r.a. hailey et al- the b^2-sigma^+-x^2-sigma^+ transition of caod

8/2/2019 R.A. Hailey et al- The B^2-Sigma^+-X^2-Sigma^+ Transition of CaOD

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JOURNAL OF MOLECULAR SPECTROSCOPY 147,40-45 (1991)

The ~?Z--~ 2Z+ Transition of CaODR. A. HAILEY, C. N. JARMAN, W. T. M. L. FERNANDO, AND P. F. BERNATH

Depurtment of Chemistry . Universit), of Arizmu. Tucson, Arizonu 85721

The iS+-,?S+ transition of CaOD near 5550 A was studied using dye laser excitationspectroscopy.The OOO-OOO band was rotationally analyzed and r. structures were established forboth states. For the BS+ state the following bond lengths were found: rc._o = 1.9697 8, andrO_ = 0.9179 A, while for the /;*Z+ state rc.-o - I .%49A and rO- = 0.9207 A. 0 1991 AcademicPress. Inc.

INTRODUCTIONThe spectra of CaOH are well known because when calcium salts are added to

flames, the reddish and greenish emission of CaOH is observed ( 1, 2). The red emissionnear 6220-6270 A belongs to the &I-J?22+ system, while the green emission near5550 A corresponds to the j22-j Z+ transition (2). Hilborn et al. (3) rotationallyanalyzed the OOO-OOOband of the A211-J?22+ transition for both CaOH and CaOD.Bernath and Kinsey-Nielsen (4) analyzed the 822+-.?22 transition of CaOH, whileBernath and Brazier (5) measured some additional k211-2X+ lines and fitted the A-J? and g-2 data together.

The initial goal of our work was to investigate the highly excited electronic statesof CaOH using the technique of optical-optical double resonance. Many new vibronicstates were found during the course of our research, but it was necessary to differentiatethe origin bands from vibrationally excited bands by using isotopic substitution. Whilethe rotational analysis for the OOO-OOOband of the 8Z-iZ+ transition of CaOHis complete (4), the corresponding CaOD transition had not been analyzed. Conse-quently it was necessary to record the high-resolution spectrum of the green systemof CaOD to aid in our optical-optical double resonance assignments. This paper con-tains the rotational analysis of the OOO-OOOband of #21;f-22Zt transition of CaOD,as well as r. structures for both states.

EXPERIMENTAL DETAILSThe CaOD was produced in a Broida-type oven (6) by the reaction of Ca metal

vapor and 0202. It was found that the D202 produced more CaOD than D20 in thereaction with ground state ( So) Ca vapor. The calcium was vaporized in a resistivelyheated alumina crucible and a flow of argon carried the Ca atoms from the crucibleto the reaction region. In order to get sufficient D202 partial pressure inside of theoven, argon was bubbled through the oxidant. The pumping speed and the flow rate

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&,f OF CaODTABLE I

Measured Line Positions of the 000-000 Band of the j2S(in cm- )+

4

?S+, Electronic Transition of CaOD

N Pl 0-ca P? o-c 5 o-c R2 0-t:

i45678'210111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364

18013.?90 218012 664 -718012.063 1118011.462 -118010.874 118010.290 -118009.721 218009.160 418008 604 218008.059 318007 515 -518006.987 -618006.477 218005.970 418005 467 118004.974 -118004.493 018004.018 -218003.556 018003.101 018002.662 718002.219 118001.791 018001.371 -118000.961 -218000.549 -1218000.170 017999.789 117999.411 -417999.048 -217998.696 117998.348 -117998.009 -217997.685 217997.363 -117997.055 117996.751 -117996.459 -217996.177 017995.905 217995.644 617995.387 617995.136 117994.898 217994.666 -217994.446 -117994.236 017994.030 -317993.835 -517993.654 -117993.478 -217993.313 017993.158 317993.009 317992.867 017992.739 317992.613 -117992.503 317992.399 317992 299 -117992.210 -317992.135 017992.065 -117992.004 -1

18012.738 510812.183 1718011.605 -118011.056 -118010.516 018009.982 -218009.460 -118008.950 318008.444 118007.947 018007.459 -118006.987 518006.512 -218006.056 218005.605 118005.162 018004.730 018004.306 -118003.893 118003.491 418003.093 218002.700 -318002.322 -418001.954 -218001.594 -318001.248 218000.909 518000.584 1318000.244 -317999.932 017999.621 -617999.329 017999.043 117998.764 117998.492 -217998.234 117997.987 517997.738 -117997.503 -317997 281 017997.062 -317996.857 -217996.661 017996.467 -517996.292 017996.123 117995.960 017995.809 217995.663 017995.526 -217995.394 -717995.290 517995.161 -1617995.080 317994.988 1

