r. s. ram et al- infrared emission spectroscopy of the [10.5]^5-delta-x^5-delta system of vf

8/2/2019 R. S. Ram et al- Infrared emission spectroscopy of the [10.5]^5-Delta-X^5-Delta system of VF

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Infrared emission spectroscopy of the 10.55X5 system of VF

R. S. RamDepartment of Chemistry, University of Arizona, Tucson, Arizona 85721

P. F. BernathDepartment of Chemistry, University of Arizona, Tucson, Arizona 85721, and Department of Chemistry,University of Waterloo, Waterloo, Ontario N2L 3G1, Canada

S. P. Davis

Department of Physics, University of California, Berkeley, California 94720

Received 5 December 2001; accepted 5 February 2002

The emission spectrum of VF has been investigated in the 340017 000 cm1 region using a Fouriertransform spectrometer. The bands were excited in a high temperature carbon tube furnace from thereaction of vanadium metal vapor with CF4 , as well as in a microwave discharge through a flowingmixture of VF4 vapor and helium. Several bands observed in the 900012 000 cm

1 region havebeen attributed to VF. The bands with high wave number R heads near 9156.8, 9816.4, 10 481.4,11 035.8, and 11 587.2 cm1 have been assigned as the 0-2, 0-1, 0-0, 1-0, and 2-0 bands,respectively, of the new 10.55X5 system of VF. A rotational analysis of the 51

51 ,52

52 ,53

53 , and54

54 subbands of the 0-1, 0-0, 1-0, and 2-0 bands has been carriedout and spectroscopic parameters for VF have been obtained for the first time. The followingequilibrium constants have been determined for the ground state of VF by averaging the constants

of the different spin components: G(1/2)665.10 cm1, B e0.3863 cm1, e0.0028 cm1, and re1.7758 . 2002 American Institute of Physics.DOI: 10.1063/1.1464831

INTRODUCTION

Spectroscopic studies of transition metal-containingmolecules provide insight into chemical bonding in simplemetal systems.1 Because of the high cosmic abundance oftransition metal elements in stars, transition metal-containingmolecules are of astrophysical importance.2,3 While many ofthe diatomic transition metal oxides4 and hydrides5 have

been relatively well characterized, and many of the nitrideshave recently been investigated,6,7 only a few transitionmetal halides have been studied so far. In the group V tran-sition metal family only limited spectroscopic data are avail-able for TaCl,8 VCl,9 and VF10 from previous low resolutionstudies. The TaCl bands were observed from the microwaveexcitation of a mixture of TaCl4 vapor, N2 , and He during asearch for TaN bands, and were left unassigned.8 The visiblebands of VCl are also known9 but their rotational analysis isstill lacking. However, in a recent study of VCl we haveobserved a complex 5 5 transition in the near infraredwhich has been labeled as the 7.05X5 transition11 andwe have determined the spectroscopic constants from the ro-

tational analysis of a few bands. A number of low resolutionemission bands of VF have also been observed in the visibleregion by Jones and Krishnamurty10 and the electronic as-signments of 5 5 or 5 5 have been proposed. Norotational analysis of any VF bands has been reported todate.

Several theoretical studies of the spectroscopic proper-ties of VF12,13 and the related molecule VH14 have been car-ried out in recent years. Averyanov and Khait12 have per-formed an ab initio calculation of the spectroscopicproperties of the low-lying quintet states of VF and proposed

a 5 ground state. In another ab initio study, the spectro-scopic properties for the low-lying electronic states of VFhave been predicted by Harrison.13 In this study, the groundstate of VF was predicted to be either a 5 or a 5 state butno definite conclusion was drawn.13 However, a 5 groundstate has been predicted for VH by Bruna et al.14 on the basisof a high quality ab initio calculation. Transition metal ha-lides are expected to have a similar electronic structure as the

corresponding hydrides, so that 5 ground states are ex-pected for VF and VCl based on the available results forVH.14

In the present work we report on the observation of anew 0 transition of VF in the 900012 000 cm1 re-gion. The 0-0 band is located near 10 481 cm1, so this tran-sition has been labeled as 10.55X5 on the basis of arotational analysis of the 51

51 ,52

52 ,53

53 ,and 54

54 subbands of the 0-1, 0-0, 1-0, and 2-0 bands.The 50

50 subband could not be identified in ourspectra because of extensive overlapping from the other sub-bands.

