The OH stretching fundamental of hydroxylamine

JOURNAL

OF MOLECULAR

SPECTROSCOPY

103, 300-3 l l (1984)

The OH Stretching Fundamental of Hydroxylamine’ M. E. COLES, A. J. MERER,’

AND

R. F. CURL

Chemistry Department and Rice Quantum Institute, Rice University, Houston, Texas 77251 The OH stretching fundamental of hydroxylamine, Yi, has been studied using a computercontrolled color center laser spectrometer. Absorption and Stark-modulated spectra of this AC hybrid band were obtained in the spectral region from 3630 to 3710 cm-‘. The spectrum is dominated by many strong perpendicular c-type Q branches, but both parallel and perpendicular type transitions are observed. The rotational structure has been fitted by least squares, and rotational and centrifugal distortion constants have been obtained for both states. The excited state exhibits many small perturbations. All lines observed are believed to originate from the tram form of hydroxylamine and no evidence for the cis isomer was found. Transitions belonging to a hot band, in which the low-energy torsional motion is excited in both the ground and upper states, have been located and assigned. I. INTRODUCTION

Low-resolution infrared spectra of gaseous and solid hydroxylamine, a relatively simple but unstable small molecule, were first observed in 1952 by Giguere and Liu (1) and then by Nightingale and Wagner (2). Although we will have little to say concerning this, it is worthwhile noting that the interest in hydroxylamine from experimental and theoretical points of view has been the establishment of its equilibrium conformation. NHzOH possesses the unique distinction of being the simplest molecule with different numbers of lone pairs on adjacent atoms. Ab initio studies by Pederson and Morokuma (3) and by Fink et al. (4) have given the relative cis to tram energy as 7.37 and 10.79 kcal/mole, respectively. Lombardi et al. (5), in considering the lone pair effects, speculate that interactions via the lone pair associated with the oxygen tend to stabilize the cis form of NH20H, resulting in a cis to trans energy difference of only 0.7 kcal/mole. Giguere and Liu (I) noted apparent doublings of some NHIOH bands and attributed this to the existence of both cis and trans isomers. However, in 1972, Tsunekawa (6) analyzed the microwave spectra of hydroxylamine, obtained the ground-state constants, and found only the trans isomer to be present. Infrared studies of the torsional fundamental by Tamagake et al. (7) also indicate the existence of the trans isomer only, although they could not rule out the possibility of a higher energy cis isomer. Perhaps because of its instability, little high-resolution work has been done on NH20H. We have utilized a computer-controlled color center laser spectrometer, ’ This work was supported by National Science Foundation Grant CHE 82-OOO96and Grant C-07 I of The Robert A. Welch Foundation. ’ On sabbatical leave from Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Y6, Canada. 0022-2852184 $3.00 Copyright Q 1984 by Academic Press. Inc. All ri&ts of npmduction

in any form reservd.

300

OH FUNDAMENTAL OF NHzOH

301

developed recently (8), to study the ro-vibronic levels of the fundamental OH stretch to improve the ground-state constants and to obtain constants and information on the vibrationally excited state (v,) as well as look for any evidence of the cis isomer. II. EXPERIMENTAL DETAILS

The apparatus used to study the vl vibration of NH*OH is shown in Fig. 1. A Burleigh FCL-20 color center laser using a Li:KCl crystal was pumped with 2 W of 5 14.5~nm laser light from a Spectra Physics 17 1 argon ion laser. The color center laser was scanned continuously under computer control (8) utilizing a DEC 1 l/23 minicomputer with feedback control and calibration provided by acquisition of the output of a set of diagnostic elements, consisting of two spectrum analyzers, a temperature-compensated marker cavity, a reference gas absorption cell, and a reference power detector. With this apparatus, high-resolution absorption spectra of NHzOH were obtained with the 2-m multipass White cell operating at 20 passes. Stark modulation spectra were also obtained simultaneously utilizing an 80-cm Stark cell with a plate separation of 3 mm and modulating with 500 V amplitude 100 kHz square wave. Signals from the marker cavity, reference cell, and signal channel were acquired and simultaneously stored by the computer, providing a monitor of scan stability and a means of frequency calibration. Frequency calibration of observed spectral lines was done interactively, using a set of computer programs developed for this purpose. When not limited by the accuracy of calibration lines used, the observed spectral features could be measured to 0.001 cm-‘. Hydroxylamine was prepared using the method of Lecher and Hoffinan (9). Sodium ethoxide was added dropwise to hydroxylamine hydrochloride suspended in absolute ethanol, using bromyl blue to indicate the endpoint of the titration. Solid sodium chloride was filtered off and the liltrate was then cooled in a refrigerator to obtain long white needles of solid NI-I*OH. The hydroxylamine crystals were filtered, washed with anhydrous ether, and stored in a freezer under argon until needed. It was found that hydroxylamine, while chemically unstable under air at room temperature, is quite stable when stored under argon at low temperatures (-5’C). Kr’ w Ar’

