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The ground state infrared spectrum of the MnH radical (7Σ) from diode laser spectroscopy
Volume 163, number I
CHEMICAL PHYSICS LETTERS
3 November 1989
THE GROUND STATE INFRARED SPECTRUM OF THE MnH RADICAL (‘Z) FROM DIODE LASER SPECTROSCOPY Rolf-Dieter URBAN and Harold JONES Abteiiung Physikalische Chemie, Universitiit Urn, D-7900 Urn, Federal Republic ojGermany
Received 17 July 1989; in final form 5 August 1989
The infrared spectrum of the manganese hydride radical (5JMnH) in its ground electronic state (‘2) has been observed using a diode laser spectrometer. The wavenumbers of twelve transitions of the v= 14 band, five of the v= 2 t 1 band and seven of the v=&-2 band have been measured with a nominal accuracy of +O.OOl cm-‘. Coupling between the electronic spin (S=3) and the overall molecular rotation causes each ro-vibrational transition with N> 3 to be split ( y splitting) into seven components each separated by a few hundredths of a wavenumber. In most cases the complete structure was resolved. Correction terms arising from spin-spin coupling had to be included in the analysis. This work has produced the most accurate set of ground-state parameters available for MnH.
1. Introduction The unusual electronic configuration of maganese monohydride with its six unpaired electrons has caused it to be the object of considerable interest for spectroscopists for many years. The first investigations of the electronic spectrum of MnH were carried out by Heimer [ 1] and Gaydon and Pearse [ 21. Extensive work was subsequently carried out on the A 711-X ‘C band system observed in emission from discharge-excited MnH and MnD by Nevin and coworkers [ 3-8 1. A 2 1 ft, grating spectrometer was used in the later measurements and a number of molecular parameters were determined quite accurately. In the present paper we report the observation of the infrared spectrum of 55MnH (manganese has only one isotope) in its ground electronic state. These measurements have a much higher resolution than that achieved in the classical electronic spectra. Also, unlike the measurements on the electronic spectra, information on the ground state hyperfine splittings was obtained directly without having to contend with the complications of the A ‘II state. There have been a number of publications from this laboratory in recent years using tunable diode laser spectroscopy to obtain accurate infrared spectra of a number of metal hydrides in the gas phase. 34
TheseincludeNaH [9],CsH [lO],BaH [ll],SrH 1121, RbH [ 131, GaH [ 141, InH [ 151, TlH [ 161, CdH and ZnH [ 17 ] and most recently AgH [ 18 1. Similar measurements have been carried out in other laboratories on KH [ 191, on MgH and CaH [ 201, and on LiH [ 211 and there have been several recent reports of the use of CO-laser LMR spectroscopy to observe the spectra of diatomic hydride radicals (e.g. SnH, NiH, FeH, CoH [22] and GeH 1231).
2. Theory In his analysis of the spectra of the A ‘H-X ‘C band of MnH, Nevin [4] assumed that the ground state could be described by a Hund case (b) coupling scheme [24]; however, transitions with high values of the rotational quantum number did not appear to be adequately reproduced. Pacher [ 25 ] and Kovacs and Pacher [ 261 later reanalysed Nevin’s data. These authors included the effects of perturbations between the A ‘Il and X ‘2 states and carried out a simultaneous fit of the parameters of these two states. We have found, however, that our accurate infrared ground state data can be very adequately fit
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by application of slightly modified versions of the Hund case (b) expressions given by Nevin [ 41 and tabulated by Kovacs [27 1. In the X ‘2 ground state of MnH the case (b) scheme is simply S+N=J where S is the spin angular momentum, N the rotational angular momentum and J the total angular momentum. Since S=3 in MnH, the J quantum numbers run from NS 3 to N- 3. Under these circumstances the energy of the ground state levels is the sum of contributions from these sources: E=&R+EsR+&s,
(1)
where EVR is the normal ro-vibrational energy, ESR is the contribution from the spinyrotation interaction and Ess comes from the spin-spin interaction. EVR is given by the usual Duham [ 281 energy expression for a molecule in a ‘Z state EvR= c Y,(v+f)‘[iV(N+l)]J. rj
(2)
&R can be expressed in a form similar to that used extensively for 2C molecules, e.g. [ 11,12,17 ] &R=_&R
1
%j
[N(N+l)l',
(3)
‘I
where the yii are spin-rotation coupling parameters with varying vibrational and rotational dependence and fsR has been tabulated by Nevin [ 41. The energy contribution from spin-spin coupling has again been tabulated by Nevin [4] and we introduce a vibrational and rotational dependence in a manner analogous to that used above Ess=&
c ~u(v+~)’ [N(N+l)]‘,
ij
(4)
where eij is the spin-spin interaction parameter and the values of fss are given in ref. [ 41. The effects of spin-spin interaction are relatively small and if these are at first neglected, the combination of eqs. (2) and (3) predicts that each transition should display a pattern of seven uniformly spaced lines. The frequency of the central line of this pattern is given by eq. (2). If the vibrational dependence of the spinrotation parameter, y, is neglected, the individual components are separated by approximately yO,.
3 November 1989
The inclusion of spin-spin interaction (eq. (4) ) introduces terms which disturb the symmetry of the pattern and which also produce a slight N-dependence in the frequency of the central line. A computer program was written which allowed the individual line frequencies to be fitted directly to eq. (1).