EXPERIMENT

The near infrared spectra of VF were recorded in twoexperiments. In the first experiment the bands were observedin the reaction of vanadium atoms with CF4 in the presenceof100 Torr of He in a high temperature carbon tube fur-nace operated at a temperature of about 2200 C. The emis-sion from the furnace was focused on to the entrance aper-ture of the 1-m Fourier transform spectrometer of theNational Solar Observatory at Kitt Peak, equipped with a UVbeam splitter. The 30009400 cm1 region was recorded us-

JOURNAL OF CHEMICAL PHYSICS VOLUME 116, NUMBER 16 22 APRIL 2002

70350021-9606/2002/116(16)/7035/5/$19.00 2002 American Institute of Physics

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ing InSb detectors and a RG 645 filter, at a resolution of 0.05cm1. Six scans were coadded in about 18 min of integra-tion. The 900017 000 cm1 region was recorded usingmidrange photodiode detectors by coadding two scans inabout 6 min of integration. In spite of the short integrationtime, the spectrum was observed with sufficient signal-to-noise ratio to be suitable for rotational analysis.

In the second experiment the bands were excited in a

microwave discharge lamp with a flowing mixture of VF4vapor and He. The spectra in the 850012 500 cm1 regionwere recorded at a resolution of 0.02 cm1 by coadding 25scans in 2.5 h of integration. This time the spectrometer wasequipped with a CaF2 beam splitter and the spectra wererecorded using Si photodiode detectors and a RG850 filter. Inthis experiment the 1-0 band of VF was observed with suf-ficient intensity for a rotational analysis and the lines wererelatively well resolved. This cooler spectrum was very help-ful in the rotational analysis of the other bands recorded us-ing the high temperature carbon tube furnace.

The new near infrared emission bands were readily at-tributed to VF based on their vibrational intervals and rota-

tional line spacing. The spectral line positions were mea-sured using a data reduction program called PC-DECOMPdeveloped by J. Brault. The peak positions were determinedby fitting a Voigt line shape function to each experimentalfeature. The furnace spectrum also contained the vibration-rotation bands of HCl and HF as impurities in addition to theVF bands and V atomic lines. We have used the HF 15 linepositions to calibrate our spectra. The molecular lines appearwith approximate widths of 0.075 cm1 furnace and 0.040cm1 microwave discharge and a maximum signal-to-noiseratio of about 13:1. The line positions are expected to beaccurate to 0.007 cm1. However, there is considerableoverlapping and blending due to the rotational structure ofdifferent subbands in the same region, so the uncertainty issomewhat higher for blended and weaker lines.

RESULTS AND DISCUSSION

A number of new VF bands were observed in the 900015 000 cm1 interval in the furnace spectrum, of which thebands observed in the 900012 000 cm1 region were themost intense. Prominent bands with R heads near 9156.8,9816.4, 10 481.4, 11 035.8, and 11 587.2 cm1 can readilybe identified as the 0-2, 0-1, 0-0, 1-0, and 2-0 bands of a newelectronic transition on the basis of their intensity and vibra-

tional spacing. The bands present in the 12 00015 000cm1 region are very weak and their heads could not bemeasured precisely. Much improved spectra of this regionare necessary before any interpretation of the visible bandscan be offered. A compressed portion of the near infraredtransition of VF is presented in Fig. 1. As seen in Fig. 1, eachband appears to be very complex because of the overlappingof the rotational structure of different subbands of a highmultiplicity transition.