Ion Loser

TO Computer

FIG. 1. Color center laser spectrometer used in the investigation of the ro-vibronic transitions associated with the OH stretch fundamental (Y,) of hydroxylamine.

302

COLES, MERER, AND CURL

Hydroxylamine was sublimed into the White and Stark cells of the spectrometer at room temperature. The sample was flowed continuously through the cells with the pressure maintained at 100 mTorr using a throttling valve on the vacuum pump. These conditions resulted in strong NH20H signals in both channels and provided adequately for removal of the decomposition products (ammonia and water). III. OBSERVATIONS

The OH fundamental of hydroxylamine exhibits a classic near prolate rotor spectrum which is dominated by many strong c-type (perpendicular) Q branches. A good example is the ‘Q4 subbranch shown in Fig. 2. A slightly closer inspection reveals the presence of strong u-type as well as c-type lines. Preliminary assignment proved to be straightforward as an unambiguous assignment could be obtained from the separation of the Q branches from their respective P or R transitions. Stark modulation was found to be especially helpful in picking out the low J transitions in both the c-type Qbranch lines (Fig. 2) and the u-type lines. The lo-cm-’ segment in Fig. 3 illustrates the usefulness of Stark modulation in pulling out the low-J members of a subband. In NH*OH Stark modulation affects levels with J - K for K > 0 through the p. component of the dipole moment, and certain levels with low K that happen to lie close to other levels differing by one unit in both K and Jthrough the p= component: we have observed both types of Stark effect in one spectrum. Combination differences provided a useful check of the correctness of the assigned lines and aided in the assignment of low-J Q lines, where crowding or asymmetry doubling made assignment difficult. Intensity measurements of parallel and perpendicular type lines provide the ratio of parallel to perpendicular transition moments. From this ratio, the angle that the transition moment makes with the a axis was calculated to be 55.6 f 3.0”. Choosing the sign which makes the transition moment most nearly parallel to the OH bond, the angle between the transition moment and the OH bond was found to be 18 & 3”, with the transition moment tilted toward the a axis. All lines assigned originate from the tram form of hydroxylamine, and unfortunately no evidence for the cis form was found. The assigned lines are listed in Table I.

Marker

FREO

(cm-’

)

FIG. 2. Portion of the hydroxylamine spectra showing the perpendicular ‘Q., subbranch.

303

OH FUNDAMENTAL OF NHzOH

x 3678 0

,

3674 0

3676 0

FREO

absorption

3672.0

3670 0

Ccm-‘)

FIG.3. The IO-cm-’ segment of the hydroxylamine spectra. Stark modulation was helpful in simplification and designation of members of a subbranch.

