Infrared spectrometer quantum

Actual infrared spectra are complicated by the presence of more complex motions (stretches involving more than two atoms, wagging, etc.), and absorption to higher quantum states (overtones), so infrared spectra can become quite complex. This is not necessarily a disadvantage, however, because such spectra can serve as a fingerprint that is unique to a particular molecule and can be helpful in identifying it. Largely for this reason, infrared spectrometers are standard equipment in most chemistry laboratories. 

In most fields of physical chemistry, the use of digital computers is considered indispensable. Many things are done today that would be impossible without modem computers. These include Hartree-Fock ab initio quantum mechanical calculations, least-squares refinement of x-ray crystal stmctures with hundreds of adjustable parameters and mar r thousands of observational equations, and Monte Carlo calculations of statistical mechanics, to mention only a few. Moreover computers are now commonly used to control commercial instalments such as Fourier transform infrared (FTIR) and nuclear magnetic resonance (FT-NMR) spectrometers, mass spectrometers, and x-ray single-crystal diffractometers, as well as to control specialized devices that are part of an independently designed experimental apparatus. In this role a computer may give all necessary instaic-tions to the apparatus and record and process the experimental data produced, with relatively little human intervention. 

Sutherland predicted an observable (140 kHz) tunneling inversion in the ground vibrational state of PH3, on the basis of their calculated inversion barrier of 6000 cm . However, subsequent quantum chemical calculations have predicted [see a much higher barrier (between 10 000 and 14 000 cm ). A molecular-beam electric resonance spectrometer has been used to measure the ground state inversion splitting in PH3. It was found that the inversion splitting must be lower than the resolution of the spectrometer (1 kHz). Similarly, in a hi -resolution infrared study of the 41 2 band of PH3, Maki et aL found that the splitting of this level must be less than 0.02 cm". ... 

The second approach to the study of reactive scattering involves the use of some spectroscopic method for the detection of the products in specified internal quantum states. Molecular spectroscopy is well suited to the determination of the relative populations in individual states since the quantum numbers of the upper and lower states of a molecular line in an assigned transition are known. Moreover, the intensities may be directly related to concentrations of specific internal states. The original implementation of this approach for the study of reactive scattering involved observation of spontaneous infrared emission from the radiative decay of vibrationally excited products [4, 5]. This approach is still being employed, however now usually with detection of the emission with Fourier transform [6], rather than grating-tuned spectrometers. In some cases, emission from electronically excited products can be observed for highly exothermic reactions. 

Why do we use Raman spectroscopy Competing methods for studying vibrational states of molecules include infrared (IR) spectroscopy (see Chapter 8) and fluorescence spectroscopy, both of which are guided by the electric dipole selection rules described in this chapter. While Raman selection rules do offer access to many quantum states that are forbidden to IR spectrometers, the ongoing development of Raman-based technology is actually driven by other needs. 

SYu Volkov, DN Kozlov, PV Nikles, AM Prokhorov, VV Smirnov, SM Chuksin. Infrared-CARS spectrometer with 0.001 cm resolution in the 1900-5000 cm range. Sov J Quantum Electron 11 135-137, 1981. 

Nelson D. D., Shorter J. H., McManus J. B., and Zahniser M. S., Sub-part-per-billion detection of nitric oxide in air using a thermoelectrically cooled mid-infrared quantum cascade laser spectrometer, Appl. Phys. B Lasers Opt, 75, 343-350 (2002). 

Ma, B. and Sun, Y.-R, Fluorescence spectra and quantum yields of [60]fullerene and [70]fiillerene under different solvent conditions. A quantitative examination using a near-infrared-sensitive emission spectrometer, /. Chem. Soc., Perkin Trans. 2, 2157,1996. 

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