Assignment of mm- and smm-wave spectra of rare isotopologues of cyanamide and the rm

(1)

geometry of NH2CN

64th OSU International Symposium on Molecular Spectroscopy

Adam Krasnicki, Zbigniew KisielInstitute of Physics, Polish Academy of Sciences

Brenda P. Winnewisser, Manfred WinnewisserDepartment of Physics, The Ohio State University

The cyanamide molecule H2NCN

5 atoms, 9 normal modesμa = 4.3192(40) D, μc =-0.9559(33) DInversion transitions (0+-0-) due to tunnelingprotons through low potential barrier (469.12 cm-1) Previous studies by rotational spectroscopy

cmw: + ND2CN, NHDCN Millen et. al, J.Mol.Spectrosc. 8, 153 (1962)D & 15N-isototopologues Tyler et. al , J.Mol.Spectrosc. 43, 248 (1972)to 120 GHz: Johnson et. al Astrophys. J. 208, 245 (1976)srb analysis: + D & 15N Brown et. al, J.Mol.Spectrosc. 114, 257 (1985)to 500 GHz: + D Read et. al, J.Mol.Spectrosc. 115, 316 (1986)14N splitting: Brown et al., J.Mol.Spectrosc. 130, 213 (1988)FT far ir: Birk,Winnewisser, J.Mol.Spectrosc. 159, 69 (1993)ir to 980 cm-1: Moruzzi,Jabs,2Winnewisser, J.Mol.Spectrosc. 190, 353 (1998)mmw + ir 8-350 cm-1 + D Kisiel,Krasnicki,2Winnewisser, 63rd OSU, WK08, (2008)

astrophysical: Turner et al., Astrophys. J. 201, L149 (1975) Lines emission in Sgr B2

More background…

MMW spectra measured on BWO based spectrometers in Giessen and Köln118-179 GHz, 202-221 GHz, 570-650 GHzWolfgang Jabs, Giessen 1998

Transitions:

a – type: 0+→ 0+, 0-→ 0- μa=4.3192(40)Dc – type: 0+→ 0-, 0-→ 0+ μc=-0.9559(33)D

Reduced quartic-quadratic potentialV(z)=A(z4+Bz2)

z=const*mred*A-⅟2*Ф

The spectra

a – type (0+ → 0+, 0- → 0-)

c – type (0+ → 0-, 0- → 0+)

Experimental spectrum

The spectra of deuterated isotopologues of NH2CN

ND2CN NHDCN

NH2CN

aR, J” = 7, {0+, 0-}

Relative intensity:ND2CN : NHDCN : NH2CN 1 : 1 : 0.15

ND213C

N

aR, J” = 7, {0+, 0-}

The spectra of deuterated isotopologues of NH2CN

NHD13CN

NH213C

N

Relative intensity:ND2CN : NHDCN : NH2CN 1 : 1 : 0.1513C abundance 1.07%

15ND2CN

Relative intensity:ND2CN : NHDCN : NH2CN 1 : 1 : 0.1513C abundance 1.07%15N abundance 0.368%

aR, J” = 7, {0+, 0-}

The spectra of deuterated isotopologues of NH2CN

15NHDCN

NHDC15

NND2C15

N

The J = 8 ← 7 rotational transition in ND2C15N

Blue – 0+

White – 0-

15ND2CN, Ka=1, 0+ NHDCN, cQ, 0+→ 0-

The J = 8 ← 7 rotational transition in ND2C15N

Ka=5Ka=4

0+ 0- 0-0+ 2:1 alternation of statistical weights

Blue – 0+

White – 0-

The Hamiltonian

Hrot – Watsonian asymmetric rotor Hamiltonian (reduction A, represent. Ir)

H01 – interstate second order Coriolis coupling terms expressed in Reduced Axis System (H.M.Pickett, J.Chem.Phys., 1972, 56, 1715.)