IV. FITTING OF NH20H DATA

Initially we attempted to fit the spectrum using Watson’s A-reduced rotational Hamiltonian (20); however, because of the nearness of hydroxylamine to a prolate rotor, the splittings observed in the K = 2 levels could not be obtained in predictions using this Hamiltonian. Therefore, Watson’s S-reduced Hamiltonian (10) was used to fit the spectrum. Specifically we took H = [‘4 - (B + C)/2]JZ + %(B + cy2 -

+

‘/4(B

-

c)(J:

+

_P)

D.,J4 - DJKJ2J: - DKJ;f + d, J*(J: + J!) + d,(J4, + 54)

where Jk = Jb T iJ,. It was soon realized that there were several small but definite perturbations, which were biasing the fit. Therefore, upper-state energy levels were obtained using the ground-state combination differences and the assigned lines, thereby mapping out the upper state and allowing all perturbations to be located. Because the perturbations were small and, for the most part, localized, a weighted nonlinear least-squares fit was performed simply omitting the perturbed lines. Where perturbations prevented inclusion of certain lines in the fit, combination differences of those lines were included, with appropriate weighting, so that the information they carried about the groundstate constants would not be lost. The microwave transitions (6) were included in the fit with appropriate weighting (X200). A weighted, nonlinear least-squares fit of 689 data points resulted in the groundand excited-state constants listed in Table II. The numbers in parentheses represent estimated standard deviations. The ground-state constants agree adequately with earlier microwave work by Tsunekawa (6) as would be expected, since the microwave lines were included in the fit with large weights. With these constants it was then possible to predict unperturbed lines to about 3 X 10e3 cm-‘. Additional lines (perturbed and unperturbed) were then assigned, resulting in a total of over 1100 assigned lines. The maximum K”, of assigned lines is 9 and the maximum J is 29. These lines are listed in Table I.

304

COLES, MERER, AND CURL TABLE I Assigned Lines of the NH20H OH Stretching Fundamental

3a3.947 3625.628 3627.218

c

OH FUNDAMENTAL

305

OF NH20H

TABLE I-Continued

%(I) 0

: : 5 : 6 9 10 11 II 13 1. 1, 1‘ 11

3‘5~.,‘7 ,‘53.1.3 3‘5..,11 3‘5‘ 591

3‘55.P3, ,‘51.‘0( 3‘59.17. 5“0.,,1 ,“I.‘OI 3“. 2‘. 3‘65 .XU 3“l.J74 3“9.231 3‘10.6‘1 3‘11.519 3‘1..1,‘ 3‘15.‘,, ,‘ll..,7 3‘79.0,, ,“0.,1‘ 1‘62.35, 3*,3.**1 3‘” .‘10 3“,.230 3‘13.U. 3‘90..,0 3‘91 .Q.,

3‘5‘:ml

5*59.9*9 3‘61.593 ,“,.1,‘ 3“..910

3“‘;,l‘

3“3,1,3 3“9.,ll 3‘11.540 ,‘1,.1‘* 5‘14.135 ,‘l‘..1l 3‘7‘.11‘ ,‘l9.7,.

,‘,‘.105 ,‘,,.,“ 3‘61.450 ttr3.on 3“..l,1 3“‘..ol 3‘66.060 ,“9.,10 ,*1*.3,1 3‘13.001 3‘1. .‘.. ,‘l‘.IP 3‘77.913 3‘79.5,. 3‘31.1,, 3“2.‘19 3“. ..,‘ 3“‘.P,5 3“,.“5 5‘69.1”

=

’

:

1‘ I, 1* 19

::

::

:: :: I‘

3“6.,“ f“‘.l59 3‘66.13, 3“‘.,1, ,“‘.,00

5‘5,.311 3‘55.19, ,‘I, 2,. 3‘,,.15. ,‘,5.1,0 ,‘,5,101 3‘,,.1‘. ,‘,,.I30 ,‘,,.093 3‘55.0,‘ ,655.Ol, 3‘,..9,5 3‘5..931 1‘,..3‘5 1‘54.335 ,‘5..,,3 3‘,..‘91 ,‘,..‘.9 ,‘,..5‘1 3‘,...‘1 ,‘,..,‘A

3*,*.*5* 3‘,‘.‘., ,‘,‘.‘3‘ 3‘,‘.‘x! 3‘16.301 ,‘,‘.,3. 3‘,‘.,‘3 3‘,‘.7,9 3‘,‘.,13 3‘,‘.“, ,‘,‘.‘,f 3‘,‘.‘1‘ 3‘76.593

