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A molecular iodine atlas in ascii format
Journal of Molecular Spectroscopy 233 (2005) 157–159 www.elsevier.com/locate/jms
Note
A molecular iodine atlas in ascii format Houssam Salami, Amanda J. Ross * Laboratoire de Spectrome´trie Ionique et Mole´culaire, Universite´ Lyon I et CNRS (UMR 5579), Baˆtiment A. Kastler, Domaine Scientifique de la Doua, 69622 Villeurbanne Cedex, France Received 22 April 2005
The B–X transition in the iodine molecule has provided a convenient frequency calibration for many spectroscopic experiments in the visible and near-infrared for many years, following the publication of the iodine atlas (Part I) by Gerstenkorn and Luc [1]. Their extensive Fourier transform measurements continued towards the infrared, supplying a valuable reference spectrum that covers the B–X transition in I2 over the 11 000– 20 000 cm 1 region [1–3]. However, the spectrum recorded at Laboratoire Aime´ Cotton is available only in paper format and requires a small correction ( 0.0056 cm 1) to be applied above 14 000 cm 1 [4]. (This correction in fact depends slightly on frequency, as the authors pointed out in the introduction to the third part of their atlas [3]). Weak transitions and heavily distorted lines do not feature in the associated peak-list, and this can be inconvenient when trying to calibrate a relatively short stretch of spectrum. The strongest part of the I2 B–X spectrum (15 000– 19 000 cm 1) has since been recorded at sub-Doppler resolution by Katoˆ et al. [5]. This atlas provides a far superior set of wavelength references, but has the drawback of being slow to use, in view of the time required to convert etalon fringe readings into cm 1 units. A more elaborate set-up is also required to record the subDoppler iodine spectrum as a reference in the first place. Another possibility is to calculate the reference absorption spectrum at any chosen resolution, as offered for example by the commercial package Iodine Spec [6]. Since in many practical applications, the Dopplerlimited iodine spectrum is employed for calibration purposes, we propose here an experimental absorption spectrum of iodine, in a single ascii file, covering the *
Corresponding author. Fax: +33 472447851. E-mail address: [email protected] (A.J. Ross).
0022-2852/$ - see front matter 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jms.2005.06.002
range 14 250–20 000 cm 1. We have found it very convenient to calibrate excitation spectra by matching recorded iodine fluorescence signals to this reference absorption spectrum using graphics routines. Given the lineshapes recorded in the Doppler-limited iodine absorption spectrum, illustrated for example in Fig. 1, peak-finding routines can easily return measured wavenumbers differing by ±0.005 cm 1: matching to known lineshapes is more satisfactory. The transmission spectrum (in ascii format) is presented as supplementary material, deposited with the data archive of this journal. The iodine absorption spectrum has been recorded on a continuous scan (Bomem DA3) FT interferometer, from 14 250 to 20 100 cm 1, at an instrumental resolution of 0.02 cm 1. Measured linewidths, due to unresolved hyperfine structure, are typically 0.035– 0.05 cm 1. The source was an iodine cell 50 cm in length with a 6 cm sidearm, illuminated by a 100 W halogen lamp, and the detector was a Si–avalanche diode (RCA). The temperature of the main body of the cell was increased from 20 C (short wavelength end of the spectrum) up to 190 C (below 16 400 cm 1) to enhance absorption without causing saturation of the stronger features in the system. Spectra were taken at room temperature from 16 500 to 20 100 cm 1, at 50 C for the region 15 400–17 400 cm 1, and at 190 C for the weaker bands (14 250–16 500 cm 1). Since both the intensity of the halogen lamp and the detector sensitivity fall off at short wavelengths, the spectrum was recorded in four pieces, to optimise the signal/noise ratio. Optical filters were used to select a given wavelength range (details are given in Table 1), and gain settings were then optimised to suit the level of signal detected. The same optical alignment was maintained for all four spectra. The recording time was typically 8 h for each portion of the spectrum. The spectra were then spliced together,
158
H. Salami, A.J. Ross / Journal of Molecular Spectroscopy 233 (2005) 157–159
Fig. 1. Part of the transmission spectrum of molecular iodine.
