r.s. ram et al- the a^2-pi-i-x^2-sigma^+ system of cp: observation of new bands

8/2/2019 R.S. Ram et al- The A^2-Pi-i-X^2-Sigma^+ System of CP: Observation of New Bands

1/12

JOURNAL OF MOLECULAR SPECTROSCOPY 1 5 2 , 8 9 - 1 0 0 ( 1 9 9 2 )

The A *l-Ii-X *Z+ System of CP: Observation of New BandsR. S. RAM, S. TAM, AND P. F. BERNATH *,*

Departm ent of Chemist ry, University of Arizon a, Tucson, Arizon a 85 721

Infrared emission spectra of the A&X*Z+ system of CP have been observed at high resolutionusing a Fourier transform infrared spectrometer. The rotational structure of seven new bandsinvolving vibrational levels up to u = 4 of both electronic states has been analyzed and equilibriummolecular constants have been determined. For the X*Z+ state o, = 1239.77924( 8) cm- and r,= 1.5619780(2) 8, were derived, while for the A*& state the corresponding values are w, =1062.47140(98) cm- and r, = 1.654420(6) A. o 1992Academic press. IN.

INTRODUCTIONCP is a free radical isovalent with CN and SIN. This radical was first observed by

Herzberg ( 1) who observed the B2Z +-X22 + transition which is analogous to theviolet system of CN. The rotational structure of this system was analyzed by Baerwaldet al. (2), who also observed the B2Z+-A*II transition. The rotational structure ofthe B2Z+-A 211system was also investigated by Chaudhry and Upadhya (3) and laterby Tripathi et al. (4).

More recently we reported the first observation of the A *Hi-X 22 +transition of CP(5) (analogous to the red system of CN). In this study the rotational analysis of fivevibrational bands was carried out. This work was followed by the detection of thepure rotational spectrum in the ground electronic state of CP by Saito and co-workers(6). These microwave measurements resolved the hyperfine structure due to the Pnucleus (I = 1) . Calculations of Franck-Condon factors, r-centroids, and the potentialenergy curves of CP have been published by several workers ( 7-20).

CP is an excellent candidate for detection in circumstellar envelopes of stars (suchas IRC + 102 16) and in the interstellar medium. IRC + 10216 is a prototypical coolcarbon star surrounded by a thick shell of dust and molecules. Linear carbon chainmolecules such as C, (11, 12), C,H (13), C,N (14), C,O (15), C,S (16, 27), andHC,N ( 28, 19) have been found in IRC + 102 16 and various other extraterrestrialsources, suggesting that the analogous phosphorous families C,P and HC,P might befound. CP is the first member of the C,P family.There is a surprisingly strong bond in the CP molecule with a large dissociationenergy of 12 1 kcal/ mole (20-22). This large dissociation energy also makes the de-tection of CP quite favorable in space. These speculations have recently been confirmedby the observation of CP in the carbon star IRC + 102 16 (23). Other recent work onCP includes the detection of the ESR spectrum in an argon matrix and two ab initiocalculations of molecular properties (24, 2.5 .In the present study we extend our previous work on the A211i-X*Z+ transition ofCP to include bands involving v = O-4 of both states. We have rotationally analyzed

Camille and Henry Dreyfus Teacher-Scholar.* Also: Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G 1.8 9 0 0 2 2 - 2 8 5 2 1 9 2 $ 3 . 0 0

Copyright 0 1992 by Academc Press, Inc.All rights of reproduction in any form reserved.


