Cunha, R D

Kshirsagar, R J

Rajappan, Geeta

IACS Institutional Repository

Indian J. Phys. 76B (4), 525-528 (2002)U P  Ban international journalHigh resolution spectroscopic studies of ntethyl acetylene: analysis of V6band of CDjCfHIR J Kshirsagar*, Geetha Rajappan md R D’CunhaSpectroscopy Division, Modular Laboratories, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, IndiaE-mail : rohidas@magnum.bare.ernci.inAbstract : The high-resolution Fourier transform spectrum of the band of CD3CCH has been recorded at an apodized resolution of U004 cm~' The rotational structure in the T  and fQ  subbands of A = 5 to 9 have been fitted with a standard deviation of 0.0006 cm'* to evaluate the main localized Fermi resonance between the (£) and (V7 + vi vgo) (E) levels. The parameters of both levels and the Fermi interaction parameter have been determined.Keywords : v« band o f CDjCCH, Fermi resonance, vibration-rotation spectra.PACS Nos. : 33.20.Vq, 33.20.Ea, 33.l5.MtI. IntroductionPropyne (CH3CCH) has been found to be abundant in several interstellar molecular clouds [1] as well as in the atmospheres of Titan [2], Jupiter and Saturn [3], Furthermore, optically pumped laser emissions have been observed for this molecule in the far-infrared and midinfrared regions [4,5], For these reasons, its rotational spectrum has been extensively studied in its vibrational ground state as well as excited states [1,3,6]. The vibration-rotation spectra of propyne and its isotopic molecules provide good examples of various kinds of perturbations as all vibrational levels, except perhaps the lowest lying fundamentals, which are expected to be perturbed to some extent by other vibrational levels. The hands of CD3CCH studied so far under high resolution are 2v^ [7], V9 [8 ], V5 and vg [9]. Speirs and Duncan [10] studied Vj band of CD3CCH at medium resolution of 0.2-0.3 enr' and the localized perturbation at ~ 2 2 1 0  cm"' was 'ilentified as a Fermi resonance between the vg* and (vy  ^ + ’'8^  + vio^ ) levels. The resolution that was available to them permitted only a band contour analysis of the Q  subband structure and they were unable to determine the Fermi •oteraction parameter. We have obtained the hi^-resolution^uriespomling AuthorFourier transform spectrum of the V6 band of CD3CCH, and the rotational analysis of the spectral region where the Fermi resonance is prominent is carried out and reported in this paper.2. Experimental detailsThe infrared absorption spectrum of a commercial sample (Merck, Sharpe & Dohme, Canada) of CD3CCH (99% purity) in the spectral region o f2040-2390 cm"' was obtained using a Somem DAS Fourier transform spectrometer. The spectrum was taken with a globar source, KBr beam splitter, and InSb detector at an apodized resolution of 0.004 cm"'. A sample pressure of ~33 Pa (0.25 Torr) was used in a folded cell of fixed path length 10 m. A total of 32 scans were coadded. Wavenumber calibration was performed with suitable water vapor [ 1 1 ] lines in the spectrum.3. Results and discussionThe propyne-d3 (CD3CCH) molecule is a symmetric top with Csv symmetry. It has 10 normal modes of vibration, 5 of species and 5 of species E. The V6 band (antisymmetric CD3 stretching; -2236 cm"'; E  symmetry species) of CD3CCHO 2002 lACS526 R J Kshirsagar, Geetha Rajappan and R D Gunhahas the typical appearance o f  a perpendicular type band o f  a  pro late  sym m etric  top  w ith a large rotational constant /< : the  0  branches are w idely separated and the assignm ent o f  the ro tational quan tum  num ber K  is straightforw ard. The l2-branch assignm ents by Speirs and D uncan [10] w ere largely  confirm ed  in our present studies. An overview  o f  the ve band o f  C D 3C C H , taken at a resolution  o f  0.1 cm  ‘ is show n in F igure 1. A m arked  localized perturbation occurs betw een and at '- 2 2 10 cm ^ T his is ev iden t from  the ^ -b ra n c h  separations w hich dim