62 nd international symposium on molecular spectroscopy june 18-22, 2007 the pure rotational spectra...
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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
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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 ??
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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)
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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 !
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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 ???)
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
• 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
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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
62nd International Symposium on Molecular Spectroscopy June 18-22, 2007
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