2/12

90 RAM, TAM, AND BERNATHTABLE I

Observed Wavenumbers of the Lines in the New A-X Bands of CP

8.59.5

10.511.512.513.514.515.516.517.518.519.520.521.522.523.524.5z5.526.527.528.529.530.531.532.533.534.535.536.537.538.539.5

6454.6190 -76452.2395 -1,6449.6827 -76444.0354 66440.9446 116d37.6736 -76434.230, 3064306030 106426.7975 -176418.6627 266414.3214 -27

J R2

2-2 BAND

6356.6099 76350.5571 4463443w7 -3o-c QZ

6456.1YR 536455.4059 -46454.5076 -146453.4325 -146452.17% -146450.74% -56449.,4,4 -L6447.3572 226445.3909 16443.2497 8644c.9294 26438.4322 36435.7568 -26432mn 346429.8765 20w?6..%74 4t423.2793 -28

6407.9694 -26403.7017 326399.2519 156394.6243 -1063am2.50 176384.8451 66379.6886 -46374.3523 -4563688487 763573028 186351.2593 -37

o-c P21 o-c Q21 o-c

6449.3829 -396447.6330 -96445.7028 -56443.5954 56441.3117 286438.8448 -36436.2037 -16433.3841 -86430.3459 146427.2155 86423.8635 I6420.3358 106416.6265 -2.56412.7170 I16108.6862 56404.44go 66400.0347 66395.4420 .96390.6739 -106383.7265 -366380.6113 27637.5.3c98 -76369.8360 06364.1861 II6358.3572 463323549 66346.1762 146339.8195 36333.2868 -106326.5811 66319.6982 663126430 396305.4103 516297.5-Z, 46290.4088 -266282.6515 -4

3.54.5

16.5 66m4217*7.5 6598.1509L8.5 6595.715819.5 6593.115220.5 6590.347321.5 6587.413122.5 658434m23s 6581.043524.5 6577.61,325.5 6374.017526.5 6570.245827.5 6566.315328.5 6566zZL7229.5 6557.952030.5 6553.522331.5 6548.926532.5 6344.162833.534.535.5x537.538.539.5

6575.63796571.39936365.99486562.423212 6s7.6925

5 63527935-7 6547.7276-1 6.542.M,2II 6337.104711 6331.551410 a23.8265

-34 6519.9363-19 6x3.8&13-13 6307.665739 6501.2838

-2.4-12-12-20

-79

11

2-2 BAND CONTINE! J6.508.4751 96606.9b94 -46&n.25&5 -,26603.404, -1MoI.3446 146599.1997 2963%.84X 266594.3258 -,6

13 6591.6453 715 6588.7976 1310 6585.7835 10

-17 65826037 316 6579.2570 -191s 6575.7497 8-5 657m743 718 6568.2329 1

-II 6564.226% 146 6560.053, -2,23 6355.7186 3

1 m1.2,,7 -24 6555.29967 6546.5489 4 6550.7826

-5 6341.7153 -2 6s&og66-4 65367159 -13 6x1.2462

6531.5514 -22 6536.22636526.2247 L 653LWS96520.7300 .2 6525.697965L5.0107 2 6.52c.18946509.2456 1 6514.m6503.2556 5 6508.66516497.0995 1 6502.6604649).n95 II6484.2920 -16477.6408 36470.822, -146463.8414 L64566934 -36449.3829 20

[email protected].%2,6an.175366m2192CYBl.lU206597.80896595.3343659273846.5X.9477

-37 6_58699710 6583.88151 6580.5930

II-16

-1-914147

48


3/12

CP A2n,-X*Z+

TABLE I-Continued

-242844

-3454244

-26233.5LO24

6425.3464 -8-

seven new bands, 2-2, 3-3, 3-1, 1-3, 2-0, 4-3, and 2-4. The molecular constantsobtained in this study, combined with our previous data, provide improved equilibriumconstants for both electronic states. These constants were used in the calculation ofpotential energy curves for the A II and X 2Z + states and the Franck-Condon factorsfor the A-X system.


