3:30 PM - 3:45 PM
[MZZ42-06] Wavenumber calibration of naphthalene from next-generation high-resolution Raman spectroscopy and theoretical calculations
Keywords:Raman spectroscopy, high wavenumber resolution, naphthalene, 513 cm−1, 510 cm−1
Naphthalene (molecular formula: C10H8), along with neon lamps, is one of the most commonly used reference materials for wavenumber calibration in Raman spectroscopy. In particular, its representative Raman peaks at wavenumbers 513.8 cm-1 and 763.8 cm-1 have been reported (McCreery research group), making it indispensable for calibration in the low wavenumber region. Thus, naphthalene has been a keystone of Raman spectroscopy for many years, and both experimental and theoretical calculations have suggested the existence of a Raman peak at wavenumber position 510 cm-1 in addition to the 513 cm-1 wavenumber position (e.g. Hanson and Gee, 1969; Shinohara et al.) However, this Raman peak has not been reported by subsequent studies (e.g., Ohta and Ito, 1977; Librando and Alparone, 2007), and it is not clear whether the Raman peak of naphthalene exists at the wavenumber position 510 cm-1, or whether the conventional Raman spectrometer's wavenumber resolution has remained unresolved. Therefore, we have found that in rock-forming minerals such as quartz (SiO2), olivine ((Mg, Fe)2SiO4), and bridgmanite ((Mg, Fe)SiO3), which have major Raman peaks in the low wavenumber range around 500 cm-1, the wavenumber difference of up to 3 cm -1 in such orogenic minerals as (Mg, Fe)2SiO4 and bridgmanite ((Mg, Fe)SiO3).
In this study, we attempted to calibrate the wavenumber of naphthalene with high precision using Raman spectroscopy and theoretical calculations (scaling factor: TPSSh/6-311G). The Raman spectrometer with high wavenumber resolution was installed in the Earth System Chemistry Laboratory of the Materials Science Group of the Solar and Planetary System at Kyushu University. The grating, exposure time, laser power, and laser wavelength were set to 1200 lines/mm, 30 s, 50 mW, and 633 nm, respectively (pixel resolution: 0.16 cm-1). A neon lamp was used for wavenumber calibration. The wavenumber positions of the Raman shift of naphthalene obtained from the measurements were confirmed to be derived from naphthalene from theoretical calculations.
As a result, both the actual measurements and theoretical calculations indicate that naphthalene has a Raman peak at wavenumber position 509 cm-1 in addition to the existing Raman peak at wavenumber position 513 cm-1. Furthermore, the ratio of the intensities of these two Raman peaks at 513 cm-1 and 509 cm-1 may depend on the crystallographic orientation of naphthalene, and if a spectrometer with a wavenumber resolution that cannot separate both peaks is used, an orientation dependence will also appear at the wavenumber position If a spectrometer with a wavenumber resolution that cannot separate both peaks is used, an azimuthal dependence of the wavenumber position will also appear.
The above results suggest that the Raman shift on the low wavenumber side obtained by wavenumber calibration using naphthalene should be reconsidered. Furthermore, the determination of chemical composition of rock-forming minerals using Raman spectrometer (Yasuzuka et al., 2009; Ishibashi et al., 2012) and pressure calibration based on ruby and zircon with Raman peaks on the low wavenumber side (e.g., Mao et al., 1978; Schmidt et al., 2012), which have Raman peaks at low wavenumbers.
In this study, we attempted to calibrate the wavenumber of naphthalene with high precision using Raman spectroscopy and theoretical calculations (scaling factor: TPSSh/6-311G). The Raman spectrometer with high wavenumber resolution was installed in the Earth System Chemistry Laboratory of the Materials Science Group of the Solar and Planetary System at Kyushu University. The grating, exposure time, laser power, and laser wavelength were set to 1200 lines/mm, 30 s, 50 mW, and 633 nm, respectively (pixel resolution: 0.16 cm-1). A neon lamp was used for wavenumber calibration. The wavenumber positions of the Raman shift of naphthalene obtained from the measurements were confirmed to be derived from naphthalene from theoretical calculations.
As a result, both the actual measurements and theoretical calculations indicate that naphthalene has a Raman peak at wavenumber position 509 cm-1 in addition to the existing Raman peak at wavenumber position 513 cm-1. Furthermore, the ratio of the intensities of these two Raman peaks at 513 cm-1 and 509 cm-1 may depend on the crystallographic orientation of naphthalene, and if a spectrometer with a wavenumber resolution that cannot separate both peaks is used, an orientation dependence will also appear at the wavenumber position If a spectrometer with a wavenumber resolution that cannot separate both peaks is used, an azimuthal dependence of the wavenumber position will also appear.
The above results suggest that the Raman shift on the low wavenumber side obtained by wavenumber calibration using naphthalene should be reconsidered. Furthermore, the determination of chemical composition of rock-forming minerals using Raman spectrometer (Yasuzuka et al., 2009; Ishibashi et al., 2012) and pressure calibration based on ruby and zircon with Raman peaks on the low wavenumber side (e.g., Mao et al., 1978; Schmidt et al., 2012), which have Raman peaks at low wavenumbers.