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Fourier-transformed infrared photoacoustic spectroscopy of polystyrene film
CIll~Xt1CALI’IIYSICS LE’l”rE1IS
V&tne 68, number 2.3
FOURIER-TRANSFORMED OF POLYSTYRENE
INFRARED
red
the
(FT IR)
technique photoacoustic
01’
SPECTROSCOPY
Plthf
it is the IHI~~IOSSof this brief comnlunicafion ititroducc
PHOTOACOUSTIC
15 Dccembcr I979
~o’ourier-tr;;rtst’orl!letl spectroscopy
solids. In this paper, a spectrum of a
as
to iIlfril-
applied
to
polystyrene is described, by way of illustration. It is shown that photoacoustic spectroscopy (PAS) can be used in the 4000-800 cm-l spectral range with resolution of 8 cm-l and !imited ultimately by the instrlmlental parameters of the FT IR spectrometer. An FT iR spectrometer has the great advanrage that the spectral throughput is up to 50 times higher than the throughput of a dispersive instrumen:. This is Jacquinot’s advantage. The multiplexing or Fellgett’s advantage further complements the technique since it means that the eventual resoktion of the PAS spectrum is tzot limited by signal strength at the detector. These advantages have been utilized here to measure the infrared PAS spectrum of poly(styrene) with 8 cm-l resolution in the 4000-SO0 cm-1 spectral range. The spectrum shown in fig. 1 is the FT IR PAS spectrum of polystyrene. It does not at firs: glance‘ resemble the conventional IR absorption spectrum of polystyrene because this spectrum represents the total absorbed power at each frequency. It is also a singlebeam spectrum and so has not at this stage been corrected for decreased optical transmission of the spectrometer from 1200-600 cm-1 and for attenuation at the Iow frequencies introduced by the detection electronics. Nevertheless, several features are clearly film
of
Fig. 1. 8 cm-’ resolution single-beam FT IR photoacoustic absorption spectrum of a polystyrene film_~2048 interferometer scans were condded to produce this specrrum. This is an uncorrected spectrum showin_r amplifier distorrion and wriation in PAS signal strength with the moduIation frequency. Correction procedures wili be detailed in a forthcoming paper.
identifiable_ The aromatic and aliphatic C-H stretching at 2800-3100 cm-l is easily visible as is the 1503 cm-l spike so often used to calibrate dispersion instruments_ Each of the peaks in the 2000-l 300 cm-1 range can be assigned to either absorption by polystyrene or to absorption by residual water vapor in the sample chamber_ The intense signal centered at 2349 cm-l is due to absorption by ambient air concentrations of CO, in the sample chamber. Absorption due to CO, and.HZO points to the sensitivity of 45.5
Volume 68. number 23
15 December 1979
ff IEJIICXL PHYSICS LETTERS
the technique for studying the nonradiative dec3y charmed for pses which are vibrationally excited_ The negative going spikes et multiples of 340 cm-t are due to ground loops in the detection system_ The photoacoustic cell and preamplifier combination was the same one de&bed elsewhere (I] except that a PZKI entrzmce window was used_ The sample and cell were pIaced at the focus of a 4 X beam twndenser in the nmple chamber of a Dig&b FfS-20 FT IR spectrometer_ The output of the I/2 CR eledret microphone-Ithaca f43L preampiifier was passed through a high-pass filter (3dB point = 30 IIz), a X 10 audioamplifier and connected directIy to the mid-IR amplirier section of the Ff IR spectrometer_ Full details wiii be given in a subsequent publication. This demoztration opens up the infrared range to the potential of Ff techniques for gathering information on surfaces, in particular, rough surfaces which iire not good candidates for conventional IR-reflectance techniques_ Thus such samples as catalysts, gases, plant surfaces, skins. paints, cosmetics, etc_ can now be examined in the IR region with resolutions up to 0.1 cm-t for most current commercial FT IR spectrometers- In addition to straight spectraI information
in the infixed, tile technique may also prove useful for examining fluorescence and energy-transfer quaturn yields for gases and solids used in chemical and solid-state lasers by techniques which have been demonstrated in the W-visible spectral region [ 1,z] _ WhiIe the FT IR technique has been applied to the study of gases in a spectrophone [3] and Fouriertransform techniques have been applied to surfaces in the visible [4],
this study demonstrates
for
the study of solids in the infrared zpectnl range. The author gratefuIIy xknowiedges helpful suses[ions from Professor J_ Paul Devlin. the donors of the Petroleum Research Fund, administered by the ACS, and the Nationrd Science Foundation.
References [ 11 MC_ Rockley and K.BL \Vau$. Chem. PII~s_ Letters 54
(I 978) 597_ {2) BLG. Rockley. Chem. Phys. Letters JO (1977) 417. [3] G_ Busse and B_ Buitemer, Infrared Phys. 1s (1978) 255. [4] 3LM_ l%rrow. R-K Burxdlamand EX_ Eyring, Xppl Phyr Letters 33 (1978) 735.