4/12

92 RAM, TAM, AND BERNATHTABLE I-Continued

4.55.56.57.58.59.5

10.5II.512.513.514.515.516.517.518.519.520.521.522.523.524.525.526.527.528.529.530.531.532.533.534.535.536.537.528.539.5 4m.5265 3

J RZ Q-C PZ Q-C QZ o-c RZ1 Q-C P21 o-c Q21 Q-C

2.53.54.55.56.57.58.59.5

10.511.512.513.514.515.516.517.518.519.520.521.522.523.524.525.526.527.528.5 -

EXPERIMENTAL DETAILSThe emission spectra of CP were observed in two separate experiments. In the firstspectrum (used in the previous analysis) CP bands were observed in a microwave

discharge of a mixture of 0.04 Torr of white phosphorous vapor and 0.4 Torr of H2in a quartz cell. This cell was previously used in experiments with methane so the


5/12

CP A*&X*X+

TABLE I-Continued93

0.51.52.53.54.55.56.57.58.59.5

10.511.512.513514515.516.517.518.519.520.521.522.523.524.525.526.527.528.529.530.531.532.533.534.535.536.537.5

8895.65308895.55598895.2430889d.03198593.1156m m 5 58890.687,

-1549

-2726

-263

-27-23-13-2042423

-10

8%9.17,48B7.45398885.53288883.41228881.09*16878.56548m5.83478872.90688869.77608866.44378862.9M9Fa59.17598855.2387Fa5LlOIO8846.7626884~21728837.4780

-2-3210

5915

-28883253566827.38718a22.04498816.49708810.7459sax80338798.658187VL304487S.75248779.0104

8878.0565 -558674.5742 -18870.8846 -58866.w44 -188629069 44m58.6084 -88854.1132 -158849.4191 08844.5215 -98839.4246 -28834.1255 a6828.6239 -3,8822.926* II8817.m4 -18810.91% -59e&x6213 -2687ps.1192 -328,9,.4,%5 -218784.5203 16sm .4157 -,I877o.,,cc3 4467626134 -46754.91M -268w.0135 IIsn8.5w.l -458730.6144 8Km.1155 08713.4165 -19869S.4316 368686.1359 108676.6445 12e-%5.%99 -368657.06u -33

8890.7934 338889.2945 -258881.M18 -38885.7050 -48883.&w -27&x31.3031 **88B.m 398876.1003 -138873.1972 7.smo.w24 248866.7818 -I8863.2720 -38859.5605 -98855.w3 -488851.5364 98847.220, -68842.7M5 -38837.9868 -108833.0x5 88822954 4088226295 -148817.1015 -2888LL.3896 ,88n5.4688 188799.3440 -58,93.@210 -58786.4995 138779.7740 -78,7,X01 -88765.7273 28,58.403* -18750.8815 19Sm .1550 -126735.2301 -30*7.,100 -4r7187869 -148110.2654 -148.5 8825.9101 32 8,18.0724 -1039.5 882O.lm5 -4 8709.5343 9 676&1695 -12 8701.5457 -4

J RZ Q-C P2 0-C QZ 0-C RZL 0-C P ZL 0-C QZ I Q-C

2.53.54.55.56.57.58.59.5

10.511.512.513.514.525.516.517.518.519.520.5x522.523.524.525526.527528.529.530.531.532.533.534.535.5

9051.0907 -59350.0968 -245048.9202 299047.5437 -209095.9822 -209044.2403 75

9037.*392 29035.3298 2190326296 329029.7338 -1290266557 229023.3841 239016270, 22

9035.6689 -3790322566 -65028.6549 249w24.8558 -2s9020.8748 d9016.697, -54m2.3411 -5!xm7.7870 -41vYl3.0525 118998,231 3gglj.0052 88987.6946 -3989821!?m -39SZ76.5163 -228970.6439 -138964.5862 328951.8925 28945.2589 49m38.4477 116931.4444 378924.2483 228916.8580 498909.2907 -3Sm.5281 -258893.5784 -32a85.4404 -3,8877.1221 408868.6044 78a59.8999 -8s851.0065 -31

