Line spectra shifts in HF and in first overtone band of DF induced by HF pressure

Desai, U. G.

Gailar, N. M.

Lovell, R. J.

English

NASA Technical Reports Server

-1- 
5% 1 the First Overtone of DF Broadened by HF 
5 
U.G. "Desai, N.M. Gailar and R.J. Love11 
Department of Physics and Astronomy 
The University of Tennessee, Knoxville, Tennessee, 37916 
ABSTRACT 
The self-shifts of the lines in the fundamental of HI? from P(7) to 
R(8) and the line shifts in the first overtone band of DF when perturbed 
by HF were measured from P(7) to R(6), Pressure-induced shifts in the HF 
fundamental were studied at room temperature and at pressures of HF varying 
from 37.5 cm of Hg to 113.5 cm of H g .  
by Herget, but the estimated error 0.5 x 10 
The shifts agreed with those observed 
-4 
cm-'/cm Hg for the present 
study was about one-third of that of Herget. 
ranged from 5.48 cm of Hg to 22 cm of Hg, and total pressure of mixed 
The partial pressures of DF 
gabes ranged from 36.12 cm of Hg to 121.8 cm of Hg. 
ference and sample cells were llO°C, 12OoC, 15OoC, and 134 C. 
Temperatures of re- 
0 The shifts 
oscillate with a period of one in J and with increasing amplitude in the 
wings from R(1) to R(6) and P(3)  to P(7). The direction of the shifts is 
tha same as that found for the DC1-HC1 system and is opposite to that pre- 
dicted by the simple near-resonant dipole theory. The magnitude of the 
shifts in the present study are considerably larger than those found from 
the DC1-HC1 study. 
Index Headings: Absorption; Atmospheric optics; Infrared; Spectra. 
https://ntrs.nasa.gov/search.jsp?R=19710023696 2020-03-11T22:14:38+00:00Z
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One o’f the most interesting studies of line shifting reported in the 
2 recent literature is that of Jaffe, et al., who reported cy the pressure- 
induced shifts of DC1 due to HC1 and also on the shifts of HC1 due to DC1. 
They observed in the first overtone band of DC1 broadened by HC1 not only 
the expected J-dependence of the line shifts, but also a striking oscil- 
lation from line to line of the magnitude of the shift. 
phenomenon is due to near-resonant dipolar interaction between DC1 and HC1. 
In HC1-DC1 they found no oscillations in the shifts. Another example of 
oscillating line shifts has been discovered in HF broadened by HC1. 
They suggest this 
3 
The authors decided to study DF-KF, to see if the large oscillations 
would occur that were found in DC1-HC1 and, if so, if the simple theory 
of near-resonant dipolar interaction would correctly predict the directions 
of the oscillations. 
do occur, are large, compared t o  the DCI-HC1 case, are linear with pressure 
of broadener gas, 
The results of our study would indicate that the shifts 
and are opposite to the direction predicted by theory. 
EXPERIMENTAL METHOD 
The spectrometer, the cells, and the method of handling of the gases 
4 
used in this study are basically as reported for earlier studies. 
ever, several modifications of the instrument have since been made. A 
600-Hz chopper incorporating a tuned reference signal is used in conjun- 
ction with a phase-sensitive Princeton Applied Research Amplifier, model 
KR-8, and a Texas Instruments model FWS recorder. A Nernst-type filament 
is used as the source and the detector is an uncooled lead sulphide photo 
How- 
conductor made to order by the 
resolution of the spectrometer 
mental slit half width of 0.14 
Santa Barbara Research Corporation. The 
may be estimated from the measured instru- 
cm . The signal to noise ratio varied from 
a 
-1 
fifty to one to five to one. 
-3 -- 
A two-cell method of measuring line shifts was employed to reduce 
error due to instrumental drift. An elevator inside the vacuum housing 
brought the reference cell and then the sample cell into the beam. By this 
means the time between runs was considerably reduced from that of the single 
ce l l  method. The reduction in error in the measurement as compared to the 
one-cell method is illustrated in Fig. 1 which compares the line shifts 
measured by Herget, -- et a 1 7  in self-broadened HF (a one-cell method) with 
those measured by the authors for the same gas. The shifts measured by the 
authors are reported in Table I. The reference cell (17.8 cm) contained a 
trace of HF. The pressures and lengths in the sample cell were 37.5 cm J3g 
(17.8 cm), 76  cm Hg (1.62 cm), and 113.5 cm Hg (0.047 cm). Both cells were 