In our previous studies of transition metal halides wehave noted a similarity between the electronic energy levelsof transition metal halides and the corresponding hydrides.For example, the structure of TiF16 and TiCl17 closely re-

sembles that of TiH,18 the electronic structure of HfCl19 issimilar to that of HfH20 and the electronic structure ofScF21,22 is very similar to that of ScH.23,24 This suggests thatthe electronic structure of VF is likely to be similar to that ofVH and VCl. In a recent theoretical predictions for VH,Bruna14 has predicted a 5 ground state and a strong5X5 transition near 10 650 cm1. Indeed, we have ob-served a strong but perturbed transition (5 5?) of VH25

near 7400 cm1

. For VCl, we have recently observed a nearinfrared electronic transition near 7004 cm1 which has beenassigned as the 7.05X5 transition. The new transitionof VF observed near 10 481 cm1 is analogous to the nearinfrared transitions of VCl11 and VH.25

The two 5 states of VF are expected to display Hundscase a coupling leading to five subbands, 50

50 ,51

51 ,52

52 ,53

53 , and54

54 . Because ofsevere overlapping from different subbands, the rotationalstructure of only the 51

51 ,52

52 ,53

53 , and54

54 subbands could be identified in our spectra. A por-tion of the 0-0 band near the R heads is provided in Fig. 2, inwhich the heads of the four assigned subbands have been

marked. The 50 50 subband still remains to be iden-tified. Our analysis indicates the presence of-doubling inthe 51

51 and52

52 subbands. The subband with thelargest -doubling has been assigned as the 51

51 sub-band. The observed pattern of rotational constants and rela-tive magnitude of the -doubling in the 51

51 and52

52 subbands has been very helpful in the-assignment. Normally -doubling is expected to be verysmall for states and should have a J-dependence26 given byJ(J1) . However, mixing of the ground X 5 state withthe nearby 5 state i.e., some Hunds case c behaviorwould lead to observable -doubling in the transition. In the

FIG. 1. A compressed portion of the 10.55X5 transition of VF.

FIG. 2. A portion of the 0-0 band of the 10.55X5 transition of VFwith the R heads marked.

7036 J. Chem. Phys., Vol. 116, No. 16, 22 April 2002 Ram, Bernath, and Davis



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51 51 subband the -doubling should increase as J(J

1) similar to that found in a normal 1 1 transitionwhile in the 52

52 subband the -doubling, if present,should increase as J(J1) 2. The presence of large-doubling in the 51 and

52 spin components is the resultof strong interactions with the nearby 5 state.

We have analyzed the rotational structure of only the51

51 ,52

52 ,53

53 , and54

54 subbands inthe 0-1, 0-0, 1-0, and 2-0 bands. The rotational analysis ofthe 0-2 band could not be achieved because of its weak in-tensity Fig. 1. The rotational structure of each subband con-sists ofR and P branches no Q branch appearing with simi-lar intensity consistent with a 0 assignment. Therotational constants for the different states have been ob-tained by fitting the observed lines to the following energylevel expression:

FvJT

vB

vJJ1D

vJJ1 2H

vJJ13

LvJJ1 41/2q

vJJ1qDvJJ1

2

qHJJ13qLJJ1

4. 1

The rotational lines were given weights according to theresolution, line intensity, and the extent of blending. Thebadly blended lines were heavily deweighted. The observedlines positions for the different sub-bands are available fromEPAPS27 or from the authors upon request. The molecularconstants for the different bands are provided in Table I. Thee/f parity assignment in the 51

51 and52

52 sub-

bands was made arbitrarily to provide a positive -doublingconstant qv

in lower state. The constants Tv

, Bv

, Dv

, Hv

,and L

vare required for most of the vibrational levels of the

different spin components. In addition the -doubling con-stants q

v, qDv , qHv , and qLv are required for the

51 and52 spin components to minimize the standard deviation ofthe fits. The determination of the higher order constants is areflection of the strong interaction with nearby states.

Although the visible spectrum of VF has been known fordecades, the identity of the ground state has been an openquestion. The present work provides the first high resolutiondata for VF and sheds some light on the nature of the groundelectronic state. The observation of several subbands for

TABLE I. Rotational constants in cm1 for the X5 and 10.55 states of VF. Note: Numbers in parenthesis are one standard deviation in the last digits.