3. Experimental The apparatus used in this work was the same as used previously for the observation of the infrared spectra of a number of diatomic hydrides [ 9-18 1. The sample of MnH was produced by heating several grams of manganese metal to about 1100°C in an aluminium oxide ceramic tube ( 150 cm long, 20 mm inner diameter) and reacting the metal vapor with hydrogen (8 mbar) in an electric discharge ( 300 mA at 6 kV). The hydrogen was slowly flowed through the cell to avoid the build-up of impurities. Measurements were carried out for several days using a single charge of manganese. Strong absorption lines of MnH were observed with a single pass of the laser beam through an effective absorption pathlength of approximately 80 cm. The diode laser spectrometer used was based on the laser head assembly of Spectra Physics with diodes from the same company. Measurements were carried out to a nominal accuracy of 0.00 1 cm-’ using a calibrated confocal etalon with a FSR of 0.009811 cm-’ in conjunction with accurately measured absorption lines. The spectral range searched extended from 1200 to 1560 cm-‘. Absolute wavenumber calibration was carried out using accurately known absorption lines of SO1 [ 29 1, NzO [ 301 and formaldehyde [ 3 11. The diode laser beam was passed axially through the cell onto a HgCdTe infrared detector. Signals were processed by source modulation of the diode laser at 8 kHz followed by phase sensitive detection.
4. Spectra and analysis Two examples of the septet pattern displayed by all the lines of MnH are given in figs. 1 and 2. These figures show respectively the P( 7) and R( 5) tran35
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1405.70
CHEMICAL PHYSICS LETTERS
1550&l .M)
1405.90
1550.90
cm-’
cm-f
Fig, 1. The P( 7) transition of the fundamental band of MnH in its ground electronic state. The septet structure arises from the couplingof the spin of the six unpaired electrons (S=3) with the overall motion. The relevant values of S are indicated above each component. In the P-branch transitions the most intense component, with &IV+ 3, is positioned at the low frequency end of the pattern. The upper trace shows the interference fringes from the calibration Won, which has a FSR of 0.0098 cm-‘. The individual components are separated by approximately 0.035 cm-’ in this case. Time constant 30 ms.
sitions of the fundamental band. As can be seen, in the P-branch transitions (fig. 1) the strongest line, which corresponds to J=N+ 3, is at the low frequency end of the pattern, whereas in the R-branch (fig. 2) the intensity pattern is reversed. At first sight, the patterns shown in figs. 1 and 2 appear to display a regular frequency spacing, as would be expected as a result of the presence of only spin-rotation coupling. However, closer inspection reveals that the separations between the seven individual spin-rotation components are not exactly the same. Slight variations are present as a result of the spin-spin coupling. The data obtained are shown with their assignments in table 1. As can be seen from these data the observed hyperfine pattern was less widely spaced in the R-branch than in the P-branch and this effect increased with increasing vibrational excitement. As a result, the R ( 18) transition of the v=3t2 band was 36
3 November 1989
Fig. 2. The R( 5 ) transition of the fun&mental band near I55 1 cm-‘. The most intense component it at the high frequency end of the septet battern in the R-branch transitions. In this case the components are separated by approximately 0.02 cm-‘. Time constant 30 ms.
observed as a single broad line. The predicted spinrotation splitting between the individual components was only of the order of 1F3 cm-’ in this case. The data of table 1 were fitted to eq. ( 1) and the residuals are shown in parentheses in table 1. The parameters fitted and the values obtained are shown in the first column of table 2. The results obtained by Nevin [4] for some of these parameters are included for comparison.
5. Discussion As can be seen from table 2, the present work has greatly improved the accuracy of the ground state parameters of MnH and almost all of the higher-order parameters have been determined for the first time. This is particularly true of the vibrational parameters for which only approximate values were previously available. Nevin’s data [ 41 on the A 711+X ‘2 emission band of MnH was reanalysed at a much later data by Pacher [ 25 ] and again by Kovacs and Pacher [ 26 1. However, we have chosen to list mainly Nevin’s
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original data from 1945 in table 2 since these are generally in better agreement with the present work and there seem to be some inconsistencies in the resuit of ref. [ 261.