3“‘;01,

=

c c c c

3“‘.0., 3“‘.013 3“,.9‘. 3‘65.94, 3‘65.911 3“5,“‘ 3‘65 .‘I9 3“,.,,1 3“5,,,9 3‘6, .‘I. 3‘65.6vl 3“,.,., 3“5.‘78 1“5..09 5“,.3,1 1“,.1,Z 3‘6, ,166

,*,*.,a

5‘,‘.,5, 3‘76.52, %,‘..,, %,‘..., 3‘1‘..00 3‘,‘.,,1

3‘76.51‘

c

3‘,‘.512 5‘,‘..5, 3‘,‘..12 3‘1‘.,“ 3‘,‘.3,9 3‘,‘.15,

3‘3,.‘93 36‘5.~9‘ 3‘84.m. 36.1 .‘W l‘30.913 ,‘,S.Pll 3‘7,.50‘ 3‘15.615

e

3‘,..10, 3‘71.399 3‘70.69. ,“,.*39 ,“7.1,9

3‘,2.‘.1 3‘91.1.. 3“9...3 3“1.,.5 ,*1*.03* 3‘“.53, 3‘81.619

3‘59.6‘0 3‘61.33, 3‘63.000 3“..‘55 36‘6.501 56‘7.941

,tr,.,n

5‘11.12, ,‘7~.‘~~ ,‘,..,,0 3‘76.110 3‘77.79, ,*,9..3* 36‘1.050 ,662 .‘09 1‘”

c 36‘0.15. 3‘61.909 36‘3.5‘1 3‘65.113 - J“‘.3‘* 36‘6.50‘ 3‘1P.1.9 3‘,1.7“ ,‘1,..,, 3‘15 .O“ 3‘1‘.‘8l 3‘,‘.311 3‘,9.~3, D 3‘81.519 36‘3.19‘ ,‘“.‘1.

3“2.mb~

;::;$;b< 5“,:1‘1 3‘66.909 3‘70.530 c

c c c c

,‘71.199b ,613 84’

c 3‘15:.ll~~ 3‘,,.OW 3‘1‘.713

3“0.327b

.l‘l~C

::g::$

3‘~0.0*3

;:~-$c 3‘94.0‘3

3‘17.30‘ 3‘1,.‘l, 3‘,3.920 3‘11.11‘ 3‘,0.,,0 3‘61.631 3‘61.130 ,665 ..I* 3“3.,11 3“1.0~, 3‘60.11, 3‘,‘.‘,, 3‘56.90,

c

3‘56.9,‘ ,“0.‘,‘ 3**1.1* 3“3.P,, 3‘65.607 3‘61.2‘1 3“‘.,09 3‘10.5,‘ 3‘11.1,9 3‘13.641 ,‘1,..1‘ 3‘11.123 3‘76.155 3‘10.311 ,682 .WI 3‘63.619 ,“5.I.l 3‘66.859

~~:~$~~bc 3‘89:‘10b

3‘91.2,P

‘

3102.905~ 3,01.13‘b’ ,‘W.,O, 3*91.,9* ,‘9‘.W1 3‘94.3“

~f”..O’ 36‘7.3“

l.W.1‘1

3“,.3,1 3‘1,.,,, 3“,.33, 36‘1.31‘ 36‘1.195 ,‘37.1,1 ,“,.1., 36‘1.1,‘ 3“,.11, 3‘,,.1*, 3‘11.10, 3‘67.c.e‘ 3‘6l.o.5 3‘,,.001 3“‘*95, 3‘66.911 3“‘.‘,9 36U.79, 3“‘.1‘, 36‘6.10~ 3“‘.‘.,

3‘9,.,., 3‘91.131 ,‘W.ll. ,‘9,.‘92 3‘9,.‘,1 301.‘. ,‘.,.‘I9 ,‘9,.,Sl 3‘9,.,5‘ 3‘91.52. ,‘,,..)o ,‘,,..., ,‘,,..I0 36W.3‘5 ,‘,,.,I9 16rl.111 3‘,,.11. .5‘9,.11@ 3‘91.11, 3‘9,.05, 3‘96.91, 3‘9‘ .907 1‘94.633

3107.9‘1 3,0,.,“ 3,0,.9.‘ ,,O,.SM ,,o, .901 5107.6‘0 ,rm 3.1 5107.11‘ 3,0,.,‘. no, .I.‘ 310,.,,1 ,lW.“9 ,lW.‘% ,707 .,I ,,o,.,,l ,,ol..** 3m,..3.