7.6 BAND CONTINUED9048.2612 -309046.8LlS 249045.1640 -11YM3.3295 -189u41.M6 0 .*o9039.0985 339X.5.6926 4w34.1014 1mu*59 -429ma)491 -590LS.1872 -249uz1.8425 239318.2989 -249014.5701 279010.6551 -350X.5459 -255mI2482 -378997.7,15 5489B.091, 9m88.m 388983.1728 68977.9268 -1989724978 L98966.8758 216%l.M26 58955.0588 238948.868, -1989424936 288935.9201 -158929.,661 3189222145 -56915.0771 -48w7.7481 -268900.2342 -2

9x0.7403 429061.8759 -139w3.59409064.16219X4.5478

55 9041.17352980 w6s138

9033.91129031.3658wzs.120593X%)4169021.57%9014.*,17 509010.3276 299io6.2033 .I69001.8914 1589!n.3921 65m.6ssO -36

48-2849

2312787

mQ.9303 -305M9.9272 44m48.7253 299047.32% -269045.7528 7*3.9%11 499342.0219 169039.8687 -379037.5304 -225ll35.mna 209032.2,81 -489029.3732 39X6.2764 359022.9831 39019.4979 43m5.8310 -65011.9740 33San.9202 79003.678-J 989.X.6254 158989.8096 -16


6/12

94 RAM, TAM, AND BERNATHTABLE I-Continued

J R2 Q-C P2 Q-C Q2 Q-C R21 Q-C PZ, 0-c Q2, Q-C

556.57.58.59.5

10511.512.513.514.515.5L6.517.518.519.520.521.522.523.524.525.526.527.528.529.530.531.532.533.534.535.536.537.538.5 8677.3999 -19

J Rl Q-C F-1 Q-C Ql Q-C RI* Q-C P,2 Q-C Ql2 Q-C

3.54.5556.57.58.59.5

10.511.512.513.514.515.516.517.518519.520.521.522.523.524.525.526.527.528.529.530.531.532.533.534.535.536.537.5 7190.680, -3638.5 7,84.22,6 5


7/12

CP A2rI,-xZZ+

TABLE I-Continued95

J 01 cl-c RI2 Q-C Q12 Q-C

carbon atoms required for the formation of CP were deposited on the walls of thedischarge cell. This experiment was originally designed to produce the vibration-rotation bands of PH (26). In the second spectrum (used in this analysis) a mixtureof 0.04 Tot-r of white phosphorous vapor, 2.75 Torr of He, and 0.03 Torr of CH4 wasused in the same discharge tube. The spectra obtained in these experiments wereextremely rich with strong spectra of CP (5), CH (2 7, 28)) PH (26), P2, CN, C2 (29,JO), and C, (31).

In fact, the new bands of CP were noticed because of the presence of the 2-2 bandnear the C3 triplet system (31). The emission from the discharge was focused on theentrance aperture of the McMath Fourier transform spectrometer of the NationalSolar Observatory at Kitt Peak. InSb detectors and silicon filters limited the band passto the 1800-9000 cm- spectral region. An unapodized resolution of 0.02 cm- wasused in these experiments. A total of 10 and 9 scans were co-added, respectively, in70 and 65 min of integration. The spectra were calibrated using the measurements ofthe vibration-rotation lines of CO (32) impurity present in the spectra. The absoluteaccuracy of the calibration is estimated to be better than +O.OO cm- .

RESULTS AND DISCUSSION

The spectral line positions were extracted from the spectra using the data reductionprogram PC-DECOMP developed at Kitt Peak by J. Brault. The peak positions werefound by fitting a Voigt lineshape function to each feature using a nonlinear least-squares procedure. Since the spectra are very congested, we proceeded by initiallypredicting the line positions and then picking out and assigning just a few lines. Thepreliminary fit of these lines provided an accurate prediction of the remaining lines.The search for new bands involving the higher vibrational levels in both the stateswas guided by a preliminary Franck-Condon calculation.