3 November I989
As can be seen from table 2, Nevin’s values [ 41 for the rotational parameters B, ( Yo,), D, ( Yaz), and (Y, (Y,,) are in admirable agreement with the results from our accurate measurements. This may, how-
Table 1 Observed transitions of manganese hydride. Number in parentheses represent obs. -talc. in units of the last digit Transition (cm- ’) rklc0
Transition (cm-i)
0 1 2 3
1405.9167( - 18) 1405.8841(-00) 1405.8475( -07) 1405.8107(-03) 1405.7729( -03) 1405.7353 (-02) 140X6994( 07)
P( 6) P( 6)
S= S=
8) 8) 8) 8) 8) 8) 8)
s=-3 s= -2 IS=-1 s= 0 s= 1 s2 s= 3
1392.6532(-14) 1392.6184(-10) 1392.5816(-12) 1392.5457( 04) 1392.5072( 00) 1392.4701( 09) 1392.4321( 04)
P( P( P( P( P( P( P(
5) 5) 5) 5) 5) 5) 5)
S=-3 s=-2 SE--l s= s= s= s-
9) 9) 9) 9) 9) 9) 9)
s=-3 s--2 Is=-1 s= s= s= SF
0 1 2 3
1379.1244(-17) 1379.0903( 01) 1379.0524( -08) 1379.0148( -04) 1378.9768( 00) 1378.9390( 06) 1378.9013( 09)
P( P( P( P( P( P(
4) 4) 4) 4) 4) 4)
P(l0) P(l0) P(l0) P(10) P(l0) P(l0) P(l0)
s--3 s=-2 s=-1 s= s= s= s=
0 1 2 3
1365.3414( 11) 1365.3037(-01) 1365.2681( 19) 1365.2277( -02) 1365.1904( 12) 1365.1512( 08) 1365.1130( 11)
P(l1) P(l1) P(ll) P(l1) P(l1) P(l1) P(l1)
s=-3 s=-2 s=-1 s= s= s= s=
P(l7) P(17) P(17) P(17) P(17) P(17) P(17)
s=-3 s=-2 s=-1 s= s= s= s=
P( P( P( P( P( P( P(
7) 7) 7) 7) 7) 7) 7)
s=-3 s=-2 SC-1 s= s= As= .s=
P( P( P( P( P( P( P( P( P( P( P( P( P( P(
2 3
1418.7303( 1418.6955(
0 2 3
1431.6244( 04) 1431.5931( 10) 1431.5581( 07) 1431.5221( 14) 1431.4831( 02) 1431.4450(-05) 1431.4098( -05)
s=-2 s=-1 s= ss= s-
0 1 2 3
1444.0233( 13) 1443.9895( 12) 1443.9517( 04) 1443.9126( 01) 1443.&X720( 25) 1443.8375( -28)
P( 3) P( 3)
s= s=
2 3
1456.0095( 02) 1455.9754(-11)
0 1 2 3
1351.3027(-15) 1351.2656(-16) 1351.2284(-08) 1351.1907( 02) 1351.1514(-01) 1351.1130( 07) 1351.0738( 03)
P( 2) P( 2) P( 2)
s= s= s=
1 2 3
1467.9094(-19) 1467.8456( 39) 1467.8086( -25)
0 1 2 3
1262.2289( 19) 1262.1874(-05) 1262.1483( 00) 1262.1085( 03) 1262.0679( 00) 1262.0271(-03) 1262.9857(-13)
R( R( R( R( R( R( R(
S=-3 S=-2 S=-I S= S= S= S==
0
1550.7949( -07) 1550.8195(- 18) 1550.8469( -03) 1550.8740( 09) 1550.9005( 18) 1550.9242( 08) 1550.9478( 13)
5) 5) 5) 5) 5) 5) 5)
1
I 2 3
03) 15)
37
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3 November 1989
Table 1 (continued) Transition (cm- ’)
Transition (cm-‘) v=2t-1
~~3-2
7) 7) 7) 7) 7) 7) 7)
s=-3 S=-2 s=-1 s= s= s= s=
P(l4) P( 14) P(l4) P(l4) P(l4) P(l4) P(l4)
SE-3 s=-2 s=-1 Is= s= s= s=
P(l5) P(15) P(l5) P(l5) Ul5) P(l5) P(l5)
s=-3 s=-2 s=-1 s= s= s= s=
Pt P( Pt w Pt P( Pt
8) 8) 8) 8) 8) 8) 8)
s=-3 s=-2 s=-1 s= s= Is= s=
WlO) P(lO) P(lO) P(lO) P(lO) WlO) P(lO)
s=-3 s=-2 s=-1 s= s= s= s=
P(ll) P(ll) Wll) P(ll) Wll) P(ll) P(ll)
s=-3 s=-2 s=-1 s= s= s= s=
P( P( P( w P( P( P(
0 1 2 3
1350.0734( -01) 1350.0408( 10) 1350.0047( 03) 1349.9681( 05) 1349.9305( 03) 1349.8942( 14) 1349.8570( 07)
2) 2)
s=-1 s= 0 s= 1 s= 2
1463.2900( 07) 1463.3176(-32) 1463.3533( - 16) 1463.3892( 19)
0 1 2 3
1253.7035( 09) 1253.6629( - 16) 1253.6255( 00) 1253.5861( 01) 1253.5450( - 11) 1253.5054( -06) 1253.4648( - 11)
R(ll) R(11) Wll) Rtll) R(11) Rtll) Nil)
s=-3 s=-2 s=-1 h-0 s= 1 s= 2 s= 3
1535.5121( 08) 1535.5289( 05) 1535.5447( -02) 1535.5598( - 10) 1535.5747( - 12) 1535.5898( -04) 1535.6031(-05)
0 1 2 3
1238.9525( 08) 1238.9138( 07) 1238.8749( 10) 1238.8351( 10) 1238.7941( 02) 1238.7534( -01) 1238.7118(-14)
R(14) R( 14) R(14) R( 14) R( 14) R(.l4) R(14)
s=-3 s=-2 ..%-I s= 0 s= 1 s= 2 s= 3
1552.3491( 18) 1552.3607( 08) 1552.3719( 01) 1552.3819(-09) 1552.3922( -09) 1552.4025 ( 00) 1552.4117( 06)
0 1 2 3
1279.6148( -04) 1279.5817( 04) 1279.5461( 03) 1279.5089( -02) 1279.4711(-06) 1279.4342( 00) 1279.3979( 05)
P( P( P( P( P( P(
7) 7) 7) 7) 7) 7)
s=-2 s=-1 s= s= s= s=
0 1 2 3
1292.3069( -02) 1292.2717( -06) 1292.2358( -03) 1292.1986( -05) 1292.1620( -01) 1292.1273( 13)
0 1 2 3
1253.3219( -14) 1253.2863( - 14) 1253.2494( - 16) 1253.2121(- 12) 1253.1757( 07) 1253.1356( -09) l253.0974( -09)
R R R R R R
(4) (4) (4) (4) (4) (4)
s=-2 s=-1 s= 0 s= 1 s= 2 s= 3
1420.3590( -03) 1420.3850( 11) 1420.4086( -03) 1420.4334( -04) 1420.4587( 13) 1420.4808( 22)
0 1 2 3
1239.7694( 1239.7330( 1239.6954( 1239.6576( 1239.6193( 1239X03( 1239.5417(
R( R( R( Rt R( R( R(
5) 5) 5) 5) 5) 5) 5)
s=-3 s=-2 s=-I s= s= s= s=
0 1 2 3
1428.7556( 04) 1428.7782( -01) 1428.8009( -08) 1428.8234( - 16) 1428.8475 ( -04) 1428.8693( -04) 1428.8901( 04)
s=
0
1500.3247( -02)
08) 07) 04) 08) 12) 11) 13)
R( R( R( Rt
2) 2)
R(18)
ever, be a little pilation, Huber rected values agreement with 38
fortuitous, since in their data comand Herzberg [ 321 published corwhich are in slightly less good our values.