,,m.,u 5,0,.31‘

371‘.Ol, 3716.003 ,,1,.9,‘ 3117.9‘1 3,1,.,1, ,,I, 300 3,1,.“‘ ,,I,.‘*, ,,I,.,‘.

,111;“. ,,1,.*.z ,tl,.‘u 3,~,.‘31

nn.,,,

VI11 .,I2 3,*1.“‘ 3,11.“I ,1*1.*31 ,rn.rol 3,m .,‘l 311,.,33 = ,711 .‘W - 3,2,.‘,1 ,,W.‘~, ,,*,.5,1

c

,n,.,z. 3,1,..,1 5,1,..21 ,,2f.,‘. ,,1,.30. 3,1,.3.9 ,,I,.,‘, 3,1,.110

,,,,.‘d 3131.5‘. ,,,,.,,‘

,,,,.%n

c

313, ..,,

n,,..,, 3,,7..**

3131.3‘.b’ ,,3,.,.1,*

:;;;*:g*e ,,n:roob

3m.d 3131.011~ :;;:*;;bG

m‘:‘d

306

COLE& MERER, AND CURL TABLE I-Continued

V. PERTURBATIONS

As indicated previously, the excited OH stretch of hydroxylamine exhibits numerous small perturbations. Usually the existence of a perturbation could be confirmed with several transitions. As described above the rotational constants were determined by fitting unperturbed lines, and then the observed minus calculated frequencies for a fixed K value were plotted versus J(J + 1) to locate the perturbations. These graphs are shown in Fig. 4. It is not surprising that the hydroxylamine spectrum contains many perturbed lines, as NHzOH possesses several low-energy vibrational modes, the overtones and combinations of which can interact with the vI vibrational mode and cause shifts in line positions. All but one of the fundamental mode frequencies for NH20H are known from previous work (I, 2, 7) and are listed in Table III. Guessing a value for the NH2 twist (Q) and taking all possible combinations into account in the region from 3600 to 3700 cm-‘, one finds several possibilities for interacting levels. These are listed in Table III with their resulting symmetries. There is some uncertainty about the precise energies of these combinations as anharmonic constants are not known and have not been taken into account. Because vI is of A’ symmetry, the interacting levels divide themselves into two groups which can interact only by Coriolis coupling (A” vibrational symmetry) or by both Fermi and Coriolis (A vibrational symmetry) type coupling. Most of the perturbations seem to be of the Coriolis type, because they exhibit a J dependence in which the levels for J values above the onset of the perturbation continue to be shifted. This effect is seen at high J(J - 23) in the K = 1, 2, and 3 stacks. Unfortunately all the perturbations are small (the largest shift is -0.1 cm-‘) and are localized in that they cannot be followed from one Kstack to another. This makes obtaining definite information about the unseen levels causing the perturbation extremely difficult especially in view of the lack of information concerning the anharmanic constants of hydroxylamine.

OH FUNDAMENTAL

OF NHzOH

307

TABLE II Rotational Constants for Hydroxylamine (cm-‘) Ground st.te

Excited state

A"

=

6.370290(14)'

A'

=

6.29676(4)

B"

=

0.8412084(19)

B'

=

0.839757(14)

C"

=

0.8391326(18)

C'

=

0.838756(14)

D;

=

2.525(7)E-6

=

2.594(9)E-6

D;

D;'p=

2.202(14)E-5

D;K =

2.153(13)E-5

Di

l.l92(13)E-4

=

l.l76(ll)E-4

=

Di

d:' = -4.21(19)&E

d:

=

Z.l(ZO)E-8

d;

d:

=

5.60(31)E-8

=

5.18(19)E-8

3.=3649.8861(4)

Microwave vsluesb A" = 6.370311 B" = 0.8412376 C" = 0.8391051

%c

uncertainties quoted are one estimated standard deviation.

bRef 6.