18014.491 118015.096 218015.701 -518016.325 -318016.964 618017.598 118018.247 118018.902 -118019.570 018020.246 118020.929 018021.628 718022.323 018023.023 -1018023.757 418024.477 -418025.216 -218025.974 1118026.712 -618027.478 -318028.254 018029.026 -818029.820 -418030.620 -218031.434 418032.244 -118033.070 118033.899 -318034.742 -118035.596 318036.451 -118037.317 -218038.203 818039.080 018039.974 118040.872 -218041.779 -518042.699 -418043.628 -218044.565 018045.511 218046.444 -1718047.436 1518048.393 318049 368 118050.350 -218051.351 418052.348 018053.359 118054.376 -118055 387 -16

18015.192 -218015 838 -918016.505 -418017 182 218017 864 318018.547 -218019.225 -2118019.954 018020.669 -118021.393 -118022.129 218022.869 018023.619 -118024.384 418025.149 018025.921 -518026.712 -118027.506 -218028.305 -718029.134 1018029.949 418030.777 218031.613 -118032.458 -418033.319 018034.190 718035.054 -218035.937 -218036.831 118037 729 118038.635 -118039.550 -318040.489 1118041.414 218042.353 018043.301 -218044.269 618045.229 -118046.210 418047.190 018048.184 1lEO49,lEO -418050.192 -1

a O-C corresponds to the observed minus calculated pasitians(in 103cm 1)usingthe spectroscopic constants in Table II.


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42 HAILEY ET AL.

64 62 60 66 56 54 52 s(N)

17692 17993 cm-

FIG. I, High-resolution CaOD spectrum. This is a section of the laser excitation spectrum of the P, branchof the OOO-OOO band of the BS+-jZ t ransition. The P, branch forms a head at I7 99 I.828 cm-.

were adjusted to optimize the signal. The total pressure in the oven was -7 Torr( mostly argon and a few mTorr D202 ) .

Dz02 was made by the deuteration of 30% HZ02. First the excess water was pumpedoff and then 99.9% D20 was added to the Hz02. After deuteration, the mixture wasconcentrated by pumping off the excess water. This procedure was repeated severaltimes.

The laser used in this experiment was a single-frequency Coherent 699-29 ring dyelaser pumped by a Coherent Innova 20 argon ion laser (SW). The dye laser wasoperated with Rhodamine 110 dye. The laser beam was focused horizontally into theflame. Spectra were obtained by scanning the computer controlled ring dye laser whiledetecting the total fluorescence with a photomultiplier tube. The wavemeter of thering dye laser was calibrated by simultaneously recording an excitation spectrum iodinevapor ( 7). The line positions have been corrected by the subtraction of 0.0056 cm-(8). The measured CaOD lines are listed in Table I. The estimated accuracy of theline positions is kO.004 cm-.

RESULTS AND DISCUSSIONA portion of the laser excitation spectrum of the 88-A?2 transition of CaOD

near the P, head of the OOO-OOOband is shown in Fig. 1. Each 2 state has two spincomponents [F1 (e) and Fz(f)] and therefore the X+-S+ transition consists of fourbranches, PI, Pz, RI, and Rz at high N ( 9). The P branches form heads at 17 99 1.828and 17 994.554 cm-, for the F, and F2 spin components, respectively. Because the2 and 2 state potential curves are very similar the band heads occur at very high N(N = 70 for PI and N = 66 for P?). The R branch region of the spectrum containsmany vibrational sequence bands as well as the R, and R2 branches of the OOO-OOOband. In order to analyze these sequence bands the technique of laser excitation spec-troscopy with filtered fluorescence detection must be used.

The rotational lines of the P, and PZ branches were easy to pick out, but becauseof the many interfering lines present in the R branch region it was difficult to pick


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&,? OF CaOD 43TABLE II

Molecular Constants for CaOD f?\+ and x% States (in cm-)

a One 0 uncertainty in parenthesesbFixed to the value calculated from the isotopic relationship (see

out the R-branch rotational lines. The rotational assignments were made by first pre-dicting the spectrum using an estimated band origin and molecular constants. Theinitial estimates were made using the previous work for CaOD (3) and CaOH ( 3 ).Then the band origin was changed until the positions of the P heads, as well as thepattern of the R rotational lines in the predicted spectrum. matched the actual linepositions.

The lines were fit to the Z energy level expression using a nonlinear least-squaresprogram. The Hunds case (a) matrix elements of the standard IX Hamiltonian ( JO)used in this analysis are listed in the paper by Douay ef al. ( I1 ). Only y- y is welldetermined, therefore for the final fit y was fixed to the value obtained using theisotopic relationship

BCaODYCaOD = -fCaOH r .