The present work seems to show no evidence that the ground state of MnH displays any unusual effects arising from the perturbations discussed by Kovacs and Pacher [ 261. This may be due to the fact that
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CHEMICAL PHYSICS LETTERS
Table 2 Parameters determined for manganese hydride (cm-‘). Numbers in parentheses represent one standard deviation in units of the last digit This work
Y10 Y20
Nevin [4]
Y,,XlO Y,,X 105 Yj,X104 Y0,X lo4 Yl2X 106 Yz*x 106 Y03x lo9 YOlx 102 YIIx 104 hlX 10S Yozx 106 co*x 103 &X lo4
1546X536(15) -27.60280(91) -3.0822(15) 5.685795(37) - 1.60488(22) 4.05(91) -3.255(13) -3.0630(30) 2.983(68) -1.201(16) 8.68(60) 3.2055(83) -8.32( 13) -3.40(33) -7.54(21) -2.234(82) -1.30(18)
‘) Ref. [S].
“Ref. [25].
Y,,x 10
yo,
64
&&
1548.0 a> 28.8 a)
& ol,XlO
5.68548 1.6079
0,x
10’ B,x lo6
3.03 15 1.46
Hex lo9 Yc
9.10
yD,x lo6 cxlO3
3.13
-6.;(4) -4.0
3 November 1989
patterns extend over only 0.2 cm-’ at most, the peak height of the signals observed should have a fair correlation with the intensity variation of the individual components within a transition. The intensity pattern of the P( 7) transition shown in fig. 1 is in reasonable agreement with the expected pattern, whereas the R( 7) (fig. 2) agree far less well. The main feature expected of the relative intensities is that they should increase with increasing magnitude of J. This was generally observed, but the expected detailed behaviour did not always appear to be present. Further discussion of this problem will require better relative intensity measurements than are available at the moment.
Acknowledgement b,
our data does not include transitions with such high values of the rotational quantum number as those measured by Nevin [4], but all that can be said at present is that the ground state of MnH appears to be quite “normal”. With the exception that two spinspin parameters (eol and a rotational correction term ~~~~were introduced, the fitting of the data of table 1 required no more variables than were used in our analysis of the spectra of several ‘C molecules [ 11,12,16,17] _Indeed, in the cases of ZnH and CdH [ 171, due to the presence of strong anharmonicity, more parameters were required than were used here for MnH (e.g. five y parameters compared to the four used here) _ Relative intensities. The relative intensities of the individual hyperfme components would be expected to be similar to that observed in comparable situations with the coupling of nuclear spin to overall molecular rotation and S-L coupling in an atom. For these cases, the relative intensities have been tabulated in numerous textbooks (e.g. ref. [ 33 1). Intensities cannot be determined very accurately from diode laser spectra since the output power of the diode varies across the mode. However, since the
This work is supported by the Deutsche Forschungsgemeinschaft. The authors wish to thank U1rich Magg for his aid with the programming and for helpful discussions.
References [ I] T. Heimer, Naturwissenschaften 24 ( 1936) 52 1. [ 21 A.G. Gaydon and R.W.B. Pearse, Nature 139 ( 1937) 590. [ 31 T.E. Nevin, Proc. Roy Irish Acad. 48 (1942) 1. [4] T.E. Nevin, Proc. Roy Irish Acad. 50 (1945) 123. [5]T.E.NevinandP.G.Doyle,Proc.RoyIrishAcad.52(1948) 123. [ 61 T.E. Nevin, M. Conway and M. Cranley, Proc. Phys. Sot. (London)A62(1952) 115. [ 71 T.E. Nevin and D.V. Stephens, Proc. Roy Irish Acad. 55 (1953) 109. [S] W. Hayes, P.D. McCarvill and T.E. Nevin, Proc. Phys. Sot. (London) 70 (1957) 904. [9] U. Magg and H. Jones, Chem. Phys. Letters 146 ( 1988) 415. [ 101 U. Magg and H. Jones, Chem. Phys. Letters 148 ( 1988) 6. [ 111U. Magg, H. Birk and H. Jones, Chem. Phys. Letters 149 (1988) 321. [ 121U. Magg, H. Birk and H. Jones, Chem. Phys. Letters 15 1 (1988) 263. [ 131U. Magg. H. Birk and H. Jones, Chem. Phys. Letters 15 1 (1988) 503. [ 141 R.-D. Urban, U. Magg and H. Jones, Chem. Phys. Letters 154 (1989) 135. [ 151A.H. Bahnmaier, R.-D. Urban and H. Jones, Chem. Phys. Letters 155 (1989) 269.
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[ 161 R.-D. Urban, A.H. Bahnmaier, U. Magg and H. Jones, Chem. Phys. Letters 158 (1989) 443. [ I 7 ] R.-D. Urban, U. Magg. H. Biik and H. Jones, J. Chem. Phys., to be published. [ 181 H. Birk and H. Jones, Chem. Phys. Letters 161 (1989) 27. [ 191 N.N. Haese, D.J. Liu and R.S. Altman, J. Chem. Phys. 81 (1984) 3766. [20] B. Lemoine, C. Demuynck, J.L. Destombes and P.B. Davies, J. Chem. Phys. 89 (1988) 673. [ 211 C. Yamada and E. Hirota, J. Chem. Phys. 88 ( 1988) 6702. [ 221 W. Urban et al., Spring Conference of the German Physical Society, Essen (March 1989). [23] J.M. Brown, private communication. [24] F. Hund, Z. Physik 43 ( 1927) 805.
40
3 November 1989
(251 P. Pacher, Acta Phys. Acad. Sci. Hung. 35 (1974) 73. [26] I. Kovacs and P. Pacher, J. Phys. B 8 (1975) 796. [ 271 I. Kovacs, Rotational structure in the spectra of diatomic molecules (Hilger, London, 1969). [ 281 J.L. Dunham, Phys. Rev. 41 ( 1932) 72 1. [ 291 G. Guelachvili, O.N. Ulenikov and G.A. Yshakova, J. Mol. Spectry.108 (1984) 1. [30 ] G. Guelachvili and K.N. Rao, Handbook of infrared standards (Academic Press, New York, 1986). [ 3 I] S. Nadler, D.C. Reuter, SJ. Daunt and J.W.C. Johns, NASA technical memorandum 100709 (1988). [32] K.P. Huber and G. He&erg, Constants of diatomic molecules (Van Nostrand Reinhold, New York, 1979). [ 331 C.H. Townes and A.L. Schawlow, Microwave spectroscopy (McGraw-Hill, New York, 1955).