VI. NH,OH

HOT BANDS

Hydroxylamine exhibits another weaker set of perpendicular type Q branches 5 cm-’ displaced to lower frequency from the strong perpendicular (c-type) Q branches. These are assigned as being due to hot bands of hydroxylamine, in which a lowfrequency fundamental (vg) is excited in both the upper and lower states. The lines observed by Giguere and Liu (I) at 1115 cm-‘, which they thought to originate from the cis isomer, are probably also of this type. It is felt that these lines are hot bands of the trans form of hydroxylamine rather than the cis isomer for several reasons. Neglecting centrifugal distortion and higher effects, and assuming that the ground-state constants are approximately equal to the upper-state constants, the relative spacing between perpendicular type Q branches is -2[,4 - M(B + C)]. From their geometries, one can calculate the ground-state constants for the cis and trans isomer (see Table IV) and predict that the relative spacing between Q branches in the cis isomer should be 0.4 cm-’ smaller than in the trans. However, the difference in the average spacing in the weak Q-branch series and the strong one is only 0.01 cm-‘. Giguere and Liu (I) noted a similar situation in the spacing of the rotational structure in the 1115cm-’ band, but felt that their measurements were not sufficiently accurate to be certain about this point. The intensity of these transitions compared to the vI transitions should be reduced by the Boltzmann factor for u9. This results in a calculated intensity ratio of 0.16

308

I....,

1

3,

I .,,.

/

.f..

.

I.,

~

r

L

0

I

0

~~T--.~_-

~-~.-~

200

400

600

a00

i 10Q0

J(J+1) FIG. 4. The observed minus calculated frequencies for each K value plotted versus J(J + 1) illustrating the perturbations. The asymmetry doubling components for K = 1 and K = 2 are shown with the lower energy component plotted lowest. The largest perturbations can be easily seen for K = 7 and at high J for K = 0, 1, 2, 3. Numerous smaller perturbations exist such as those which can be discerned from the figure by careful examination in K = 9 (2) K = 8 (2), K = 6 (2) K = 5 (I), K = 4 (2) K = 1 (1 in both components). Even smaller perturbations become evident when the figure is plotted on an expanded scale where the experimental scatter of the term values calculated from different transitions becomes more evident.

compared to a measured intensity ratio of 0.2, providing further support for the assignment of these lines as hot bands. Tsunekawa (6) also noted the existence of satellite lines in the microwave spectrum, with a strength of 0.18 compared to the main lines, and attributed these to excited states of the torsional vibration. The hot bands were assigned by plotting the relative spacing of the Q branches and comparing this to the relative spacings of the main Q-branch series. By comparison of line intensities and relative spacings, the weak Q branches were found to correlate with strong Q branches 5 cm-’ higher in frequency. This assignment was supported by the fact that the largest apparent splitting occurs in the weak Q branch corresponding to K” = 1. In addition, P and R lines were located and checked by combination differences. A total of 75 lines were assigned, and are listed in Table V. The hot band is expected to be even more perturbed than the fundamental as the upper state has a higher energy. As expected, a large number of perturbations were found to be present in the hot band. As there are fewer transitions observed and more perturbations expected, it was not feasible to fit all the rotational and centrifugal distortion constants of both vibrational states for the hot band. Therefore, the centrifugal distortion constants were fixed at the values obtained for the fundamental except that DJ and DJK were fixed at the excited torsional state values reported by Tsunekawa (6). The rotational constants B and C were also fixed to his microwave values. The lines assigned are

OH FUNDAMENTAL

OF NH20H

309

TABLE III NH20H Vibrational Modes (cm-‘) +, =

3650

OH

stretch

3,

= 3291

NH

symmetric

3,

= 1605

NH,

3,

= 1357

OH bend

3,

= 1120

NH, wag

3‘

= 895

NO stretch

3,

= 3350

NH asymmetric

J,

= 765

NH,

3,

= 386

torsion

Combinations

levels

the

region

3600-3700 A”

cm-’

symmetry

3,+

3,+

3,+

J,

= 3651

Q,+

3,

+,+

q,+

q,+

Q). = 3628

Q,+

q,+

N,

3,+

h),+

V,+

N,

= 3652 w,

‘+),+

69,

I!,+

h),+

3,+

J,+

M,+

‘The

in

stretch

twist?

symmetry

A’

stretch

bend

numbers of

2h),

N,

= 3659(3638)’

= 3613 a3, J,

3.