456
the use of
FT IR techniques combined with photoacoustics
V&tne 68, number 2.3
FOURIER-TRANSFORMED OF POLYSTYRENE
INFRARED
red
the
(FT IR)
technique photoacoustic
01’
SPECTROSCOPY
Plthf
it is the IHI~~IOSSof this brief comnlunicafion ititroducc
PHOTOACOUSTIC
15 Dccembcr I979
~o’ourier-tr;;rtst’orl!letl spectroscopy
solids. In this paper, a spectrum of a
as
to iIlfril-
applied
to
polystyrene is described, by way of illustration. It is shown that photoacoustic spectroscopy (PAS) can be used in the 4000-800 cm-l spectral range with resolution of 8 cm-l and !imited ultimately by the instrlmlental parameters of the FT IR spectrometer. An FT iR spectrometer has the great advanrage that the spectral throughput is up to 50 times higher than the throughput of a dispersive instrumen:. This is Jacquinot’s advantage. The multiplexing or Fellgett’s advantage further complements the technique since it means that the eventual resoktion of the PAS spectrum is tzot limited by signal strength at the detector. These advantages have been utilized here to measure the infrared PAS spectrum of poly(styrene) with 8 cm-l resolution in the 4000-SO0 cm-1 spectral range. The spectrum shown in fig. 1 is the FT IR PAS spectrum of polystyrene. It does not at firs: glance‘ resemble the conventional IR absorption spectrum of polystyrene because this spectrum represents the total absorbed power at each frequency. It is also a singlebeam spectrum and so has not at this stage been corrected for decreased optical transmission of the spectrometer from 1200-600 cm-1 and for attenuation at the Iow frequencies introduced by the detection electronics. Nevertheless, several features are clearly film
of
Fig. 1. 8 cm-’ resolution single-beam FT IR photoacoustic absorption spectrum of a polystyrene film_~2048 interferometer scans were condded to produce this specrrum. This is an uncorrected spectrum showin_r amplifier distorrion and wriation in PAS signal strength with the moduIation frequency. Correction procedures wili be detailed in a forthcoming paper.
identifiable_ The aromatic and aliphatic C-H stretching at 2800-3100 cm-l is easily visible as is the 1503 cm-l spike so often used to calibrate dispersion instruments_ Each of the peaks in the 2000-l 300 cm-1 range can be assigned to either absorption by polystyrene or to absorption by residual water vapor in the sample chamber_ The intense signal centered at 2349 cm-l is due to absorption by ambient air concentrations of CO, in the sample chamber. Absorption due to CO, and.HZO points to the sensitivity of 45.5
Volume 68. number 23
15 December 1979
ff IEJIICXL PHYSICS LETTERS
the technique for studying the nonradiative dec3y charmed for pses which are vibrationally excited_ The negative going spikes et multiples of 340 cm-t are due to ground loops in the detection system_ The photoacoustic cell and preamplifier combination was the same one de&bed elsewhere (I] except that a PZKI entrzmce window was used_ The sample and cell were pIaced at the focus of a 4 X beam twndenser in the nmple chamber of a Dig&b FfS-20 FT IR spectrometer_ The output of the I/2 CR eledret microphone-Ithaca f43L preampiifier was passed through a high-pass filter (3dB point = 30 IIz), a X 10 audioamplifier and connected directIy to the mid-IR amplirier section of the Ff IR spectrometer_ Full details wiii be given in a subsequent publication. This demoztration opens up the infrared range to the potential of Ff techniques for gathering information on surfaces, in particular, rough surfaces which iire not good candidates for conventional IR-reflectance techniques_ Thus such samples as catalysts, gases, plant surfaces, skins. paints, cosmetics, etc_ can now be examined in the IR region with resolutions up to 0.1 cm-t for most current commercial FT IR spectrometers- In addition to straight spectraI information
in the infixed, tile technique may also prove useful for examining fluorescence and energy-transfer quaturn yields for gases and solids used in chemical and solid-state lasers by techniques which have been demonstrated in the W-visible spectral region [ 1,z] _ WhiIe the FT IR technique has been applied to the study of gases in a spectrophone [3] and Fouriertransform techniques have been applied to surfaces in the visible [4],
this study demonstrates
for
the study of solids in the infrared zpectnl range. The author gratefuIIy xknowiedges helpful suses[ions from Professor J_ Paul Devlin. the donors of the Petroleum Research Fund, administered by the ACS, and the Nationrd Science Foundation.
References [ 11 MC_ Rockley and K.BL \Vau$. Chem. PII~s_ Letters 54
(I 978) 597_ {2) BLG. Rockley. Chem. Phys. Letters JO (1977) 417. [3] G_ Busse and B_ Buitemer, Infrared Phys. 1s (1978) 255. [4] 3LM_ l%rrow. R-K Burxdlamand EX_ Eyring, Xppl Phyr Letters 33 (1978) 735.
456
the use of
FT IR techniques combined with photoacoustics