CHEMICAL PHYSICS LETTERS
3 November 1989
THE GROUND STATE INFRARED SPECTRUM OF THE MnH RADICAL (‘Z) FROM DIODE LASER SPECTROSCOPY Rolf-Dieter URBAN and Harold JONES Abteiiung Physikalische Chemie, Universitiit Urn, D-7900 Urn, Federal Republic ojGermany
Received 17 July 1989; in final form 5 August 1989
The infrared spectrum of the manganese hydride radical (5JMnH) in its ground electronic state (‘2) has been observed using a diode laser spectrometer. The wavenumbers of twelve transitions of the v= 14 band, five of the v= 2 t 1 band and seven of the v=&-2 band have been measured with a nominal accuracy of +O.OOl cm-‘. Coupling between the electronic spin (S=3) and the overall molecular rotation causes each ro-vibrational transition with N> 3 to be split ( y splitting) into seven components each separated by a few hundredths of a wavenumber. In most cases the complete structure was resolved. Correction terms arising from spin-spin coupling had to be included in the analysis. This work has produced the most accurate set of ground-state parameters available for MnH.
1. Introduction The unusual electronic configuration of maganese monohydride with its six unpaired electrons has caused it to be the object of considerable interest for spectroscopists for many years. The first investigations of the electronic spectrum of MnH were carried out by Heimer [ 1] and Gaydon and Pearse [ 21. Extensive work was subsequently carried out on the A 711-X ‘C band system observed in emission from discharge-excited MnH and MnD by Nevin and coworkers [ 3-8 1. A 2 1 ft, grating spectrometer was used in the later measurements and a number of molecular parameters were determined quite accurately. In the present paper we report the observation of the infrared spectrum of 55MnH (manganese has only one isotope) in its ground electronic state. These measurements have a much higher resolution than that achieved in the classical electronic spectra. Also, unlike the measurements on the electronic spectra, information on the ground state hyperfine splittings was obtained directly without having to contend with the complications of the A ‘II state. There have been a number of publications from this laboratory in recent years using tunable diode laser spectroscopy to obtain accurate infrared spectra of a number of metal hydrides in the gas phase. 34
TheseincludeNaH [9],CsH [lO],BaH [ll],SrH 1121, RbH [ 131, GaH [ 141, InH [ 151, TlH [ 161, CdH and ZnH [ 17 ] and most recently AgH [ 18 1. Similar measurements have been carried out in other laboratories on KH [ 191, on MgH and CaH [ 201, and on LiH [ 211 and there have been several recent reports of the use of CO-laser LMR spectroscopy to observe the spectra of diatomic hydride radicals (e.g. SnH, NiH, FeH, CoH [22] and GeH 1231).
2. Theory In his analysis of the spectra of the A ‘H-X ‘C band of MnH, Nevin [4] assumed that the ground state could be described by a Hund case (b) coupling scheme [24]; however, transitions with high values of the rotational quantum number did not appear to be adequately reproduced. Pacher [ 25 ] and Kovacs and Pacher [ 261 later reanalysed Nevin’s data. These authors included the effects of perturbations between the A ‘Il and X ‘2 states and carried out a simultaneous fit of the parameters of these two states. We have found, however, that our accurate infrared ground state data can be very adequately fit
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by application of slightly modified versions of the Hund case (b) expressions given by Nevin [ 41 and tabulated by Kovacs [27 1. In the X ‘2 ground state of MnH the case (b) scheme is simply S+N=J where S is the spin angular momentum, N the rotational angular momentum and J the total angular momentum. Since S=3 in MnH, the J quantum numbers run from NS 3 to N- 3. Under these circumstances the energy of the ground state levels is the sum of contributions from these sources: E=&R+EsR+&s,
(1)
where EVR is the normal ro-vibrational energy, ESR is the contribution from the spinyrotation interaction and Ess comes from the spin-spin interaction. EVR is given by the usual Duham [ 281 energy expression for a molecule in a ‘Z state EvR= c Y,(v+f)‘[iV(N+l)]J. rj
(2)
&R can be expressed in a form similar to that used extensively for 2C molecules, e.g. [ 11,12,17 ] &R=_&R
1
%j
[N(N+l)l',
(3)
‘I
where the yii are spin-rotation coupling parameters with varying vibrational and rotational dependence and fsR has been tabulated by Nevin [ 41. The energy contribution from spin-spin coupling has again been tabulated by Nevin [4] and we introduce a vibrational and rotational dependence in a manner analogous to that used above Ess=&
c ~u(v+~)’ [N(N+l)]‘,
ij
(4)
where eij is the spin-spin interaction parameter and the values of fss are given in ref. [ 41. The effects of spin-spin interaction are relatively small and if these are at first neglected, the combination of eqs. (2) and (3) predicts that each transition should display a pattern of seven uniformly spaced lines. The frequency of the central line of this pattern is given by eq. (2). If the vibrational dependence of the spinrotation parameter, y, is neglected, the individual components are separated by approximately yO,.
3 November 1989
The inclusion of spin-spin interaction (eq. (4) ) introduces terms which disturb the symmetry of the pattern and which also produce a slight N-dependence in the frequency of the central line. A computer program was written which allowed the individual line frequencies to be fitted directly to eq. (1).
3. Experimental The apparatus used in this work was the same as used previously for the observation of the infrared spectra of a number of diatomic hydrides [ 9-18 1. The sample of MnH was produced by heating several grams of manganese metal to about 1100°C in an aluminium oxide ceramic tube ( 150 cm long, 20 mm inner diameter) and reacting the metal vapor with hydrogen (8 mbar) in an electric discharge ( 300 mA at 6 kV). The hydrogen was slowly flowed through the cell to avoid the build-up of impurities. Measurements were carried out for several days using a single charge of manganese. Strong absorption lines of MnH were observed with a single pass of the laser beam through an effective absorption pathlength of approximately 80 cm. The diode laser spectrometer used was based on the laser head assembly of Spectra Physics with diodes from the same company. Measurements were carried out to a nominal accuracy of 0.00 1 cm-’ using a calibrated confocal etalon with a FSR of 0.009811 cm-’ in conjunction with accurately measured absorption lines. The spectral range searched extended from 1200 to 1560 cm-‘. Absolute wavenumber calibration was carried out using accurately known absorption lines of SO1 [ 29 1, NzO [ 301 and formaldehyde [ 3 11. The diode laser beam was passed axially through the cell onto a HgCdTe infrared detector. Signals were processed by source modulation of the diode laser at 8 kHz followed by phase sensitive detection.