held at room temperature, 24OC - + 2OC. The mean deviation calculated for 
this study, 0.5 x 10’4cm-1/cm Hg, is about one third of that reported by 
Herget. The agreement of the results of the two studies is quite good, 
however . 
Gas, whether DF or HF, was admitted to the cell open to the manifold at 
room temperature. The cell-manifold pressure was then read on a Bourdon 
gauge. Subsequently, the cell was closed, heated to temperature, and a run 
was made. The pressure of the gas at the higher temperatures was calculated 
by the ideal gas approximation. 
formation and non-ideality of the gases that this approximation would not be 
good enough. 
read the cell pressure directly. 
It was feared that because of possible polymer 
A check on these measurements was made by method devised to 
6 
A pressure transducer was mounted 
-4- 
in the cell body and calibrated in the desired pressure range. 
transducer used was a type M6S, Model No. SA-SA manufactured by the Cornyel 
Corporation. 
The pressure 
It is temperature-compensated from 23OC to 15OoC for the range 
of pressure from 0 - 6 atm. It was read when the cell was at the proper 
temperature and its reading checked against the ideal gas approximation. 
The readings differed at most by 5 cm Hg at the highest pressure readings. 
This difference led to a possible error in the line shift measurement of 
about fifteen percent of the average shift observed. 
RESULTS 
Five sets of data were recorded for the line shifts in the first over- 
tone of DF broadened by HF. The temperatures, cells and path lengths are 
given in Table 11. The line shift per unit pressure is presented in Table 
\ I11 for each line measured, The measured line shifts are plotted in Fig- 
ures 2 and 3 as a function of the difference in pressure of the sample and 
reference. It appears that with the exception of a few points there is good 
evidence for the linearity of the shifts with pressure. It is also signifi- 
. .  
cant that the straight lines which have been drawn as the lines of best fit 
pass reasonably well through the origin. This result would indicate that 
no large systematic error in pressure measurements exists. 
The measured shifts as a function of J-number are displayed in Fig. 4. 
The points plotted are the averages of the five sets of data taken. The 
results of Jaffe, et al. for the DC1-HC1 system are also reproduced for 
comparison. 
can be seen from the graph that large amplitude oscillations occur in the 
The average deviations are indicated by the error bars. It 
R-branch and from P ( 3 )  outward in the P-branch. These oscillations are in 
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phase wi th  those i n  the  DC1-HC1 system bu t  are considerably l a r g e r  i n  amp- 
l i t u d e .  I n , t h e  wings, e.g., f o r  t h e  R(6) l i n e  t h e  va lue  of. t h e  s h i f t  i s  
comparable t o  t h e  va lue  found f o r  HF s h i f t e d  by Xenon.7 
5.6 IZ 
This va lue  of 
cm-l /cm Hg i s  indica ted  a t  R(6) on t h e  graph. 
ERRORS 
The e r r o r  ba r s  i n  Fig. 4 represent  t h e  averaging of t h e  s c a t t e r e d  poin ts .  
It is  i l lumina t ing  t o  consider t h e  sources of e r r o r  i n  the  experiment t o  see 
how t h e  estimated e r r o r  compares with measured e r ro r .  
e r r o r  are i n  t h e  pressure  measurement, i n  instrumental  d r i f t  and i n  de te r -  
mination of l i n e  peak. 
The major sources of 
Instrumental  d r i f t  w a s  checked by running and rerunning a l i n e .  For 
example, f o r  t h e  R(1) l i n e  the  magnitude of t h e  maximum frequency d i f f e rence  
i n  t h r e e  runs w a s  0.002 cm which is about 0.4 of t h e  minimum s h i f t  observed. -1 
The problems assoc ia ted  with t h e  measurement of l i n e  cen te r s  and gas im-  
p u r i t y  are r e l a t ed ,  Even a f t e r  a l l  t h e  poss ib le  precautions were taken i n  
the  handling of t h e  DF, a considerable amount of DF, perhaps about 50 per- 
cent of it, w a s  converted i n t o  HF. 
problem. 
This conversion c rea ted  a two-fold 
F i r s t ,  i t  was  no t  poss ib l e  t o  know t h e  exac t  pressure  of DF i n s i d e  
t h e  cell ,  and second i t  required a considerably l a r g e r  amount of gas  i n s i d e  
t h e  r e fe rence  cell .  I f  t h e  gas were pure, a trace of DF would be s u f f i c i e n t  