The seven new bands identified and analyzed in the present study are 2-2, 3-3, 2-0, 3-1, l-3,4-3, 2-4. The structure of 4-3 and 2-4 bands is very weak so the 2111,2-


8/12

96 RAM, TAM, AND BERNATHTABLE II

Hyp erfme-Free Pure Rotational Transition s of CP (in cm-)

N-N J- 1 v(Correeted)

2-l 2.5-1.5 3.19276644(121)2-l 1.5-0.5 3.17420027(229)3-2 3.5-2.5 4.784426359(88)3-2 2.5-1.5 4.76585910(-5)5-4 5.5-4.5 7.96743092(10)54 4.5-3.5 7.94886265(43)b-5 6.5-5.5 9.55870811(-47)b -5 5.5-4.5 9.54014160(27)7-b 7.5-6.5 11.14979550(-54)7-b 6.5-5.5 11.13122800(-79)

*Z+ subbands could not be identified with certainty. The assignment of the new bandswas straightforward using combination differences and estimates of the rotationalconstants for the higher vibrational levels based on the data provided in our previousstudy (5). The observed line positions and their rotational assignments are providedin Table I.

Initially, band-by-band fits ofthe line positions listed in Table I were made utilizingthe effective Hamiltonian of Brown et al. (33). Matrix elements for this Hamiltonianare listed by Amiot et a l. (34) for *II states and Douay et al. (35) for *2 states. In thefinal fit the observed transition wavenumbers of all the bands, together with the hy-pet-fine-free pure rotational transition wavenumbers (Table II) were fitted to determinethe molecular constants provided in Tables III and IV. The pure rotational transitionfrequencies provided by Saito et al. (6) were corrected for the effects of hyperhnestructure so that they could be introduced directly into our fits. For the 4-3 band theconstants Ad, AD.+, nd q4 were fixed to extrapolated values, since the *II, ,2-22 + sub-band involving the o = 4 level was not measured.

The constants of Tables III and IV were utilized to determine the equilibriumconstants in both electronic states using the expressions

G(u) = w,(z) + 4) - w,x,(v + f) + w,y,(u + f)B = B -c+++)+~(u+f)*.e e e

TABLE IIIMolecular Constan ts for the X 22 + State of CP (in cm- ; One Standard Deviation in Parentheses)

constant v=o V=l v=2 v=3 v=4

T 0.0 1226.12726(21) 2438.57459(u)) 3637.33379(26) 4822.3965(10)B 0.795881@2(3) 0.78989532(59) 0.78389287(65) 0.77787438(98) 0.7718384(84)l&D. 1.32794(29) 1.33169(40) 1.33620(47) 1.34310(76) 1.347( 15)1okY 1.8567250(27) 1.849675(56) 1.844718(60) 1.839951(75) 1.83215(57)


9/12

CP A211i-X2Z+ 97TABLE IV

Molecular Constan ts for the A211i State of CP (in cm- ; one standa rd deviation in parent heses)

Constan t v=o v=l v=2 v=3 v=4

T 6884.00555(15) 7934.41442(17) 8972.76553(21) 9999.06509(26) 11013.31730(50)A -156.24385(16) -156.12670(23) -156.04318(28) -156.01186(27) -156.0513=

I@% Am 4.868( 18) 4.269(32) 3.022(46) 0.534(48) 0.534B 0.70927628(42) 0.70364924(50) 0.69801488(70) 0.69237961(90) 0.6867240(20)

10%D, 1.28046(34) 1.28306(38) 1.28519(56) 1.28964(66) 1.2937( 16)1ol p. 9.414(14) 9.442( 18) 9.655(29) 10.175(14) 14.3(13)l@x 9. -4.797(67) -4.873(93) -4.886(9) -4.94( 11) -4.94=

10% pDr -1.28(11) -1.04(16) -l&4(36) -1.04 -1.04=

a Fixed values; see text.TABLE V

Equilibrium Vibrational and Rotational Constants for the X2,2+ and A211i States of CP (in cm-)