Constants

X 51 X52

v0 v1 v0 v1

Tvv

0.0 664.830654 0.0 664.909638B

v0.381 78520 0.378 96428 0.384 89718 0.381 91219

106Dv

2.43919 2.31628 0.903972 0.885376109H

v0.83912 0.73515 0.0187281 0.0169587

1013Lv

1.41028 1.14331

102qv 1.313043 1.325946 0.107423 0.101223106qDv 8.02838 7.79349 0.717884 0.74510109qHv 2.38623 2.17129 0.165224 0.1716331013qLv 3.25955 2.71762 0.112924 0.120736

Constants

X 53 X54

v0 v1 v0 v1

Tvv

0.0 665.101978 0.0 665.558842B

v0.385 36133 0.383 18236 0.387 40917 0.384 19017

106Dv

5.82641 6.01544 0.807641 0.778140109H

v1.49523 1.51624

1013Lv

1.82245 1.80144

Constants

10.551 10.552

v0 v1 v2 v0 v1 v2

Tvv

10 473.191234 11 027.189426 11 579.995950 10 464.793726 11 019.174724 11 570.712134B

v0.340 32122 0.338 11116 0.334 84125 0.347 04819 0.344 30420 0.341 29522

106Dv

0.28115 0.469556 0.40321 0.837272 0.83910 0.794121010H

v0.28837 1.06962 0.146482 0.06919 0.56823

103qv

1.94043 1.38839 2.67142 0.96521 0.97623 1.14424106qDv 1.21431 0.79420 1.39130 0.065432 0.119468 0.211131010qHv 2.29692 0.94733 1.97087 0.458331014qLv 1.78499

Constants

10.553 10.554

v0 v1 v2 v0 v1 v2

Tvv

10 478.704355 11 033.263853 11 584.890044 10 447.986246 11 002.811641 11 551.363134B

v0.335 51419 0.332 90022 0.330 33244 0.355 00722 0.351 84924 0.349 99120

106Dv

0.367159 0.380484 0.26463 1.81117 1.72820 1.923101010H

v 4.0038 1.42069 1.37384 1.47122

1013Lv

1.12578 0.086396 0.09712

7037J. Chem. Phys., Vol. 116, No. 16, 22 April 2002 Emission spectroscopy of VF



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each vibrational band is consistent with the assignment of thehigh multiplicity transition. Our assignment of the 5 groundstate is consistent with available results for VH14 and ourrecent observation of an infrared electronic transition ofVCl.11 In a more recent study of VCl, an ab initio calculationhas been performed on the low-lying electronic states, andthe analysis of the 7.05X5 transition has been ex-tended by analyzing many more bands.28 It was also possible

to identify an additional subband in spite of severeblending.28 This study supports our 5 assignment for theground state of VCl11 and suggests that VF should also havea 5 ground state. Note, however, that the previouslysuggested10 5 ground state assignment for VF cannot becompletely ruled out.

An irregular variation in the rotational and distortionconstants of the different spin components of both theground and excited states is the result of strong interactionwith close-lying states. The large -doubling in the 51 and52 spin components is most probably the result of stronginteractions with close-lying 5 states. The effects of theseinteractions are also apparent in the observed local and glo-

bal perturbations. In the 0-0 and 1-0 bands of the 51 51subband, the lines with e-parity are affected for J45. Thehigh J e-parity lines could not be identified with certaintywhile the f-parity levels are unaffected. The 52

52 sub-band is free from local perturbations. In the 53

53 sub-band the observed minus calculated difference in the linepositions of the 0-1 and 0-0 bands suggests that v0 and 1levels are affected for J50. Similarly, the negative valueof the distortion constant of the v2 vibrational level ofthe 53 spin component of the excited state is the result ofinteractions in the excited state. The 54

54 subband isalso free from local perturbations, although in the 0-0 band

of the

5

4

5

4 subband the lines seem to split into twocomponents after approximately J52. The split lines in the4 subband were not included in the fit because of theirpoor intensity.

We have used the observed band head positions to cal-culate approximate vibrational constants for VF. The locationof the highest wave number R head of the 0-2, 0-1, 0-0, 1-0,and 2-0 bands near 9156.8, 9816.4, 10 481.4, 11 035.8, and11 587.2 cm1, respectively, provides the following approxi-mate vibrational constants for the ground and excitedstates of VF: e670.4 cm

1, ex e2.7 cm1, e

557.4 cm1, and ex e1.5 cm1. The ground state vi-

brational constants from this transition are, however, consid-

erably different from those reported by Jones andKrishnamurthy10 from the low resolution emission spectrumof the visible bands.