H01 = (Fca + FcaJ P 2 + Fca

K Pz 2 + …) (Pc Pa + Pa Pc ) +

(Fbc + FbcJ P 2 + Fbc

K Pz 2 + …) (Pb Pc + Pc Pb )

H(0)rot + ΔE

H01

H01

H(1)rot

0+

0-

Simultaneous fit of

data for 0+ and 0- states with SPFIT of

H.M. Pickett

Fbc term used only for the HDNCN species

The fitted constants for ND2C15N

+ similar results for NH2

13CN, NHD13CN,ND2

13CN, NHDC15N,15ND2CN, 15NHDCN

E = 494551.901(27) MHz

Fca = 267.6102(19) MHz

For ND2CN

The 0+- 0- splitting as a test for correct assignment

ΔEisot.- ΔEND2CN ND213CN ND2C15N 15ND2CN

obs. / cm-1 0.022 -0.011 -0.633

calc./ cm-1 0.049 -0.064 -0.771

ΔE(0- - 0+) ND2CN

obs. / cm-1 16.4965304(9)

calc./ cm-1 15.387

ΔE(0- - 0+) NHDCN

obs. / cm-1 32.089281(4)

calc./ cm-1 31.062

ΔEisot.- ΔENHDCN NHD13CN NHDC15N 15NHDCN

obs. / cm-1 0.029 -0.001 -0.780

calc./ cm-1 0.062 -0.082 -0.986

ΔE(0- - 0+) NH2CN

obs. / cm-1 49.567984(4)

calc./ cm-1 49.567

ΔEisot.- ΔENH2CN NH213CN

obs. / cm-1 0.062

calc./ cm-1 0.069

Results from obtained by using the reduced quartic-quadratic potential

V(z)=A(z4+Bz2)and program ANHARM

A, B parameters scaled for isotopic species based on reduced mass for inversion

motion in cyanamide

Experimental r0, rm(1) and rm

(1L) geometries of cyanamide

r0 rm(1) rm

(1L)

r(N─H) /Å 1.0032(12) 1.0189(23) 1.0152(27)

r(N─C) 1.3445(57) 1.3448(17) 1.3434(17)

r(C≡N) 1.1632(59) 1.1650(18) 1.1641(17)

(HNH) /° 116.26(23) 112.32(24) 111.79(31)

(NCN) [180.0] [180.0] [180.0]

Φ 35.47(60) 41.67(90) 43.05(70)

ca /u1/2*Å -0.0550(93) -0.121(30)

cb-0.0194(11) -0.0146(24)

cc[0.0] [0.0]

δH0.028(12)

σfit / uÅ2 0.01545 0.00462 0.00431

Comparison of geometries of cyanamide

rm(1L)

this workMP2/aug-cc-pVTZ

this workaveraged rs str. Tyler et.al JMS ’72

semirigid benderBrown et.al JMS ’88

r(N─H) /Å 1.0152(27) 1.0096 1.001(15) [0.9994]

r(N─C) 1.3434(17) 1.3450 1.346(5) 1.3301(5)

r(C≡N) 1.1641(17) 1.1724 1.160(5) [1.1645]

(HNH) /° 111.79(31) 111.93 113(2) 120.78(46)

(NCN) [180.0] 176.65 [180] [175]

Φ 43.05(70) 44.74 38(1) 45.03(20)

• The mmw and smm rotational spectra of 7 rare isotopic species of cyanamide have been assigned , up to Ka=7 and J”=34 (ca 200 lines for each species).

• Spectroscopic information on 15ND2CN, ND2C15N has been considerably improved.

• The spectra of NH213CN, NHD13CN, ND2

13CN, 15NHDCN, NHDC15N have been assigned for the first time.

• The structure of cyanamide has been derived.

• We hope that further progress in understanding of the cyanamide geometry will come from semi-experimental equilibrium structure .

Conclusions

Acknowledgments

We are indebted to Wolfgang Jabs (Giessen) who recorded all of the spectra used in this work.

We are grateful to Ewa Bialkowska-Jaworska (Warszawa) for help with ab initio calculations.