4. Spectra and analysis Two examples of the septet pattern displayed by all the lines of MnH are given in figs. 1 and 2. These figures show respectively the P( 7) and R( 5) tran35
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1405.70
CHEMICAL PHYSICS LETTERS
1550&l .M)
1405.90
1550.90
cm-’
cm-f
Fig, 1. The P( 7) transition of the fundamental band of MnH in its ground electronic state. The septet structure arises from the couplingof the spin of the six unpaired electrons (S=3) with the overall motion. The relevant values of S are indicated above each component. In the P-branch transitions the most intense component, with &IV+ 3, is positioned at the low frequency end of the pattern. The upper trace shows the interference fringes from the calibration Won, which has a FSR of 0.0098 cm-‘. The individual components are separated by approximately 0.035 cm-’ in this case. Time constant 30 ms.
sitions of the fundamental band. As can be seen, in the P-branch transitions (fig. 1) the strongest line, which corresponds to J=N+ 3, is at the low frequency end of the pattern, whereas in the R-branch (fig. 2) the intensity pattern is reversed. At first sight, the patterns shown in figs. 1 and 2 appear to display a regular frequency spacing, as would be expected as a result of the presence of only spin-rotation coupling. However, closer inspection reveals that the separations between the seven individual spin-rotation components are not exactly the same. Slight variations are present as a result of the spin-spin coupling. The data obtained are shown with their assignments in table 1. As can be seen from these data the observed hyperfine pattern was less widely spaced in the R-branch than in the P-branch and this effect increased with increasing vibrational excitement. As a result, the R ( 18) transition of the v=3t2 band was 36
3 November 1989
Fig. 2. The R( 5 ) transition of the fun&mental band near I55 1 cm-‘. The most intense component it at the high frequency end of the septet battern in the R-branch transitions. In this case the components are separated by approximately 0.02 cm-‘. Time constant 30 ms.
observed as a single broad line. The predicted spinrotation splitting between the individual components was only of the order of 1F3 cm-’ in this case. The data of table 1 were fitted to eq. ( 1) and the residuals are shown in parentheses in table 1. The parameters fitted and the values obtained are shown in the first column of table 2. The results obtained by Nevin [4] for some of these parameters are included for comparison.
5. Discussion As can be seen from table 2, the present work has greatly improved the accuracy of the ground state parameters of MnH and almost all of the higher-order parameters have been determined for the first time. This is particularly true of the vibrational parameters for which only approximate values were previously available. Nevin’s data [ 41 on the A 711+X ‘2 emission band of MnH was reanalysed at a much later data by Pacher [ 25 ] and again by Kovacs and Pacher [ 26 1. However, we have chosen to list mainly Nevin’s
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original data from 1945 in table 2 since these are generally in better agreement with the present work and there seem to be some inconsistencies in the resuit of ref. [ 261.
3 November I989
As can be seen from table 2, Nevin’s values [ 41 for the rotational parameters B, ( Yo,), D, ( Yaz), and (Y, (Y,,) are in admirable agreement with the results from our accurate measurements. This may, how-
Table 1 Observed transitions of manganese hydride. Number in parentheses represent obs. -talc. in units of the last digit Transition (cm- ’) rklc0
Transition (cm-i)
0 1 2 3
1405.9167( - 18) 1405.8841(-00) 1405.8475( -07) 1405.8107(-03) 1405.7729( -03) 1405.7353 (-02) 140X6994( 07)
P( 6) P( 6)
S= S=
8) 8) 8) 8) 8) 8) 8)
s=-3 s= -2 IS=-1 s= 0 s= 1 s2 s= 3
1392.6532(-14) 1392.6184(-10) 1392.5816(-12) 1392.5457( 04) 1392.5072( 00) 1392.4701( 09) 1392.4321( 04)
P( P( P( P( P( P( P(
5) 5) 5) 5) 5) 5) 5)
S=-3 s=-2 SE--l s= s= s= s-
9) 9) 9) 9) 9) 9) 9)
s=-3 s--2 Is=-1 s= s= s= SF
0 1 2 3
1379.1244(-17) 1379.0903( 01) 1379.0524( -08) 1379.0148( -04) 1378.9768( 00) 1378.9390( 06) 1378.9013( 09)
P( P( P( P( P( P(
4) 4) 4) 4) 4) 4)
P(l0) P(l0) P(l0) P(10) P(l0) P(l0) P(l0)
s--3 s=-2 s=-1 s= s= s= s=
0 1 2 3