inish m arkedly  on either side o f  an abn o rm ally  large gap. From  the very  close co rrespondence to  the situation w hich exists in C D 3CN,2205Wavenuitib«r (cm‘')2220' 2235 2250Figure 1. The spectrum of the V6 band of CDjCCII recorded at a resolution of 0.1 cmSpeirs and  D uncan [10] a ttributed  the orig in  o f  this effect to a Ferm i in teraction  o f  the V6 state w ith the com bination  state (v7 -T vg + vio) in C D 3CCH . A sim ilar perturbation  has been observed in the low  resolution  spectrum  o f  the ve band o fTabic 1. Assigned transitions in the vo band of CD3CCIF.1617181920  21 222324252627282930313233C D 3C CD  [12]. The analyses o f  the high resolution spectral o f  the V6 band o f  m ethyl acety lene (C H 3C C H ) or any of ^5 ! isotopom ers have not been reported  so far. In this paper we * report the analysis o f  th is localized Ferm i perturbation m C D 3CCH from our high resolution  data  by fitting the lines in the PP^ and PQk {K  =  5 -9 )  subbands, which arc most affected  by this perturbation . T he assignm ent o f  the J  values in these subbands w ere m ade w ith the aid o f  ground state com bination d ifferences using the constants from Ref |9 j T he upper sta le  energy  levels w ere determ ined by the d iagonalization  o f  a com bined  energy  m atrix of and (v7 + vg -f V|o) levels w ith  off-d iagonal m atrix elements co rresponding  to  Ferm i resonance. T he diagonal matrix elem ents are given by the standard  polynom ial expression.E , j  =G, + + l)+(A, - B,)K^ - D;!J-(J+l]'y D f j ( J  + \ ) K ^ ~ D l^ K *  ~ [ 2 ( A C ) y k . l ]w here /k =  |A | and the splitting  o f  the ± I  components through 2-axis C orio lis coupling, given by the term  in square bracket, is relevant only  for degenerate  stales. The ofl* d iagonal m atrix  elem ent for Ferm i resonance is given by,^ ( v ^ ', / c |w l ( v 7 + V j+ v ,o ) '^ ',A '^  = j rT he assigned  tran sitions are listed  in T able  1, and tlie param eters derived from  the least-squares fit are given in Table 2. 'I'he blended lines (w ith hot hand transitions, or o ther lines) w ere excluded from  the fit. T he param eters ol the (V7 + v« -b V|o) (£ )  state, to  w hich transitions are not observeObs Q-C Obs 0 -C Obs 0 c"Pi 34 2199.4993 23- 16 2198.95139708 <991 7 c ♦ 35 2198.9927 8 17 2198.4484Z j36 2198.4861 -3 18 2197 9437 02208.038 22* t ^2207.5352 -13* PPt19202197 4371 2196 9343-13172207.038 11 n2206.5389 2 1 ’ 13 2206.522 121 2196 4258 U2206.0361 -1 14 2206 0192 13*2205.5352 -1 15 2205 5182 -3 PPt2205.0342 0 16 2205.0154 -5 7 2199.8854 -282204.5333 8 17 2204 5125 0 8 2199.3919 -262204.0304 0 18 2204 0078 -8 9 2198.9004 -12203.5295 15* 19 2203 5031 -9 10 2198.4089 282203.0248 -4 20 2202 9984 -4 11 2197.9173 6 1 '2202.5219 -2 21 2202 4937 6 12 2197.4126 3^1'2202.0191 4 22 2201 9908 40* 13 2196.9079 -121'2201.5144 -5PPi14 2196.4145 -95'2201.0115 6 15 2195.9211 A A ^2200.5068 2 14 2199.955 -9 16 2195.4277 -292200.0021 i 15 2199.4522 18* 17 2194.9342 1High resolution spectroscopic studies o f methyl acetylene etc 52TTable I. (Cont'd.lJ Obs1819:o2122232425 2^2728 29 U) 5 i3233242526272829303132333435361920 21 22 232194.43332193.93612193.43892192.93992192.44272191.94362191.4372190.9436 2190.4464 2189.9417 2189.4407 2188.93792188.437 2187.9341 2187.4294 2186.92472187.46712186.972186.47272185.97372185 47652184.97742184.47832183-97932183.4802 2182,9793 2182 4783 2181 97922181.48022216.8461 2216 8366 2216.8253 2216.814 2216.80270-C-2 4 ’-16-5- 81013-54*1 2 *44*56 -70- 8-32*-53*-15*-70-574246-7^2 1 *-14*-5590-5- 6242526272829303132333435361314151617181920 21 2223241617181920  21 22 23Obs2216.7914 2216 7801 2216.767 2216.7538 2216.7406 2216 7274 2216.7123 2216 6992 2216 6841 2216 669 2216.654 2216 6389 2216 622•V .2213.3884 2213.3771 2213 3639 2213.3526 2213 3394 2213.3244 2213 3112 2213.2961 2213 281 2213 2679 2213 249 2213 2358^Vi2207.2866 2207 2734 2207.2583 2207 2433 2207 2282 