The spectroscopic constants for the different vibrationallevels of the ground and excited states provided in Table Ihave been used to determine approximate Hunds case aconstants. Because the constants of the different spincomponents of the ground and excited states vary in anirregular manner, a simple average of these constants hasbeen taken to obtain approximate Hunds case a constants.The average of the ground state vibrational intervalsfrom Table I provides G(1/2)665.10 cm1. The aver-age of the B values listed in Table I provides B0

0.3849 cm1, and B10.3821 cm1 yielding B e

0.3863 cm1, e0.0028 cm1, and re1.7758 . A

calculation for the excited state results in the valuesof G(1/2)554.44 cm1, G(3/2)551.13 cm1, B00.3445 cm1, B10.3418 cm

1, and B20.3393 cm1.

The excited state equilibrium constants using these valuesare e557.75 cm

1, exe1.66 cm1, B e0.3458

cm1, e0.0026 cm1, and re1.8769 .

The lowest energy term of the V

atom is a 5D , whicharises from the 3 d4 configuration.29 The a 5D term is splitby the ligand field of F and correlates to the 5, 5, and5 molecular states in order of increasing energy. The firstexcited term in V is a 5F at 3000 cm1 arising from the3d34s 1 configuration.29 The molecular states correlating tothe a 5F term are 5, 5, 5, and 5 states which form acluster of states in the 700010 000 cm1 range as calcu-lated for VH.14 Our near infrared transition of VF is, there-fore, between the two 5 states derived from the a 5D anda 5F terms of V. A 5 ground state for VF has been pre-dicted by Averyanov and Khait12 as does a high level calcu-lation by Bruna et al. on VH,14 although the ab initio calcu-

lation of Harrison13 on VF did not lead to a definiteconclusion about the identity of the ground state either 5or 5.

Some useful conclusions can be drawn from the spectro-scopic constants listed in Table I. The significant -doublingin the 51 and

52 spin components of both states indicatesthat they are strongly mixed with the spin components ofnearby states. Averyanov and Khait12 predict a 5 state at1700 cm1 above the X 5 state for VF, while for VH a 5state is predicted at about 800 cm1 above the ground state.This is also consistent with the Harrisons theoreticalpredictions13 for VF which suggests very close-lying 5 and5 states. The large -doubling in the ground state is there-fore due to strong interaction with this 5 state. Similarinteractions are also possible for the excited 5 state, al-though an ab initio calculation predicting all the low-lyingstates of VF is still lacking.

CONCLUSION

We have observed the thermal emission spectrum of VFin the 340017 000 cm1 region using a Fourier transformspectrometer. Five groups of bands with R heads highestwave number subband near 9156.8, 9816.4, 10 481.4,11 035.8, and 11 587.2 cm1 have been assigned as the 0-2,

0-1, 0-0, 1-0, and 2-0 bands of the 10.55X5 transition.The 1-0 band of this transition has also been observed usinga microwave discharge lamp. A rotational analysis of the51

51 ,52

52 ,53

53 , and54

54 , subbands ofthe 0-1, 0-0, 1-0, and 2-0 bands has been obtained and mo-lecular constants have been extracted. The large -doublingobserved in the 51 and

52 spin components is probably areflection of a strong interaction with nearby 5 states. Thelower 5 state is most likely the ground state of VF aspredicted,12,13 and observed for VCl11,28 but we do not haveany direct evidence to prove this. Further experimental andtheoretical work on VF will be necessary to confirm ourassignments.

7038 J. Chem. Phys., Vol. 116, No. 16, 22 April 2002 Ram, Bernath, and Davis



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ACKNOWLEDGMENTS

The authors thank J. Wagner, C. Plymate, M. Dulick, andD. Branston of the National Solar Observatory for assistancein obtaining the spectra. The National Solar Observatory isoperated by the Association of Universities for Research inAstronomy, Inc., under contract with the National ScienceFoundation. The research described here was supported byfunding from NASA laboratory astrophysics program. Some

support was also provided by the Natural Sciences and En-gineering Research Council of Canada.