= 3682(3661Ja = 3620

9,+

9,+

Qs+

h),+

J,+

J,+

= 3683

J, w,

=3666

= 3635(3514)’ = 3615 = 3658(3597)’

= 3609

in and

parentheses

are

calculated

using

the

known

energy

‘3,.

not strongly dependent on B’-C’ so that this was fixed to the value obtained for the upper level of the OH fundamental. Thus four parameters were obtained from the hot band transition frequencies, namely, A”, A’, B’ + C’, and yo: these are listed in Table VI. The overall standard deviation of the unperturbed hot band transitions fitted was 9 X lop3 cm-‘. The value of A - (B + C)/2 obtained here of 5.488 cm-’ agrees satisfactorily with the value obtained by Tamagake et al. (7) of 5.484 + 0.005 cm-‘. TABLE IV

A” = 6.3703

A”

B”

= 0.8408

B” = 0.8481

C” = 0.8389

C” = 0.8463

2(A-f(B+C))

= 11.054

= 6.162

2(A-f(B+C))

= 10.629

310

COLES,

MERER,

AND

CURL

TABLE V Assigned

Lines of the Hot Band

a Obr. .-cb Rel.c arym. CODIP. J' 12

J" 11

12 11 13 12 13 12 14 13 14 13 15 14 15 14 3 2 4 3 5 4 6 5 7 6 8 7 9 8 10 9 4 4 5 5 6 6 7 7 883200 9 9 10 10 4 3 5 4 6 5 7 6 8 7 9 8 10 9 11 10 12 11 13 12 14 13 15 14 16 15 17 16

K' K"

ex. Ed. (F.-~)

2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3

1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2

1 -1 1 -1 1 -1 1 -1 0 0 0 0 0 0 0 0 0 0 0 0

-1 1 -1 1 -1 1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0

3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4

2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

2

X10' rt.

3681.264 -1 3680.860 10 3682.938 -6 3682.462 9 3684.613 -11 5 3684.056 3686.325 22 3685.639 -3 3676.630 -137 3618.431 -2 3680.093 -3 3681.751 -6 3683.403 -12 3685.044 -26 3686.665 -57 3688.351 -21 3671.735 3 3611.726 6 3671.699 -7 3671.676 -14 3671.647 -24 3671.603 -47 3671.603 -24 3688.892 -2 3690.553 -4 3692.212 -4 3693.861 -12 3695.511 -16 3691.143 -35 3698.887 61 3700.499 28 3702.128 15 3703.760 9 3705.392 7 3707.011 -5 3708.666 23 3710.276 9

1.00 1.00 1.00 1.00 0.00 0.00 0.00 1.00 0.00 0.00 1.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00 1.00 0.00 1.00

J' J" 5 5 6 6 7 7 884300 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 5 4 6 5 7 6 8 7 9 8 20 9 11 10 12 11 13 12 14 13 16 15 17 16 5 5 6 6 7 7 8 8 995400 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17

asym. camp.' Obs. o-cb Rel.' X10' wt. K' K" cx. gd. (cm-l) 4 4 4

3 3 3

0 C 0

0 0 0

4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

5 5 5 5 5 5 5 5

4 4 4 4 4 4 4 4

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

3682.174 -8 3682.158 -9 3682.141 -9 3682.112 -18 3682.006-102 3682.144 60 3682.085 29 3682.043 17 9 3682.003 3681.961 3 3681.909 -11 3661.909 30 3681.847 12 3700.848 -16 3702.495 -28 3704.218 40 3705.847 16 3 3707.484 5 3709.133 3 3710.774 2 3712.413 2 3714.049 3715.564 -116 3718.925 -10 3720.539 -17 3692.479 -11 3692.450 -25 3692.497 40 3692.450 13 3692.423 9 3692.405 17 3692.362 3 3692.328 0 3692.293 -1 3692.253 -4 3692.212 -6 3692.166 -9 3692.113 -17