Constant

% 123979924(8) 1062.47140(98)we 6.833769(46) 6.03277(50)

lh w. -0.13769(72) 0.0897(72)B, 0.798867748(82) 0.7120871(26)

10% cz, 0.596933(19) 0.56203(34)lox Y. -0.8229(56) -0.323(83)

r , 1.5619780(2) 1.654420(7$

TABLE VITurning Points of the RKR Potential Energy Curve of the A211, State of CP

V E(v) (cm-) r- (18) r- (%

1.71841.7471

0.00.51.01.52.02.53.03.54.0

7502.20598028.91818552.61499073.29719590.9658

10105.621610617.265711125.898711631.5216

1.59701.57501.55871.54541.53401.52391.51491.50661.4990

1.77001.79001.80811.82501.84081.85591.8704

5.0 12633.7407 1.4853 1.8980

a Calculated relative to the minimum of the X22 + potential curve of the value of cm-.


10/12

98 RAM, TAM, AND BERNATH

TABLE VIITur ning Points of th e RKR Potent ial Ener gy Cur ve of th e XZ+ Stat e of CP

E(v) (cm) rmb 2) r, (X)0.0 618.2003 1.5087 1.62110 . 5 1232.9734 1.4882 1.64761.0 1844.3276 1.4731 1.66871.5 2452.2618 1.4607 1.68712.0 3056.7749 1.4501 1.70382.5 3657.8661 1.4407 1.71933.0 4255.5341 1.4322 1.73393.5 4849.7781 1.4245 1.74774.0 5440.5969 1.4174 1.76105.0 6611.9549 1.4046 1.7863

The final equilibrium constants thus obtained are provided in Table V. These constantswere used as input to an RKR program to calculate the classical turning points of theA *Iii and X *JZ+potential energy curves (Tables VI and VII). Figure 1 is a plot of thepotential energy curves of the A *Iii and X *2 + states of CP.

The RKR potential curves were used to calculate the Franck-Condon factors forthe A *Iii-X *Z + system (Table VIII). The observed relative intensity of various bandsfollows the predictions based on the Franck-Condon factors. The values of BL andBE esult in r, values of 1.5619780(2) and 1.654421(7) A for X*Z+ and A*& states,respectively.

The inclusion of the hyperfine-free microwave transition frequencies in our fitsresults in a very precise determination of the rotational constants in the ground vi-brational state. The pure rotational transitions also help break correlations betweenconstants of the A*II and X22+ states. The constants provided in Tables II and IIIare in good agreement with the constants obtained in our previous study, except forv = 3, because only the *I13,*-*Z+ subband of the 3-l band was included in theprevious analysis.

TABLE VIIIFr an ck-Condon Factors for th e A%-X*Z+ System of CP

v 0 1 2 3 490 0.2835EO 0.3907EO 0.231OEO 0.7680E-1 O.l581E-11 0.3240EO O.l884E-1 0.1352EO 0.2845EO 0.1743EO2 0.2134EO 0.6721E-1 0.1478EO 0.414OE-2 0.1988EO3 0.107OEO 0.17OOEO 0.241 E-2 0.1489EO 0.2849E-14 0.4548E-1 0.1601EO 0.5411E-1 0.6174E-1 0.6946E-1


11/12

CP A2&X2Z+ 99

FIG. 1 . Potential energy curves for the A%, and X Z:+ electronic states of CP.

ACKNOWLEDGMENTSWe thank R. Hubbard, J. Wagner, and G. Ladd for assistance in acquiring the CP spectra. The National

Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc., undercontract with the National Science Foundation. Acknowledgment is made to the donors of the PetroleumResearch Fund, administered by the American Chemical Society for partial support of this work. Somesupport was also provided by the Natural Sciences and Engineering Research Council of Canada and theNASA Origins of the Solar System Program.

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r.s. ram et al- the a^2-pi-i-x^2-sigma^+ system of cp: observation of new bands

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