Spectrum of dideuteroacetylene near 18.6 microns

JOURNAL

OF

MOLECULAR

SPECTROSCOPY

4,

327-334

(1972)

Spectrum of Dideuteroacetylene

Near

18.6 Microns

AGOSTINO BALDACCI, SERGIO GHERSETTI, AND S. C. HURLOCK’ Laboratorio de1 C.N.R. dei Composti de1 Carbonio Contenenti Eteroatomi, Ozzano Emilia and Istituti di Chimica Organica delle Universiti di Bologna e Venezia, Italy

AND I<. NARAHARI RAO Department

of Physics,

The Ohio State University,

ColuwLbus, Ohio

43210

The bands of dideuteroacetylene ((AD,) at 18.6 p have been recorded with a high-resolution vacuum infrared spectrograph equipped with a liquid-heliumcooled Ge:Cu detector. Analysis of the VI, fundamental and several “hot” bands observed in this region led to a determination of accurate values for some of the molecular parameters useful in the interpretation of the near infrared bands of this molecule. Finer details related to l-resonance effects have been observed and discussed. I. INTRODUCTION

This paper presents the results of new measurements of the CzDz absorption spectrum in the region of t’he v5 fundamental near 18.6 b. The measurements were undertaken to complement the large amount of internally consistent data which recently became available for 12CzD, as a result of high-resolution studies made in the region l-10 p (1, 2). These near-infrared measurements included several “hot” bands originating in the level (OOOO”l’), which is the upper state of the v5 band. Because of the symmetries and selection rules, an indirect determination of this level was not possible. Thus, there was a pressing need to have a precise direct determination of the (OOOO”ll) level both because of its own importance and because of the many other levels which can be determined from it. The four “hot” bands observed in the v5 region are also important because their upper states, most of which had not been observed previously (3), participate in strong vibrational rotational interactions. II. BASIC OBSERVATIONAL

DATA AND MOLECULAR CONSTANTS

The spectrum is reproduced in Fig. 1 and relevant experimental details are included in the figure title. The determination of the spectral positions, analysis 1 Current affiliation: Michigan 48823.

Department

of Physics, 327

Copyrigllt @

1972 by Academic

Press, Inc.

Michigan

State University,

East Lansing,

BALDACCI, ET AL.

32s

PI38

I I PI35 I PI34 PI36

I J P126A

PI25 PI28

1

~8

I

I I I

I

I

I

I I I

I I

1

PI16 I PI15 I I PI18 I I P118 I PlQ I I

PI34

I

I

I I

I

I PI31 PI30 PI33 I

I

PI24 PI21 PI24

I

PI2 PI11’ I I I

I

I

I

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I

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PI13 I

PI13 I P113 PI13

I

I

PI

I

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I Pi28

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I

PI16

F

“”

D

I P I !* A I I P!6 Ps4 E P17 Pi6 I I I PI8 PIS D PI11 I 19 PI@; I

FIG. 1. Reproduction of the spectrum of C&D2in the region of the ~6fundamental at 18.6 p. Path length 1.5 meters, pressure 2-3 Torr. The spectrum was recorded using a 3.5 meter focal length Littrow spectrograph equipped with a 40 grooves/mm 150 X 230 mm2 echelle and a liquid helium cooled Ge:Cu detector. The d assignments are indicated below the spectrum and the bands are identified as follows: A. VS;B. ZVSO - ~5 ; C. (~4 + ~5)” - Y:, ; D. [214 - Y& ; E. [2ps2- Y&j ; F. [(Ye+ rg)%- Y& . The notation B.C. has been used to signify band center. Two traces appearing one below the other in the same spectral region correspond to two different pressures of the sample.

J

P’5

PST I

1 PI2 I

PI7 P7 p1B

1

I

I

I R14 R16 I

I

I

I

RI5 Rl5

RI17 I RI19

l

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I

1

I

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1

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I

l

RI22

I

RI32 I

RI32 I

I

I I

I

I

I

RI24

I

B.lC. RIO I RI3 I RI4 RI5 B.C. BJC. B.IC.

I RIG RI5 ; C R’3

: F

RI9 I I I I I I RI 6 I RI12 I I I I I Rllk ; R112 I I I I I I RI19 I I RI10 I I I I I RI16 ’ RIB Rlll I I I RI15 D RI11 I I I RI15 ;

l

I I RI37

RI2

I

RI17 RI18 RI20 I RI16 RI17 RI17 RI16

133 I

~42

I PI1 B.K. R’l PI1 BJC. I PI4 I I PI3

RI23 1

I

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RI37 I I

I I

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I RI39

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R141R142

Figure 1 329

I

I

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R130 I I

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I

RlsQ t C D

l

I

RI3

RI31

RI3i R130

k c

D E F

BALDACCI,

330

ET AL.