Table 1 Optional filters and temperature settings used in this work Wavenumber range (cm 1)
Optical filters
Temperature (C)
19 100–20 500 16 500–19 500 15 400–17 400 14 500–16 500
Corning Corning Corning Corning
20 20 50 190
CS CS CS CS
4-97 + Corning CS 5-56 4-97 3-67 + Corion LS 650 2-61 + Corion LS 700
averaging the transmission signals (GRAMS software, from Galactic Inc.). The frequency calibration was then established from some two hundred lines, comparing measured line centres against measurements taken from the Doppler Free High Resolution Spectral Atlas of the Iodine Molecule, published by Katoˆ et al. [5], and from
the Doppler-limited absorption spectrum of Gerstenkorn and Luc [1,2] (taking into account their recommended correction). A frequency-dependent correction (4 · 10 7 r) was applied to bring our work into line with these more reliable sources. A portion of the final spectrum is illustrated in Fig. 1. Fig. 2 displays a selection of differences between wavenumbers taken from our ÔcorrectedÕ spectrum and those measured: (a) from the Doppler-limited trace in the Katoˆ atlas, indicated with crosses and (b) peaks listed in the atlases published by Gerstenkorn and co-workers, indicated with filled circles. We estimate that our spectrum should be reliable to ±0.003 cm 1, except for the region 15797.7– 15798.5 cm 1, where the spike at 15 798 cm 1 corresponds to the HeNe laser, used for internal calibration of the Fourier spectrometer.
Fig. 2. Scattergram of residuals, comparing measurements taken from our spectrum with those taken from the Atlases of Gerstenkorn, Luc, and co-workers (filled circles) and from the sub-Doppler atlas of Katoˆ et al. (crosses).
H. Salami, A.J. Ross / Journal of Molecular Spectroscopy 233 (2005) 157–159
Appendix A. Supplementary data Supplementary data for this article (the transmission spectrum in ascii format) are available on ScienceDirect (www.sciencedirect.com) and as part of the Ohio State University Molecular Spectroscopy Archives (http:// msa.lib.ohio-state.edu/jmsa_hp.htm). References [1] S. Gerstenkorn, P. Luc, Atlas du spectre dÕabsorption de la mole´cule dÕiode (15 600–20 000 cm 1), Editions CNRS, Paris, 1977.
159
[2] S. Gerstenkorn, P. Luc, Atlas du spectre dÕabsorption de la mole´cule dÕiode (14 000–15 600 cm 1), Laboratoire Aime´ Cotton, CNRS II, Orsay, 1980. [3] S. Gerstenkorn, J. Verge`s, J. Chevillard, Atlas du spectre dÕabsorption de la mole´cule dÕiode 11 000–14 000 cm 1, Laboratoire Aime´ Cotton, CNRS II, Orsay, 1982. [4] S. Gerstenkorn, P. Luc, Revue de Physique Applique´e 14 (1979) 791–794. [5] H. Katoˆ et al., Doppler Free High Resolution Spectral Atlas of Iodine Molecule, Japan Society for the Promotion of Science (2000). [6] Iodine Spectrum Calculating Software ‘‘Iodine Spec,’’ from Toptica Photonics, Germany.
Note
A molecular iodine atlas in ascii format Houssam Salami, Amanda J. Ross * Laboratoire de Spectrome´trie Ionique et Mole´culaire, Universite´ Lyon I et CNRS (UMR 5579), Baˆtiment A. Kastler, Domaine Scientifique de la Doua, 69622 Villeurbanne Cedex, France Received 22 April 2005
The B–X transition in the iodine molecule has provided a convenient frequency calibration for many spectroscopic experiments in the visible and near-infrared for many years, following the publication of the iodine atlas (Part I) by Gerstenkorn and Luc [1]. Their extensive Fourier transform measurements continued towards the infrared, supplying a valuable reference spectrum that covers the B–X transition in I2 over the 11 000– 20 000 cm 1 region [1–3]. However, the spectrum recorded at Laboratoire Aime´ Cotton is available only in paper format and requires a small correction ( 0.0056 cm 1) to be applied above 14 000 cm 1 [4]. (This correction in fact depends slightly on frequency, as the authors pointed out in the introduction to the third part of their atlas [3]). Weak transitions and heavily distorted lines do not feature in the associated peak-list, and this can be inconvenient when trying to calibrate a relatively short stretch of spectrum. The strongest part of the I2 B–X spectrum (15 000– 19 000 cm 1) has since been recorded at sub-Doppler resolution by Katoˆ et al. [5]. This atlas provides a far superior set of wavelength references, but has the drawback of being slow to use, in view of the time required to convert etalon fringe readings into cm 1 units. A more elaborate set-up is also required to record the subDoppler iodine spectrum as a reference in the first place. Another possibility is to calculate the reference absorption spectrum at any chosen resolution, as offered for example by the commercial package Iodine Spec [6]. Since in many practical applications, the Dopplerlimited iodine spectrum is employed for calibration purposes, we propose here an experimental absorption spectrum of iodine, in a single ascii file, covering the *
Corresponding author. Fax: +33 472447851. E-mail address: [email protected] (A.J. Ross).
