62 nd International Symposium on Molecular Spectroscopy June 18-22, 2007 The Pure Rotational Spectra...

62nd International Symposium on Molecular Spectroscopy June 18-22, 2007

The Pure Rotational Spectra of

FeCN (X 6i) and FeNC (X 6i):

It Had to Be There!

M. A. Floryand

L. M. Ziurys

University of ArizonaDepartment of ChemistryDepartment of Astronomy

Steward Observatory


Importance of Metal Cyanides

NC Prussian Blue

Fe-NC and Fe-CN bondsVitamin B12Co-CN N

N

NN

N

NN

N

N

N

N

N

Fe2+

Fe3+

Fe2+

Fe

3+

Fe

3+

Fe2+

Fe3+

Fe2+

CRL618CRL618

• Metals bonded to CN Moiety - Found in many areas of chemistry (Biochemistry, Inorganic, Materials, etc.)

• Also important in Astrophysics - Most common metal carriers in interstellar gas - Tracers of nucleosynthesis - Window on dust condensation in evolved stars - MgCN, MgNC, AlNC, NaCN, KCN identified in several carbon-rich envelopes


NM C CNM

C N

M

Alkali-earth/main group M = Ca, Mg, Al, Ga, In

Transition metalsM = Cr, Co, Ni, Cu, Zn

Alkali metalsM = Na, K

• Also quite interesting spectroscopically• Three structures possible

LINEAR CYANIDE

T-SHAPED

LINEAR ISOCYANIDE

Sc Ti V Cr Mn Fe Co Ni Cu Zn

? ? ? CN ? ? CN CN CN CN

• Ziurys group pursuing 3d cyanides• Recorded pure rotational spectra of later 3d cyanides, recently CrCN• Iron analog remained elusive for over 10 years


Previous Work on FeNC/FeCN• Laser Fluorescence Spectroscopy (Lie and Dagdigian, 2001)

– Observed = 7/2′ ← ″ = 9/2 transition of FeN12C and FeN13C

– Determined B=9/2 = 4331(12) MHz

– Proposed 6 ground state; same as FeF and FeCl• Theoretical Calculations

– deYonker et al. (2004)

– Calculated Be(FeNC) = 4259 MHz; Be(FeCN) = 3708 MHz

– Predict that FeNC (X6 is more stable isomer by 0.6 kcal/mol– Hirano et al. (2006, 2007)

– Calculated Be(FeNC) = 4272 MHz; Be(FeCN) = 3714 MHz

– Predict that FeCN (X6 is more stable isomer by 0.4 kcal/mol

A bit confusing !!! Who is correct ??


A Sub-mm Search for FeCN/FeNC

• Fe(CO)5: 2 mTorr

– (CN)2: Trace (< 0.1 mTorr)

– Ar: 30 mTorr

– AC: 150 W (lower than usual)

• Much cleaner spectrum than with Oven

• Several unsuccessful attempts using Broida-type oven with Fe + (CN)2

puzzling, since this method worked for other 3d cyanides But.. It had to be there !• Attempted different synthetic method• VM machine with AC discharge

• Scanned continuously from 380-415 GHz (over 4 estimated rotational transitions)


FeCN/FeNC = 9/2J = 46.5 → 47.5

• Many harmonically-related features

• Spin-orbit and Renner–Teller

• Due to iron precursor and cyanogen

• Also reproduced with HCN

J = 50.5 → 51.5FeCN/FeNC = 9/2J = 46.5 → 47.5

Broida oven

BUT…rotational constant unexpected ~ 4085 MHzNOT 4331 MHz 4259 MHz 4272 MHz


Verify the Ground State Structure

• 4 isotopologues observed ( = 9/2)– 56FeCN (92 %)– 54FeCN (6 %)– 57FeCN (2 %)– 56Fe13CN (with H13CN as precursor)

Fe13CN = 9/2J = 49.5→50.5

CONCLUSION: This is FeCN !


FeNCJ=46.4→47.5 = 9/2Avg. of 3 scans

And FeNC (X 6i)…

• WEAKER set of transitions with higher B value

• 10 transitions measured in range 272-419 GHz

• Based on relative intensity

EFeNC-FeCN ≈ 1.7 kcal/mol

In MHz Sub-mm Lie & Dagdigian

B 4329.735(11) 4331(12)

D 0.0018788(69)

H 6.0(14)*10-9

rms 0.020

FeNC (X 69/2)

Complete Analysis awaits next graduate student…. (Robin ???)


Analysis In ProgressIn MHz FeCN (X 6i)

B 4085.07(69)

D 0.00142(12)

H -0.000000013(11)

A -1 887 724.275

AD -9.990(45)

AH 0.0000916(39)

13 000

D -0.31(12)

H 0.0000138(38)

-55 000(35 000)

D -0.65(37)

D 0.037(30)

-533(60)

-3.5(1.0)

0.035(30)

0.0056(24)

m~n

~

• Assigning other Spin-Orbit and Renner-Teller components

• 204 lines measured in 4 isotopologues

• 21 rotational transitions observed in range 140-500 GHz

• Analysis with effective case (a) Hamiltonian

Heff = HRot + HSO + HSS + HLD

o~

p~

BFeNC (Optical) = 4331 MHz

BFeNC (Theory) = 4259-4272 MHz

BFeCN (Theory) = 3708-3714 MHz

• Current rotational constant does not agree with any previous values


• Arizona’s FTMW system being used to study metal-bearing radicals• Discharge Nozzle with organometallic precursors• After ZnCN, move to FeCN and CrCN

As a check…An FTMW Study…

N = 2 – 1ZnCN~ 15 GHz


In Conclusion…at least thus far

• Grad student Mike Flory needs to finish analysis for PhD

• Pure rotational spectrum of FeCN has been measured in all spin components

• BUT…still need to complete assignment

• BFeCN is ~10% larger than calculations

• Bond lengths of FeCN determined• Spectrum of FeNC ( = 9/2) recorded:

work in progress• FeCN is the more stable structure• In pursuit of FTMW spectrum


And thanks to the Ziurys Group:(Soon to be, Dr.) Mike FloryDr. Aldo ApponiDr. Chandra SavageDr. DeWayne HalfenStefanie MilamEmily TenenbaumMing SunRobin Pulliam

The star of the show..

(…provided he finishes the analysis)

NSFNASA

62 nd International Symposium on Molecular Spectroscopy June 18-22, 2007 The Pure Rotational Spectra...

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