1.00 1.00

1.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 1.00 1;oo 1.00 1.00 1;oo 1.00 0.00 0.00 1.00 1.00 0;OO 0.00 1.00 1.00

0.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

' -1 or 1 designate the lower or upper state energy component of the asymmetrypair; 0 indicates that the level is not split. b

Observations with large observed minus calculatedvalues arc consideredperturbed. The least squarer fit did not include transitionswith large residuals.

' Indicates tbe weighting nred in calculatingterm values and reflects the quality of the line. i.e. amount of blending and intensity.

VII. SUMMARY

AND

CONCLUSIONS

The OH stretching fundamental of hydroxylamine has been studied with high resolution and is found to exhibit many strong parallel and perpendicular type transitions. The existence of many low-energy vibrational modes in hydroxylamine results in numerous small perturbations. No evidence for the existence of the cis isomer was found; this is not surprising as ab initio calculations generally suggest at least a 7 kcal/mole energy difference between the cis and tram isomer (3-5) which results in a Boltzmann factor of 10-6. Transitions which were believed to arise from the cis isomer in earlier work (I, 2)

OH FUNDAMENTAL

311

OF NH*OH

TABLE VI Rotational Constants for the NH*OH Hot Band (cm-‘) Lower Stare

Upper

state

A”

=

6.326(6)

A'

=

B"

=

0.84093B8

B'+C' =

1.67353(4)

C”

=

0.834666'

B'-C' =

O.DOlb

D;

=

2.5EMa

II& =

5

1.97E-5a

=

6.254(4)

2.6E-6b

?K

= Z.15E-5b

D;i = 1.2E-4b

%

= l.2E-4b

d; = -4.2E-Sb

d;

= 2.E-8b

d: =

d;

= 5.6E-8b

S.ZE-Sb

3, = 3644.964(U)

' From ref. 6. b.

Fxrcd at value of Table II.

are now thought to be due to the hot bands v, -t vg - 4. These types of lines are observed in the present work, shifted 5 cm-’ lower in frequency with respect to the fundamental, i.e., by the amount of the anharmonic constant x19. ACKNOWLEDGMENT A.J.M. gratefully acknowledges support by the Killam Foundation through the University of British Columbia. RECEIVED:

August

29, 1983 REFERENCES

1. P. A. GIGUERE AND I.D. LIU, Cunad. J. Chem. 30,948-962 (1952). 2. R. E. NIGHTINGALE AND E. L. WAGNER, J. Chem. Phys. 22,203-208 (1954). 3. L. PEDERSON AND K. MOROKUMA, J. Chem. Phys. 46, 3941-3947 (1972). 4. W. H. FINK, D. C. PAN, AND L. C. ALLEN, J. Chem. Phys. 47,895-905 (1967). 5. E. LOMBARDI,G.TARANTINI,L.PIROLA, AND P.TORSELLINI, J. Chem. Phyx64,5229-5235 (1976). 6. S. TSUNEKAWA, J. Phys. Sot. Jap. 33, 167-174 (1972). 7. K. TAMAGAKE, Y.HAMADA,J. YAMAGUCHI, A.HIIUIUWA, AND M. Tsus01,J. Mel Spectrosc. 49, 232-240 (1974). 8. J. V. V. KASPER,~. R.POLLOCK, R. F. CURL.,JR., ANDF. K. TITTEL,Appi. Opt. 21,236-247(1982). 9. H. LECHER AND J. HOFFMAN,Ber. B55,912-919 (1922). 10. J. K. G. WATSON, in “Vibrational Spectra and Structure, A Series of Advances,” (J. R. Durig, Ed.), Vol. VI, Elsevier, Amsterdam, 1977.