0022-2852/$ - see front matter 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jms.2005.06.002
range 14 250–20 000 cm 1. We have found it very convenient to calibrate excitation spectra by matching recorded iodine fluorescence signals to this reference absorption spectrum using graphics routines. Given the lineshapes recorded in the Doppler-limited iodine absorption spectrum, illustrated for example in Fig. 1, peak-finding routines can easily return measured wavenumbers differing by ±0.005 cm 1: matching to known lineshapes is more satisfactory. The transmission spectrum (in ascii format) is presented as supplementary material, deposited with the data archive of this journal. The iodine absorption spectrum has been recorded on a continuous scan (Bomem DA3) FT interferometer, from 14 250 to 20 100 cm 1, at an instrumental resolution of 0.02 cm 1. Measured linewidths, due to unresolved hyperfine structure, are typically 0.035– 0.05 cm 1. The source was an iodine cell 50 cm in length with a 6 cm sidearm, illuminated by a 100 W halogen lamp, and the detector was a Si–avalanche diode (RCA). The temperature of the main body of the cell was increased from 20 C (short wavelength end of the spectrum) up to 190 C (below 16 400 cm 1) to enhance absorption without causing saturation of the stronger features in the system. Spectra were taken at room temperature from 16 500 to 20 100 cm 1, at 50 C for the region 15 400–17 400 cm 1, and at 190 C for the weaker bands (14 250–16 500 cm 1). Since both the intensity of the halogen lamp and the detector sensitivity fall off at short wavelengths, the spectrum was recorded in four pieces, to optimise the signal/noise ratio. Optical filters were used to select a given wavelength range (details are given in Table 1), and gain settings were then optimised to suit the level of signal detected. The same optical alignment was maintained for all four spectra. The recording time was typically 8 h for each portion of the spectrum. The spectra were then spliced together,
158
H. Salami, A.J. Ross / Journal of Molecular Spectroscopy 233 (2005) 157–159
Fig. 1. Part of the transmission spectrum of molecular iodine.
Table 1 Optional filters and temperature settings used in this work Wavenumber range (cm 1)
Optical filters
Temperature (C)
19 100–20 500 16 500–19 500 15 400–17 400 14 500–16 500
Corning Corning Corning Corning
20 20 50 190
CS CS CS CS
4-97 + Corning CS 5-56 4-97 3-67 + Corion LS 650 2-61 + Corion LS 700
averaging the transmission signals (GRAMS software, from Galactic Inc.). The frequency calibration was then established from some two hundred lines, comparing measured line centres against measurements taken from the Doppler Free High Resolution Spectral Atlas of the Iodine Molecule, published by Katoˆ et al. [5], and from
the Doppler-limited absorption spectrum of Gerstenkorn and Luc [1,2] (taking into account their recommended correction). A frequency-dependent correction (4 · 10 7 r) was applied to bring our work into line with these more reliable sources. A portion of the final spectrum is illustrated in Fig. 1. Fig. 2 displays a selection of differences between wavenumbers taken from our ÔcorrectedÕ spectrum and those measured: (a) from the Doppler-limited trace in the Katoˆ atlas, indicated with crosses and (b) peaks listed in the atlases published by Gerstenkorn and co-workers, indicated with filled circles. We estimate that our spectrum should be reliable to ±0.003 cm 1, except for the region 15797.7– 15798.5 cm 1, where the spike at 15 798 cm 1 corresponds to the HeNe laser, used for internal calibration of the Fourier spectrometer.
Fig. 2. Scattergram of residuals, comparing measurements taken from our spectrum with those taken from the Atlases of Gerstenkorn, Luc, and co-workers (filled circles) and from the sub-Doppler atlas of Katoˆ et al. (crosses).
H. Salami, A.J. Ross / Journal of Molecular Spectroscopy 233 (2005) 157–159
Appendix A. Supplementary data Supplementary data for this article (the transmission spectrum in ascii format) are available on ScienceDirect (www.sciencedirect.com) and as part of the Ohio State University Molecular Spectroscopy Archives (http:// msa.lib.ohio-state.edu/jmsa_hp.htm). References [1] S. Gerstenkorn, P. Luc, Atlas du spectre dÕabsorption de la mole´cule dÕiode (15 600–20 000 cm 1), Editions CNRS, Paris, 1977.
159
[2] S. Gerstenkorn, P. Luc, Atlas du spectre dÕabsorption de la mole´cule dÕiode (14 000–15 600 cm 1), Laboratoire Aime´ Cotton, CNRS II, Orsay, 1980. [3] S. Gerstenkorn, J. Verge`s, J. Chevillard, Atlas du spectre dÕabsorption de la mole´cule dÕiode 11 000–14 000 cm 1, Laboratoire Aime´ Cotton, CNRS II, Orsay, 1982. [4] S. Gerstenkorn, P. Luc, Revue de Physique Applique´e 14 (1979) 791–794. [5] H. Katoˆ et al., Doppler Free High Resolution Spectral Atlas of Iodine Molecule, Japan Society for the Promotion of Science (2000). [6] Iodine Spectrum Calculating Software ‘‘Iodine Spec,’’ from Toptica Photonics, Germany.