(86) 1.1860(63)

0110 1.134(11) 1.1333(96)

0200 1.0934(80) 1.0922(87)

0310 1.106(27) 1.100(21)

So is it bent?We think so.

Future Work

• Explore to higher and lower energy• Make spectra “hot” by increasing ablation

laser power to populate K” = 1,2,…• PFI-ZEKE to get geometry of cation• Find ionization potential

Acknowledgements

LabmatesIvan AntonovKeith FreelJoshua BartlettMichelle SullivanJiande Han

Past WorkJeremy Merritt

Thank you.

Quasilinear MgOH/OD

rx/re = 1.38 for MgOH stated by Murad

rx > 2re to be ionic (rx = 2.5 Å, re = 1.8 Å)

rx

E. Murad, J. Chem. Phys. 75 1983.

Ground State Bending Potential of BeOH at Different RBe-O Bond Lengths

RBe-O ≤ 2.4 Bohr → Linear

RBe-O ≥ 2.4 Bohr → Bent

Calculated Equilibrium:RBe-O = 2.6 Bohr (1.3775 Å) at BeOH = 142.5°∠

Barrier to Linearity = 50 cm-1

Method: MRD-CITheodorakopoulos, Petsalakis, and Hamilton J. Chem. Phys. 111, 23 1999.

Past Experimental Results

• Ar Matrix-isolated ESR spectroscopy [1]

– Assumed ionic– Small evidence of bent

structure taken as false signal

• Low resolution gas phase electronic spectroscopy [2]

– 300 – 330nm(30300 – 33330 cm-1)– Was not analyzed in detail 1. J.M. Brom, Jr. and W. Weltner, Jr. J. Chem. Phys. 64, 9 1976.

2. A. Antic-Jovanovic, V. Bojovic, D. Pesic, Spectrosc. Lett. 21, 8 1988.

29360 29365 29370 29375 29380 29385 29390 29395 29400

Be18OH

Be16OH

Be

OH

+ io

n C

urr

en

t

Enegry /cm-1

31 74 0 31 74 5 31 75 0 31 75 5 31 76 0 31 76 5 31 77 0Wa v e nu mb er/c m-1

0 .0 5

0 .1 0

No

rma

lize

d In

ten

sity

/ cm

-1

LIF of 2A”- X2A’: Be16OH & Be18OH

Simulation with B’=1.22, B”=1.28 cm-1 T=20 K

obs.

calc.

Effects of Isotopic Substitution

Work done by Jeremy Merritt: M. Heaven

Doesn’t show asymmetric splittings. Deuteration needed to characterize bending motion.

30860 30870 30880 30890 30900 30910 30920 30930 30940 30950Wavenumber/cm-1

0.1

0.2

Norm

alize

d In

tens

ity /

cm-1

BeOD

Without High Energy SatelliteA” = 26.85(50) cm-1

” = 1.1892(86) cm-1

A’ = 46.399(53) cm-1

’ = 1.1860(63) cm-1

T = 15K

With High Energy SatelliteA” = 26.885(48) cm-1

” = 1.2150(58) cm-1

A’ = 46.465(16) cm-1

’ = 1.2044(49) cm-1

T = 15K

Laser Induced Fluorescence

31000 31250 31500 31750 32000 32250 32500

0

200

400

600

800

BeOD

BeOH

Wavenumber (cm-1)

BeOD

31975 32000 32025 32050 32075 32100

100

200

300

400

BeOD

BeOH

Wavenumber (cm-1)

00000110

v2 predicted at 52.9 cm-1

Koput and Peterson J. Phys. Chem. A 107, 2003.

30965 30970 30975 30980 30985 30990 30995 31000 31005 31010 31015Wavenumber/cm-1

0.1

0.2

Norm

aliz

ed Inte

nsity / c

m-1

30850 30855 30860 30865 30870 30875 30880 30885 30890Wavenumber/cm-1

50

100

/1e-

6N

orm

aliz

ed In

tens

ity /

cm-1

BeOH

A” = 79.455(84) cm-1

” = 1.247(14) cm-1

A’ = 46.241(89) cm-1

’ = 1.241(12) cm-1

T = 15K

BeOD

K’=1 ← K”=0

K’=0 ← K”=1

Simulation done with PGOPHER

∠BeOH” = 167.8°∠BeOH’ = 158.6°

BeOD

30860 30880 30900 30920 30940 30960 30980 31000 31020 31040 31060Wavenumber/cm-1

0.1

0.2Nor

mal

ized

Inte

nsity

/ cm

-1

Obs.

Calc.

BeOH

A” = 26.885(48) cm-1

” = 1.2150(58) cm-1

A’ = 46.465(16) cm-1

’ = 1.2044(49) cm-1

T = 15K

K’=0 ← K”=1 K’=1 ← K”=0 K’=2 ← K”=1

∠BeOH” = 141.2°∠BeOH” = 158.7°

BeOH

BeOD

ConstantsA” ” A’

0000 85.630(50) 1.246(14) 40.168(85) 1.2453(86)

0110 82.3764(28) 1.2485(84) 47.610(68) 1.2461(88)

0000 73.289(23) 1.280(15) 59.069(89) 1.224(13)

A” ” A’

0000 26.85(50) 1.1892(86) 46.399(53) 1.1860(63)

0110 26.978(71) 1.134(11) 47.353(70) 1.1333(96)

0200 26.8146(45) 1.0934(80) 49.736(48) 1.0922(87)

0310 21.21(14) 1.106(27) 58.90(13) 1.100(21)