1 C. W. Bauschlicher, Jr., S. P. Walch, and S. R. Langhoff, Quantum Chem-istry: The Challenge of Transition Metals and Coordination Chemistry,edited by A. Veillard, NATO ASI Ser. C Reidel, Dordrecht, 1986.

2 C. Jascheck and M. Jascheck, The Behavior of Chemical Elements in StarsCambridge University Press, Cambridge, 1995.

3 J. D. Kirkpatrick, I. N. Reid, J. Liebert, R. M. Cutri, B. Nelson, C.Beichman, C. C. Dahn, D. G. Monet, J. E. Gizis, and M. F. Skrutskie,Astrophys. J. 519, 802 1999.

4 A. J. Merer, Annu. Rev. Phys. Chem. 40, 407 1989.5 P. F. Bernath, Transition Metal Monohydrides, in Advances in Metal

and Semiconductor Clusters, Vol. 5, edited by M. Duncan Elsevier, NewYork, 2001.

6 W. J. Balfour, C. X. W. Qian, and C. Zhou, J. Chem. Phys. 106, 43831997, and references therein.

7 R. S. Ram and P. F. Bernath, J. Mol. Spectrosc. 184, 401 1997, andreferences therein.

8 T. M. Dunn private communication.9 D. Iacocca, A. Chatalic, P. Deschamps, and G. Pannetier, C. R. Acad. Sci.

Paris C 271, 669 1970.

10 W. E. Jones and G. Krishnamurty, J. Phys. B 13, 3375 1980.11 R. S. Ram, P. F. Bernath, and S. P. Davis, J. Chem. Phys. 114, 44572001.

12 A. S. Averyanov and Y. G. Khait, Opt. Spectrosc. 67, 829 1990.13 J. F. Harrison, private communication.14 P. J. Bruna, private communication; J. Anglada, P. J. Bruna, and S.

Peyerimhoffunpublished.15 R. B. LeBlanc, J. B. White, and P. F. Bernath, J. Mol. Spectrosc. 164, 5741994.

16 R. S. Ram, J. R. D. Peers, Y. Teng, A. G. Adam, A. Muntianu, P. F.

Bernath, and S. P. Davis, J. Mol. Spectrosc. 184, 186 1997.17 R. S. Ram and P. F. Bernath, J. Mol. Spectrosc. 186, 113 1997.18 J. Anglada, P. J. Bruna, and S. D. Peyerimhoff, Mol. Phys. 69, 281 1990.19 R. S. Ram, A. G. Adam, A. Tsouli, J. Lievin, and P. F. Bernath, J. Mol.

Spectrosc. 202, 116 2000.20 R. S. Ram and P. F. Bernath, J. Chem. Phys. 101, 74 1994.21 M. A. Lebeault-Dorget, C. Effantin, A. Bernard, J. DIncan, J. Chevaleyre,

and E. A. Shenayavskaya, J. Mol. Spectrosc. 163, 276 1994.22 E. A. Shenayavskaya, M. A. Lebeault-Dorget, C. Effantin, J. DIncan, A.

Bernard, and J. Verges, J. Mol. Spectrosc. 171, 309 1995.23 R. S. Ram and P. F. Bernath, J. Chem. Phys. 105, 2668 1996.24 R. S. Ram and P. F. Bernath, J. Mol. Spectrosc. 183, 263 1997.25 R. S. Ram and P. F. Bernath unpublished.26 J. M. Brown, A. S.-C. Cheung, and A. J. Merer, J. Mol. Spectrosc. 124,

464 1987.27 See EPAPS Document No. E. JCPSA6-116-003217 for the observed line

positions in the near infrared system of VF. This document may be re-trieved via the EPAPS homepage http://www.aip.org/pubservs/epaps.html or from ftp.aip.org in the directory /epaps/. See the EPAPShomepage for more information.

28 R. S. Ram, J. Lievin, P. F. Bernath, and S. P. Davis unpublished.29 C. E. Moore, Atomic Energy levels USGPO, Washington, D.C., 1971,

Vol. 1, NSRDS-NBS 35.

7039J. Chem. Phys., Vol. 116, No. 16, 22 April 2002 Emission spectroscopy of VF


r. s. ram et al- infrared emission spectroscopy of the [10.5]^5-delta-x^5-delta system of vf

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