t o  produce a sharp ly  peaked line--at least near t h e  band center .  However, 
i t  w a s  found t h a t  t h e  converted HF had a s t rong  e f f e c t  upon t h e  peak he ights ,  
tending sharp ly  t o  reduce t h e  l i n e  peak. It w a s  t h i s  e f f e c t  t h a t  prevented 
us from studying t h e  l i n e s  beyond P ( 7 )  and R ( 6 )  and, moreover, l e d  t o  a 
l a r g e r  amount of DF being requi red  t o  obta in  measurable i n t e n s i t i e s  of t h e  
l i n e s  near t h e  band center.  A t  t h e  low pressures  of DF a l i n e  i n  t h e  wing 
is very weakly absorbing. Amplification of t h e  s i g n a l  only increased t h e  
-6- 
noise level, making it difficult to find the line peak precisely. The 
same line at a high pressure of DF is quite flat. The conversion of 
DF to HF also prevented us from reporting on the line shifts of HF per- 
trubed by DF. First, because it was not possible to take a trace of HF 
and large amounts of DF, and second, because flattening of line peaks 
also occurred. 
scatters in the points are found for the lines further away from the band 
center. Those lines were weakly absorbing and hence the peaks were not 
sharply defined. 
was rather natural. 
drift and pressure measurements is about - + .9 cm-l/crn Hg x 
scatter found is - i- .7 cm-'/cm Hg x 10' . 
of scatter was considerably less than the shift observed. 
Along this line it is interesting to note that the most 
In these cases a larger error in determining line peak 
The mean error estimated by adding the errors due to 
The mean 
4 In all the cases the magnitude 
A qualitative approach 
molecular system is given by 
action. Jaffe, et a1.l have 
CONCLUSIONS 
to the origin of the line shifting in this 
the thoery of the near-resonant dipolar inter- 
given the expression for the energy change due 
t o  the dipolar interaction as derived from second order perturbation theory. 
When the molecular parameters for HF and DF are substituted into this ex- 
pression, the calculated energy shifts are such as to lead to large oscil- 
lating line shifts. However, just as in the DCl-HCl case, the predicted 
shifts are exactly opposite to those observed. The shifts not only oscil- 
late but increase in magnitude toward the red in the R-branch and the 
blue in the P-branch. 
-7- 
1. The work was supported by the National Aeronautical ahd Space Admin- 
istration, Grant NGL-43-001-006. 
J.H. Jaffe, M.A. Hirshfeld and A .  Ben-Reuven, J. Chem. Phys., L 40
1705 (1964). 
2. 
3. Private communication to the authors from Arieh Rosenberg, Institute of 
Chemistry, Tel-Aviv University, 
4. Herndon, J.A., W.E. Deeds, N.M. Gailar, W.F. Herget, R.J. Lovell and 
A.H. N€elsen, J. Optical Society, - 52, 1108 (1962). 
5 .  Herndon, J.A., W.E. Deeds, N.M. Gailar, W.F. Herget, R.J; Lovell and 
A.H. Nielsen, J. Optical Society, - 52, 113 (1962). 
This direct-reading method was not available until near the end of this 6 .  
study. The measurements could not be more extensively redone because of 
time committments.for the spectrometer. 
7. J.H. Jaffe, A. RosBnberg, M.A. Hirshfeld, and N.M. Gailar, J. Chem. Phys., 
- 43, 1525 (1965). 
Table I 
bbserved line shifts per unit pressure in HF 
Line 
. .  
Line Shift per 
Unit Pressure* 
+ 3.9 
+ . 91  
f .53 - 3.24 - 3 .44  - 3.99 - 3.54 - 2.66 - 2.86 
+ 1.79  
+ . 91  - .66 
- .36 
+ 1.47 
f 1.15 
*Averages of measurements at pressures of 
37.5 cm Hg, 76 cm Hg, 'and 113.5 cm Hg 
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Figure Captions 
1. Figure 1. 
0 - Herget e t  a l ,  0 - Desai e t  a l ,  - rev ised  curve using 
t h e  r e s u l t s  of both s tud ie s .  
Line S h i f t s  per u n i t  p ressure  i n  t h e  1-0 band of HF. 
2. Figure 2. Measured Line s h i f t s  f o r  t h e  R-branch l i n e s .  
3. Figure 3.  Measured l i n e  s h i f t s  f o r  t he  P-branch l i n e s .  
4. Figure 4. A comparison of t h e  pressure-induced s h i f t s  of l i n e s  
i n  t h e  2-0 bands of DF-HF and DC1-HC1. ----- DF-HF, - DC 1-HC 1, 
_---- t hese  l i n e s  as they appear i n  J a f f e  e t  a1.l 
d i c a t e s  t he  va lue  measured by J a f f e  e t  a14 f o r  t h e  s h i f t  of R(6) 
i n  t h e  2-0 band of HF-Xe. . 
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Line shifts in the first overtone of DF broadened by HF

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