of the data and evaluation of molecular constants were performed using techniques described previously (1). Table I summarizes the different molecular constants obtained in the present investigation. Identification of the band (OO01’11)2-(OO01’Oo) and the J assignments of its rotational structure may be considered somewhat tentative because in the case of the c-c subband the spectrum was resolved between P( 20) and R( 18) whereas the d-d subband was overlapped by other structures on its R-branch side. Table II lists the observed wavenumbers, expressed in vat cm-l, for t’he rotational structure of the bands and also gives the standard deviation of the fit to each band or subband. The spectral positions of the measured lines are believed to be determined to within a few t,housandths of a cm-‘, which was also the precision of the near-infrared results. The consistency of the results obtained from different spectral regions is also of the same magnitude as may be seen below, where t>hree independent determinations of the ZJ~band center are compared: ~3 -.___

v3 2439.244 [Ref. (1) ] vA 1928.563 [Ref. (a)]

0 (v4

+

1041.494 [Ref. (.??)I Y.1 530.813 (this work)

vd

(YJ + VS)O-

v.1 r>10.681

Vl

510.681

VEI+ vq vs + V~-

2944.324 [Ref. (1) ] vI 2433.639 [Ref. ( 1) ] VJ 510.685

The values given above for the bands are the observed band centers B’Z” + B”1”’ and the values for vq represent Go(OOO1’Oo) - B( 0001’0”), . III. VIBRATIONAL-TERM

v.

-

VALUES

As

indicated in the Introduction, the knowledge of the vj band center allows the determination of the vibrational term values Go(v) for several levels which had been previously observed as the upper states of “hot” bands originating in the level OOOO”l’. The newly determined term values, listed in Table III, were obtained by combining the band centers, B values and p values from the previous work (1, 2) with the results of the present study and employing t’he following expression for a band center: vB.c. = Go(v’) -

Go(v”)

-

B’Z” + B”t’” f

>s{qvf

-

qgl”‘}.

The uncertainties in the Go(v) values are the sums of the uncertainties of the various components included in the determination. These term values complement the vibrational energy level information recently summarized by Hurlock, Ghersetti, and Rao (4) for “CzDz , “C&HD and “CzHz . IV. VIBRATIONAL

ROTATIONAL

Vibrational rotational interactions resonance effects have been observed

INTERACTIONS

consisting of Z-type doubling and Z-type and discussed previously for levels such as

CzDz BANDS AT 18.6 ,i

P,R OoooO1l

537.781

*

0.001=

331

0.4976 * 0.0016

oooo""o

cn")

9

537.779 i 0.003

3.849

f 0.012

0.120 * 0.011

(0001~1'~0

(f$

OOol'o"

cng)

530.813 1 0.003

3.79

f 0.02

1.39

/ 0.05

0.14 i 0.03

oooo02°

(X,)

0000011

cg)

533.077 i 0.002

3.77

f 0.02

2.36

-i 0.05

0.66 i 0.02

5.38

i 0.08

au)

537.355 0.433

2 0.003

3.60

t 0.15

(0000022)

(0000%2)

(000001~)

c

d

(OOOl"l')~

(a,)

(000001')

@",

(ooolLoO> c

%“cercai”cies represent b

oata frm

c

Table

III

are

d

standard used

in

537.699

(fy

0.016

-2.6

i 0.z

-1.6

f 0.3

deviations. these

calc”latio”s

employing

standard

fomulae.

(0001’11)0 (ZUf or .Z+) of C&D, (f), CzHD (5) and C&H, (6, 7). The effects observed for the level (OOO1lll)o (Z+) consisted of anomalously large rotational distortion and were explained in terms of l-type resonance between the rotational levels of the ;s+ state and the so-called c rotational levels of the A state (000111’)2 (8). The present measurements near 18.6 1 provide direct observations of the Au state for CzDz as well as of the two interacting levels (0000”2”) (Z,+) and (OOOO”2’) (A,). All three of these levels were previously unreported. In the case of the last A state, the observational data provide a means of determining that the c rotational levels of (OOOO”2’) lie above the d levels. The c and d nomenclature for the two components of the l-type doublets follows the convention that for J even, the + level is called c and the - level d. To demonstrate that the c levels are higher, it is sufficient to compare the upper state combination differences A,F’(J) = R(J) - P(J) = F’( J + 1) - F’( J - 1) for the c-c and d-d subbands of the AU-IIU band (0000”2”)-( OOOO”ll)of Table II. Some of the illustrative values are given below in cm-‘: J = 11

A,F:(J)

= 39.250

A$‘/(

J)

= 39.182

J = 14

AzF,‘(J)

= 49.471

AzFd’( J)

= 49.393

J = 16

A,F,I(J)

= 56.290

A,Fd’( J)

= 56.217.

Since the combination differences are larger for the c levels, one infers that the c levels lie above t.he d, since the c and d sequences have the same origin.