CaOH(1)

&OH and Y&OH were taken from the results of Bernath and Brazier ( 5). The molecularconstants from the final fit are presented in Table II.The accuracy of Eq. ( 1) can be checked by substituting the 7kaon from this workinto Eq. ( 1 ), and predicting the -y&on value (-0.043 640 cm-). This value is identical,within experimental error. to the result from Bernath and Brazier ( -0.0436 15( 46 )

TABLE IIIBond Lengths in CaOH and CaOD ( in &)

Bond length x++ SC+

ro(Ca-0) 1.9849 1.9697r&O-B) 0.9207 0.9179


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44 HAILEY ET AL.TABLE IV

Ground State Bond Lengths for the Alkaline Earth Monohydroxides (in A)BondLength MgOHa caoH SrOHC BaOHd

ro(M-0) 1.770 1.984 2.111 2.201r,(O-H) 0 912 0.921 0.922 0.923

a Reference 12. This work.c Reference 13.d Reference 14.

cm-) (5). The ground state constants are in reasonable agreement with those ofHilborn et al. (3).

CaOH and CaOD are linear. Using the relationship between the moment of inertiaand the bond lengths of a linear molecule

I = ~(rn,m,r?, + mlm3& + m2m3r&) (2)the r. structures for CaOH in both the BS and J?Z+ states were determined. Themoments of inertia for CaOD are calculated from the B values of Table II, while thecorresponding data for CaOH were taken from the work of Bernath and Brazier (5 ).The results are presented in Table III. The bond lengths of the B2Zf state are shorterthan in the 22 state which suggests that the nonbonding valence electron has slightantibonding character in the ground state.

For the x22+ state the Ca-0 bond length ( 1.985 A) agrees with the value of Hilbomet al. (3), but the ground state O-H bond length (0.921 A) is different than theirvalue (0.901 A). This difference reflects the slightly different B values used in ouranalysis, and we note that r. structures for hydrogen atom positions are notoriouslyunreliable. However, the O-H bond length obtained in this work compares quite wellwith the O-H bond lengths found in the other alkaline earth monohydroxides. Theknown bond lengths of the ground states of the alkaline earth hydroxides are providedin Table IV for comparison purposes.

ACKNOWLEDGMENTThis work was supported by the National Science Foundation (CHE-89 13785 )

RECEIVED: November 26. 1990REFERENCES

1. J. F. W. HERSCHEL, Trans. R. Sot. Edinburgh 9,445-460 ( 1823).2. C. G. J AMES AND T. M. SUGDEN, Nature (London) 175, 333-334 (1955).3. R. C. HILBORN, Q. ZHU. AND D. 0. HARRIS, J. Mol. Spectrosc. 97, 73-91 ( 1983).


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&.f OF CaOD 454. P. F. BERNATH ND S.KINSEY-NIELSEN.hem. Phys. Lett. 105,663-666 ( 1984).5. P. F. BERNATH ND C. R. BRAZIER.Astrophys. J. 288.373-376 ( 1985).6. J. B. WEST, R. S. BRADFORD, . D. EVERSOLE, ND C. R. JONES. Rev. Sci. Instrum. 46, 164-168

(1975).7. S. GERSTENKORNND P. Luc. Atlas du spectra dabsorption de la molecule diode. CNRS. Paris.1978.8. S. GERSTENKORNND P. Luc, Rev. Ph.vs. Appl. 14,791-796 ( 1979).Y. G. HERZBERG, Spectra of Diatomic Molecules, 2nd ed., Van Nostrand-Reinhold, New York, 1950.10. R. N. ZARE, A. L. SCHMELTEKOPF.W. J. HARR OP , AND D. L. ALBR ITT ON, 1. MO/. Sptctrusc. 46, 37-

66 ( 1973).Il. M. DOUAY, S. A. ROGE RS, AND P. F. BERNATH,Mol. Phvs. 64,425-436 ( 1988 ).12. Y. NI, Ph.D. thesis, University of California, Santa Barbara. 1986: and D. 0. Harris and T. C. Steimle.private communication.13. J. NAKAGAWA, R. F. WORMSBECHER,AND D. 0. HARR IS, J. Mol. Speclrosc. 97, 37-64 ( 1983 ).14. S. KINSEY-NIELSEN.C. R . BRAZIER, AND P. F . BER NATH. J. Chem. Phy.r. 84,698-708 ( 1986).

r.a. hailey et al- the b^2-sigma^+-x^2-sigma^+ transition of caod

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