1365.3414( 11) 1365.3037(-01) 1365.2681( 19) 1365.2277( -02) 1365.1904( 12) 1365.1512( 08) 1365.1130( 11)
P(l1) P(l1) P(ll) P(l1) P(l1) P(l1) P(l1)
s=-3 s=-2 s=-1 s= s= s= s=
P(l7) P(17) P(17) P(17) P(17) P(17) P(17)
s=-3 s=-2 s=-1 s= s= s= s=
P( P( P( P( P( P( P(
7) 7) 7) 7) 7) 7) 7)
s=-3 s=-2 SC-1 s= s= As= .s=
P( P( P( P( P( P( P( P( P( P( P( P( P( P(
2 3
1418.7303( 1418.6955(
0 2 3
1431.6244( 04) 1431.5931( 10) 1431.5581( 07) 1431.5221( 14) 1431.4831( 02) 1431.4450(-05) 1431.4098( -05)
s=-2 s=-1 s= ss= s-
0 1 2 3
1444.0233( 13) 1443.9895( 12) 1443.9517( 04) 1443.9126( 01) 1443.&X720( 25) 1443.8375( -28)
P( 3) P( 3)
s= s=
2 3
1456.0095( 02) 1455.9754(-11)
0 1 2 3
1351.3027(-15) 1351.2656(-16) 1351.2284(-08) 1351.1907( 02) 1351.1514(-01) 1351.1130( 07) 1351.0738( 03)
P( 2) P( 2) P( 2)
s= s= s=
1 2 3
1467.9094(-19) 1467.8456( 39) 1467.8086( -25)
0 1 2 3
1262.2289( 19) 1262.1874(-05) 1262.1483( 00) 1262.1085( 03) 1262.0679( 00) 1262.0271(-03) 1262.9857(-13)
R( R( R( R( R( R( R(
S=-3 S=-2 S=-I S= S= S= S==
0
1550.7949( -07) 1550.8195(- 18) 1550.8469( -03) 1550.8740( 09) 1550.9005( 18) 1550.9242( 08) 1550.9478( 13)
5) 5) 5) 5) 5) 5) 5)
1
I 2 3
03) 15)
37
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3 November 1989
Table 1 (continued) Transition (cm- ’)
Transition (cm-‘) v=2t-1
~~3-2
7) 7) 7) 7) 7) 7) 7)
s=-3 S=-2 s=-1 s= s= s= s=
P(l4) P( 14) P(l4) P(l4) P(l4) P(l4) P(l4)
SE-3 s=-2 s=-1 Is= s= s= s=
P(l5) P(15) P(l5) P(l5) Ul5) P(l5) P(l5)
s=-3 s=-2 s=-1 s= s= s= s=
Pt P( Pt w Pt P( Pt
8) 8) 8) 8) 8) 8) 8)
s=-3 s=-2 s=-1 s= s= Is= s=
WlO) P(lO) P(lO) P(lO) P(lO) WlO) P(lO)
s=-3 s=-2 s=-1 s= s= s= s=
P(ll) P(ll) Wll) P(ll) Wll) P(ll) P(ll)
s=-3 s=-2 s=-1 s= s= s= s=
P( P( P( w P( P( P(
0 1 2 3
1350.0734( -01) 1350.0408( 10) 1350.0047( 03) 1349.9681( 05) 1349.9305( 03) 1349.8942( 14) 1349.8570( 07)
2) 2)
s=-1 s= 0 s= 1 s= 2
1463.2900( 07) 1463.3176(-32) 1463.3533( - 16) 1463.3892( 19)
0 1 2 3
1253.7035( 09) 1253.6629( - 16) 1253.6255( 00) 1253.5861( 01) 1253.5450( - 11) 1253.5054( -06) 1253.4648( - 11)
R(ll) R(11) Wll) Rtll) R(11) Rtll) Nil)
s=-3 s=-2 s=-1 h-0 s= 1 s= 2 s= 3
1535.5121( 08) 1535.5289( 05) 1535.5447( -02) 1535.5598( - 10) 1535.5747( - 12) 1535.5898( -04) 1535.6031(-05)
0 1 2 3
1238.9525( 08) 1238.9138( 07) 1238.8749( 10) 1238.8351( 10) 1238.7941( 02) 1238.7534( -01) 1238.7118(-14)
R(14) R( 14) R(14) R( 14) R( 14) R(.l4) R(14)
s=-3 s=-2 ..%-I s= 0 s= 1 s= 2 s= 3
1552.3491( 18) 1552.3607( 08) 1552.3719( 01) 1552.3819(-09) 1552.3922( -09) 1552.4025 ( 00) 1552.4117( 06)
0 1 2 3
1279.6148( -04) 1279.5817( 04) 1279.5461( 03) 1279.5089( -02) 1279.4711(-06) 1279.4342( 00) 1279.3979( 05)
P( P( P( P( P( P(
7) 7) 7) 7) 7) 7)
s=-2 s=-1 s= s= s= s=
0 1 2 3
1292.3069( -02) 1292.2717( -06) 1292.2358( -03) 1292.1986( -05) 1292.1620( -01) 1292.1273( 13)
0 1 2 3
1253.3219( -14) 1253.2863( - 14) 1253.2494( - 16) 1253.2121(- 12) 1253.1757( 07) 1253.1356( -09) l253.0974( -09)
R R R R R R
(4) (4) (4) (4) (4) (4)
s=-2 s=-1 s= 0 s= 1 s= 2 s= 3
1420.3590( -03) 1420.3850( 11) 1420.4086( -03) 1420.4334( -04) 1420.4587( 13) 1420.4808( 22)
0 1 2 3
1239.7694( 1239.7330( 1239.6954( 1239.6576( 1239.6193( 1239X03( 1239.5417(
R( R( R( Rt R( R( R(
5) 5) 5) 5) 5) 5) 5)
s=-3 s=-2 s=-I s= s= s= s=
0 1 2 3
1428.7556( 04) 1428.7782( -01) 1428.8009( -08) 1428.8234( - 16) 1428.8475 ( -04) 1428.8693( -04) 1428.8901( 04)
s=
0
1500.3247( -02)
08) 07) 04) 08) 12) 11) 13)
R( R( R( Rt
2) 2)
R(18)
ever, be a little pilation, Huber rected values agreement with 38
fortuitous, since in their data comand Herzberg [ 321 published corwhich are in slightly less good our values.
The present work seems to show no evidence that the ground state of MnH displays any unusual effects arising from the perturbations discussed by Kovacs and Pacher [ 261. This may be due to the fact that
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Table 2 Parameters determined for manganese hydride (cm-‘). Numbers in parentheses represent one standard deviation in units of the last digit This work
Y10 Y20
Nevin [4]
Y,,XlO Y,,X 105 Yj,X104 Y0,X lo4 Yl2X 106 Yz*x 106 Y03x lo9 YOlx 102 YIIx 104 hlX 10S Yozx 106 co*x 103 &X lo4
1546X536(15) -27.60280(91) -3.0822(15) 5.685795(37) - 1.60488(22) 4.05(91) -3.255(13) -3.0630(30) 2.983(68) -1.201(16) 8.68(60) 3.2055(83) -8.32( 13) -3.40(33) -7.54(21) -2.234(82) -1.30(18)
‘) Ref. [S].