5 6 7 8 9 1” 11 12 13 14 15 16 17 18 19 2” 21 22 23 24 25 26 27 28 29 3” 31 32 33 34 35 36 37 38 39 4” 41 42 43 44

2

0 1 2

517.492 515.816 514.143 512.459 51b.776 509.105 507.431 505.764 X4.085 502.406 500.748 499.082 497.408 495.74” 494.083 492.401 490.74” 489.081 487.425 485.773 484.10, 482.46” 480.813 479.146 477.509 475.86” 474.215

524.261 522.558 520.872

534.401. 532.696 531.006 529.317 527.633

L.6s1”-2

541.253 541.479 541.711

538.942 539.076 539.22, 539.377 539.533 539.703 539.86, 540.041 540.223 540.421 540.621

538.123 538.205 538.281 538.373 538.475 538.589

7.4sl”

596.391 598.139 599.881

587.633 589.39, 591.12,

566.416

545.163 546.909 548.683 550.43, 552.202 553.963 555.744 557.52, 559.312 561.081 562.866

539.936 541.663

-3

482.572 480.943 479.32” 477.716 476.092

503.488 501.886 500.304 498.686 497.082 495.4% 493.861 492.245 490.645

531.383 529.69” 528.006 526.335 524.667 X23.008 521.354 519.695 518.063 516.431 514.813 513.174 511.544 509.95” 508.326 506.713 563.806 565.661 567.52, 569.393

558.345 560.162

547.713 549.445 551.215 552.974

544.207

515.919 514.335 512.77, 511.23, 509.688 508.185

520.744 519.096

532.285 530.611 528.934 527.295 525.63” 523.98,

609.435 611.152

605.973

593.925 595.h6” 597.374 599.093 600.818 602.545

588.743 590.476

573.273 575.013 576.72” 578.42, 580.1,” 581.879 583.582 585.30,

569.859

566.416

547.599 549.298 551.01, 552.729 554.439 5%. 152 557.84” 559.552 561.254 562.98,

i.RXlil

592.911 594.658

584. “74 585.851 587.633 519.39,

575.099

571.504

553.519 555.3”” 557.083 558.874 560.682 562.476 564.275 566.075 567.8,”

539.404 541.169

534.242 535.944

-3

41 42 43 44

CzDz BANDS AT 18.6 p

333

TABLE III SOME VIBRATIONAL TERM VALUES OF lZC2Dy

Level

Go(a)(cm-‘)

0000°1’ OOOO”2~ 0000~22 OOO(12)’ 1000°0~ 0010~1’ loo0020 1000~22 0110°1’ 1010°1’

538.629 1070.858 1078.516 1574.829 2705.210 2972.700 3759.377 3767.303 4725.680 5622.422

f f f f f f f f f f

O.OOla 0.003 0.006 0.008 0.004 0.004 0.005 0.007 0.009 0.907

* The uncertainties are sums of the uncertainties of the various components included in the determinations.

The rotational distortion effects observed for interacting levels are also interesting to consider. The band (0000”2”)-(0000”1’) ( z,*-ll,) and the c-c subband of ( 0000°22)-(OOOOo11) (A, - lI,> have the same set of lower levels, namely the c rotational levels of the 11, state (0000”1’). Thus a comparison of the D' - D" values may be considered as a measure of the distortion effects in the upper states. From Table I, these D' - D" values are (2.36 f 0.05) X IO-’ cm-l for the &fll, band and (-2.6 f 0.2) X 1O-6 cm-’ for the A,-& c-c subband. The interacting ACand 2+ levels are seen to exhibit large and nearly opposite distortion effects. It may be noted from Table I that the d-cl subband of the A,--& band does not exhibit a large distortion effect. In the case of the level 000111’, the same type of results are observed and the D' - D" values from the band (OOO1ll’)o-(OOO1’Oo) (Z,+-ll,), (1.39 f 0.05) X low6 cm-‘, and from the c-c subband of (OO01111)2-(OO01100)(A,-&), (-1.6 f 0.3) X 10e6 cm-i, are large and nearly opposite. Because of overlapping discussed above, the d-d subband of the Au--II, band was not completely analyzed and it cannot be directly demonstrated that the c levels of the AUstate (000111’)2 are above the cl levels, but the magnitude and sign of the distortion effect observed for the c levels indicate that they are higher than the d levels. ACKNOWLEDGMENTS Support extended by the National Science Foundation and the Office of Naval Research is gratefully acknowledged. Part of the work done was undertaken under the auspices of the U.S.-Italy Program between The Ohio State University and the University of Bologna. RECEIVED:

November 5, 1971 REFERENCES

1. S. GHERSETTI AND K. NARAHARI RAO, J. Mol. Spectrosc. 28,27 and 373 (1968). 2. S. GHERSETTI,J. PLIVA, AND K. NARAHARI RAO, J. Mol. Spectrosc. 38,.X3 (1971).

334

BALDACCI,

ET AL.

3. J. OVERENDAND H. W. THOMPSON,PTOC.Roy. Sot. (London) A233,291 (1955). 4. S. C. HURLOCK,S. GHERSETTI,ANDK. NARAHARIR.40, Mem. Sot. Roy. Sci. Liege, Collec 87 (1971). 5. A. B~LDACCI,S. GHERSETTI,AND K. NARAHARIRAO, J. Mol. Spectrosc. 34,358 (1970). 6. T. J. COBURN,K. NARAHARIRAO, ENDH. H. NIELSEN, J. Chem. Phys. 26,607 (1956). 7. M. E. MICKELSON,Ph.D. dissertation, The Ohio State University, 1969. 8. G. AMAT AND H. H. NIELSEN, J. Mol. Spectrosc. 2,163 (1958).