Research Article | Open Access
K. S. Ojha, R. Gopal, "Laser Induced Spectra of SiN Molecule in Near IR Region", International Journal of Spectroscopy, vol. 2013, Article ID 915365, 5 pages, 2013. https://doi.org/10.1155/2013/915365
Laser Induced Spectra of SiN Molecule in Near IR Region
Laser-induced spectra of SiN molecule are recorded in the region of 670–1060 nm using laser-induced spectroscopy technique and about 80 bands are observed. Out of total 80 bands, 49 bands are attributed to F-B system and the rest 27 bands are analyzed into J-D system. The rest 18 bands are unidentified. The molecular constant of the , , and states is determined and reported.
Thirty-five red degraded emission bands of SiN molecule, lying in the region of 380–495 nm, were first observed by Jevons . Mulliken  reinvestigated the spectra in 380–530 nm region and observed 53 red degraded bands including the bands reported by Jevons  and attributed these bands to B2Σ+-X2Σ+ system of SiN molecule. In addition to B2Σ+-X2Σ+ transition, a new transition C-A2Π was also observed by Mulliken  in near Uv-green region. Jenkins and De Laszlo , on the basis of rotational analysis of B2Σ+-X2Σ+ transition, concluded that the level of B2Σ+ is perturbed. Schoffield and Broida  investigated the chemiluminescence spectra of SiN molecule and observed two new electronic transitions in 518–602 and 554–725 nm regions along with B2Σ+-X2Σ+, and C-A2Π systems. Bredohl et al.  reinvestigated the spectra in 310–560 nm region and observed three new electronic transitions D2Π-A2Π, L2Π-A2Π, and K2Π-A2Π along with B2Σ+-X2Σ+ system.
Foster , on the basis of rotational study of four bands, renamed K2Π-A2Π system reported by Bredohl et al.  as B2Σ+-A2 system of SiN molecule and calculated cm−1 for A2 state. Foster et al.  rotationally analyzed (2,0) band of the A2-X2Σ+ system along with B2Σ+-X2Σ+, D2Π-A2Π, and L2Π-A2Π systems and improved the molecular constants of A2 and X2Σ+ states. Cai et al.  calculated rotational and vibrational constants for X2Σ+and A2Π states of the SiN molecule using complete active space SCF (CASSCF), multireference CI (MRCI), and coupled cluster (CCSD(T)) levels. The potential energy curves of the SiN molecule for the low-lying electronic states were also computed by Cai et al.  using internally contracted multireference configuration interaction (CMRCI) level.
Laser-induced spectroscopy technique is being widely used in the field of molecular spectroscopy to provide laboratory data of molecules. Fu et al. , Bondybey , Hopkins et al. , and Ojha and Gopal [13, 14] have observed a number of new band systems of different molecules using this technique. Therefore, it was decided to investigate the emission spectra of SiN molecule in near IR region. In the present work, the emission spectra of SiN molecule were investigated in 670–1060 nm region to provide the laboratory data.
2. Experimental Technique
The experimental setup comprised of a Pulsed Nd: YAG laser (Spectra Physics, USA, repetition rate 10 Hz), a laser ablation chamber ( diameter) mounted on the throat of rotary and diffusion pumps, and a computer-controlled Spex TRIAX 320 M monochromator (Jobin Yovn, USA) fitted with TE cooled ICCD detector (Jobin Yovn, USA) system having spectral resolution of 0.06 nm for 1200 grs/mm grating. The silicon nitride rod (purity 99.999%, Goodfellow, UK) was clamped inside the chamber. The ablation chamber was evacuated up to 10−3 torr using rotary pump. The chamber was flashed two-three times with high purity Argon gas (purity 99.99%) to remove the contaminants. The chamber was then filled with the same argon gas up to a pressure of 0.1 mbar. The silicon nitride plasma was produced by focusing 355 nm of Pulsed Nd: YAG laser (70 mJ) on continuously rotating and translating silicon nitride rod with the help of a convex lens of focal length 50 cm. The produced plasma was allowed to cool adiabatically from 80 to 500 ns delay time and the cooled plasma was focused on the entrance slit of computer-controlled monochromator using a cylindrical lens of focal length 25 cm. The TE cooled ICCD detector with gating speed of 5 ns was synchronized with Nd: YAG laser in Q-switch mode. For spectroscopic investigation, signals were sent to computer and data acquisition was made using Spectra Max software. The Grams 32 software was used for peak picking and peak marking. The spectra of SiN molecule were observed at 120 ns delay time using 600 groves/mm grating blazed at 750 nm in this region.
3. Analysis and Results
The spectra of SiN molecule are investigated in the region of 670–1060 nm using laser-induced spectroscopy technique. Total of 80 bands are observed in this region. Out of total 80 bands, 62 bands are analyzed into two new doublet-doublet electronic transition F2Π-B2Σ+ and J2Π-D2Σ− reported by Cai et al.  of SiN molecule. The rest 18 bands are unanalyzed. The details of the analyses of these systems are given below.
3.1. New F2Π-B2Σ+ System
The F2Π-B2Σ+ system lies in the region of 680–1060 nm. Total 49 red degraded and single headed bands of this system are identified with at 974.60 nm. The observed 49 bands are assigned to , 1, 2, 3, 4, 5, 6, 7, and 8 sequences. The bands of sequence are not observed due to the ICCD response. The bands of sequence are observed with very low to signal noise ratio, while the bands of the rest of sequences are well developed and observed with good intensity. The value of calculated in this experiment for F2Π state is found to be 34908.76 cm−1 which is close to that theoretically calculated by Cai et al. . The experimentally calculated molecular constant of F2Π and B2Σ− states is very close to that reported by Cai et al.  and presented in Table 3. Figures 1, 2, 3, and 4 represents the spectra of F2Π-B2Σ+ system and the bandhead data are given in Table 1.
3.2. New J2Π-D2Σ− System
The system lies in the region of 715–1045 nm with (0, 0) at 897.42 nm. The total 27 violet degraded and single headed bands of the J2Π-D2Σ− system are identified and attributed to , ±1, ±2 and ±3 sequences. All the bands of the system are well developed and observed with good intensity. The value of calculated experimentally is found to 44871.20 cm−1 which is very close to 44861.00 reported by Cai et al. . The experimentally calculated values of molecular constants for J2Π and D2Σ− states is very close to those reported by Cai et al. , and presented in Table 3. The spectra of the system are shown in Figures 1, 2, 3, and 4. The bandhead data of this system are given in Table 2.
|Reported by , †calculated in the present work.|
The molecular constants calculated experimentally for B2Σ−, D2Σ−, F2Π, and J2Π states are very close to those reported by Cai et al. . The close matching of molecular constants of this state along with the values of F2Π and J2Π sates confirmed that the spectra are due to SiN molecule.
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