“Ref. [25].
Y,,x 10
yo,
64
&&
1548.0 a> 28.8 a)
& ol,XlO
5.68548 1.6079
0,x
10’ B,x lo6
3.03 15 1.46
Hex lo9 Yc
9.10
yD,x lo6 cxlO3
3.13
-6.;(4) -4.0
3 November 1989
patterns extend over only 0.2 cm-’ at most, the peak height of the signals observed should have a fair correlation with the intensity variation of the individual components within a transition. The intensity pattern of the P( 7) transition shown in fig. 1 is in reasonable agreement with the expected pattern, whereas the R( 7) (fig. 2) agree far less well. The main feature expected of the relative intensities is that they should increase with increasing magnitude of J. This was generally observed, but the expected detailed behaviour did not always appear to be present. Further discussion of this problem will require better relative intensity measurements than are available at the moment.
Acknowledgement b,
our data does not include transitions with such high values of the rotational quantum number as those measured by Nevin [4], but all that can be said at present is that the ground state of MnH appears to be quite “normal”. With the exception that two spinspin parameters (eol and a rotational correction term ~~~~were introduced, the fitting of the data of table 1 required no more variables than were used in our analysis of the spectra of several ‘C molecules [ 11,12,16,17] _Indeed, in the cases of ZnH and CdH [ 171, due to the presence of strong anharmonicity, more parameters were required than were used here for MnH (e.g. five y parameters compared to the four used here) _ Relative intensities. The relative intensities of the individual hyperfme components would be expected to be similar to that observed in comparable situations with the coupling of nuclear spin to overall molecular rotation and S-L coupling in an atom. For these cases, the relative intensities have been tabulated in numerous textbooks (e.g. ref. [ 33 1). Intensities cannot be determined very accurately from diode laser spectra since the output power of the diode varies across the mode. However, since the
This work is supported by the Deutsche Forschungsgemeinschaft. The authors wish to thank U1rich Magg for his aid with the programming and for helpful discussions.
References [ I] T. Heimer, Naturwissenschaften 24 ( 1936) 52 1. [ 21 A.G. Gaydon and R.W.B. Pearse, Nature 139 ( 1937) 590. [ 31 T.E. Nevin, Proc. Roy Irish Acad. 48 (1942) 1. [4] T.E. Nevin, Proc. Roy Irish Acad. 50 (1945) 123. [5]T.E.NevinandP.G.Doyle,Proc.RoyIrishAcad.52(1948) 123. [ 61 T.E. Nevin, M. Conway and M. Cranley, Proc. Phys. Sot. (London)A62(1952) 115. [ 71 T.E. Nevin and D.V. Stephens, Proc. Roy Irish Acad. 55 (1953) 109. [S] W. Hayes, P.D. McCarvill and T.E. Nevin, Proc. Phys. Sot. (London) 70 (1957) 904. [9] U. Magg and H. Jones, Chem. Phys. Letters 146 ( 1988) 415. [ 101 U. Magg and H. Jones, Chem. Phys. Letters 148 ( 1988) 6. [ 111U. Magg, H. Birk and H. Jones, Chem. Phys. Letters 149 (1988) 321. [ 121U. Magg, H. Birk and H. Jones, Chem. Phys. Letters 15 1 (1988) 263. [ 131U. Magg. H. Birk and H. Jones, Chem. Phys. Letters 15 1 (1988) 503. [ 141 R.-D. Urban, U. Magg and H. Jones, Chem. Phys. Letters 154 (1989) 135. [ 151A.H. Bahnmaier, R.-D. Urban and H. Jones, Chem. Phys. Letters 155 (1989) 269.
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[ 161 R.-D. Urban, A.H. Bahnmaier, U. Magg and H. Jones, Chem. Phys. Letters 158 (1989) 443. [ I 7 ] R.-D. Urban, U. Magg. H. Biik and H. Jones, J. Chem. Phys., to be published. [ 181 H. Birk and H. Jones, Chem. Phys. Letters 161 (1989) 27. [ 191 N.N. Haese, D.J. Liu and R.S. Altman, J. Chem. Phys. 81 (1984) 3766. [20] B. Lemoine, C. Demuynck, J.L. Destombes and P.B. Davies, J. Chem. Phys. 89 (1988) 673. [ 211 C. Yamada and E. Hirota, J. Chem. Phys. 88 ( 1988) 6702. [ 221 W. Urban et al., Spring Conference of the German Physical Society, Essen (March 1989). [23] J.M. Brown, private communication. [24] F. Hund, Z. Physik 43 ( 1927) 805.
40
3 November 1989
(251 P. Pacher, Acta Phys. Acad. Sci. Hung. 35 (1974) 73. [26] I. Kovacs and P. Pacher, J. Phys. B 8 (1975) 796. [ 271 I. Kovacs, Rotational structure in the spectra of diatomic molecules (Hilger, London, 1969). [ 281 J.L. Dunham, Phys. Rev. 41 ( 1932) 72 1. [ 291 G. Guelachvili, O.N. Ulenikov and G.A. Yshakova, J. Mol. Spectry.108 (1984) 1. [30 ] G. Guelachvili and K.N. Rao, Handbook of infrared standards (Academic Press, New York, 1986). [ 3 I] S. Nadler, D.C. Reuter, SJ. Daunt and J.W.C. Johns, NASA technical memorandum 100709 (1988). [32] K.P. Huber and G. He&erg, Constants of diatomic molecules (Van Nostrand Reinhold, New York, 1979). [ 331 C.H. Townes and A.L. Schawlow, Microwave spectroscopy (McGraw-Hill, New York, 1955).