2207.2113 2207 1943 2207 1755O-C-34-I-5-40-1 11- 2- 217-163- I I *00- 1 2 *00537*17*60*02- 6- 62187202122232425262728293031323334353637383940232425262728293031323334Obs2203.73662203.72352203.7142203.70652203.69712203.68582203.67642203 66322203.65192203.64062203.62552203.61232203.59732203.5973 2203.5822 2203.5671 2203.54832203.52952203.5295 2203 5031 2203.4824PQ<,2199.72532199.71772199 71022199.70082199.69332199.68382199.67442199.6652199.65562199.64622199.6332199 6217C)-C38*-4- 6  14* 2 0 * 1 1 24* 4 6II*-16*2 2 *-43*89*74*63*18*- 2 2 *126*15*-35*-9- 61-66213714*-14- 2 2 *‘^ Ihc ob.servcd values arc in cm“* and the residuals (O-C) are in cm"’ x 10  ^ Lines marked with asterisks were excluded from the fit. iable 2. Molecular parameters for ve and (vy  ^ vjj + vio) stales of CD^ CCH" _______Ciround .*>1310 V6 State V7 vi + Vjo StateG 0.0* 2235 05887 (178) ^ 2192.67747 (195)B 0.24536128* 0.24509854 (256) 0.2439MS (130)2 4H6* 2.398583 (142) 2.376696 (394)/>'x 10’ 0.7237* 0.6088 (131) 0.7237*10-^ 0.341774* 0 27867 (206) 0.341774*/y  X 10^ 0.225* 0 20491 (871) 0.225*{U (» ) 0.846464 (965) 8.70093 (191)0216537 (372)^0. of lines assigned 150No* of lines used 98RMSD (cm"') X 10^ 5.7"All values are in cm-'. The standard deviation of the parameters given in parantheses arc in i Constrained parameter. ‘'From Ref. (9J.528 R J  Kshirsagar, Geetha Rajappan and R D ’Cunhain the spectrum, are not completely determinable. The values for the fundamentals given by Speirs and Ducan [10] were used and for the combination band *^(V7 + vg + vjo) = “ C? + Cs + ^10- In the least-squares analysis, the starting values for (2A ) used were 0.8343 cm" ‘ and 8.7 cm ' for the V6 (£) and (v; + vg + vio) (£) states, respectively, which are very close to the values obtained from the fit as seen from Table 2.4. ConclusionThis study explains the major localized Fermi resonance between the V6 and (v7 + vg + vio) band of CD3CCH. About 150 lines in the ’’Pk {K  = 5-7) subh^ds could be fitted to a standard deviation of0.0006 cm~', which is comparable to the precision of the measurements. The molecular parameters for tile Vg and (v7 + vg + V|o) combination states and the Fermi interaction parameter have been obtained with statistical significance. Efforts are being made to asign the lines of all the subbands, with the inclusion of additional perturbations in the least-squares fit for complete analysis of this band and the results will be reported soon.AcknowledgmentWe thank Dr. T K Balasubramanian, Head, Spectroscopy Division, BARC for his kind encouragement and interest in the work.R e fe rrn c c i[ 1 ] G Wlodarczak, R Bocquet, A Bauer and J Demaison j  Moi Specirosc. 129 371 (1988)[2] W C Maguire, R A Hanel, D E Jennings, V G Kunde an. R E Samuelson Nature (London) 292 683 (1981)[3] G Graner and G W agner J. Molec. Spectrosc  144 ]g(1990)[4] E Arim ondo, M C iocca and G B aldacchini Revie^ii  ^In fla te d  and M illim eter W aves eds. K J Button, M Inguwi and. F Strumia (New York : Plenum) Vol. 2 (1984)[5] T At Adlouni and G Graner J. Molec. Spectrosc. 127 U (1988)[6 ] W M Rhce and J A Roberts J. Molec. Spectrosc. 126 35 (1987)[7] K Singh, G Rajappan, V A Job, V B Kartha, A Weber an W B Olson J. Molec. Spectrosc. 157 467 (1993)[8 ] N S Sule, R J Kshirsagar and V A Job J. Molec. S p e c im  160 502 (1993)[9] G eetha Rajappan and V A Job Can. J. Chem 71 168(1993)[10] G K Speirs and J L Duncan J. Molec. Spectrosc 51 27 (1974)[11] G Guelachvili and K Narahari Rao Handbook o f  Infrare Standards (New York : Academic Press) (1986)112] R Anttila, M Lauronen and L Kaarela Repa-t No. 68, Deparimi o f Physics, Um. o f  Oulu, Finland (1979)

High Resolution Spectroscopic Studies of Methyl Acetylene: Analysis of v6 Band of CD3CCH

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High Resolution Spectroscopic Studies of Methyl Acetylene: Analysis of v6 Band of CD3CCH

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