Rotational Spectrum of CO

FIGURE 13 4 The pure rotational spectrum for C O synthesized from data at the HTTRAN site using Spectralcalc software at http //www.spectralcalc.com/calc/spectralcalc.php (From Dr. Keeyoon Sung of the CalTech/Jet Propulsion Laboratory.) 

8626 cm averaged over 16 peaks [13]. For perspective, note that the main absorption peaks are around 50 and that = /tv = = hcv. Then given the Rydberg constant for the H atom as 

Using [A(A )J eliminates the need to know the actual j value and we only need to know the difference between the corresponding frequencies (vy+i — v ) = 

Consultation with several molecular spectroscopists reveals that modern Fourier transform infrared spectrometers are so precise that they usually measure only one or two rotational lines at a time with very high resolution and save the data in a computer file in a data bank such as the HITRAN site [15]. Then at a later time they use a computer program to splice together the various files to make a complete spectmm. The above-mentioned spectrum for CO was constmcted in such a manner. 

---

There is no observation of the pure rotational spectrum of CO, although it should be measurable and would provide rotation temperatureswhich could be compared with vibration temperatures and confirm the LTE population of CO levels. 

Another publication considered the rotational spectrum of CO solvated in para — (H2)a/ clusters, for cluster sizes (N) 2-17 [46]. Here R 0) transitions and their spectral weights were assigned up to A = 9 for -type series (free molecule rotations) and A = 14 for a-type series (end-over-end rotations). As was the case for CO-Hejv, there was a decreasing tendency of the hydrogen molecules to dynamically cluster on one side of the CO molecular axis as completion of the first solvation shell was approached. Theory and experiment agreed well, except that theory tended to overestimate the -type energies. 

Figure 6.9 The 1-0 Stokes vibrational Raman spectrum of CO showing the 0-, Q-, and 5-branch rotational structure...

Let us consider the quasi-classical formulation of impact theory. A rotational spectrum of ifth order at every value of co is a sum of spectral densities at a given frequency of all J-components of all branches... 

Looney J. P., Rosasco G. J., Rahn L. A., Hurst W. S., Hahn J. W. Comparison of rotational relaxation rate laws to characterize the Raman Q-branch spectrum of CO at 295 K, Chem. Phys. Lett. 161, 232-8 (1989). 

Figure 4.22. The infrared spectrum of gas phase CO shows rotational fine structure, which disappears upon adsorption, as shown by the spectrum of CO adsorbed on an Ir/Si02 catalyst. [J.W. Niemantsverdriet, Spectroscopy in Catalysis, An Introduction (2000), Wiley-VCH, Weinheim.]...

Figure 3.7 Simulated spectrum of CO with a rotational temperature of 40 K. Reproduced by with permission of Albert Nummelin, Chalmers University of Technology...

Anharmonic Force Constant Refinements.—The preceding parts of this Section 4 constitute an outline of how the vibration-rotation spectrum of a molecule may be calculated from a knowledge of the force field in some set of geometrically defined internal co-ordinates, denoted V(r) in general in this Report [but denoted V(X) in the special discussion on pp. 126—132], In practice we wish to solve the reverse problem we observe the vibration-rotation spectra, and we wish to deduce the force field. 

Part of the high-resolution rotational-vibrational FTIR spectrum of CO(g), showing the P(<2140cm 1) and R (>2140 cm-1) bands, and the contributions from the C13 isotope [9],... 

Figure 9.31. FIR laser magnetic resonance spectrum of CO in the a 3n state, observed using the 393.6 pm line from formic acid [62]. This spectrum arises from the J = 7 — 6 rotational transition in the Q = 2 fine-structure state, and the transitions obey the selection rule A Mj = +1. The lower Mj states are indicated in the diagram.

It passes through the sample absorption cell made of Pyrex with polyethylene windows and is detected with a liquid helium cooled bolometer. One of the lasers is frequency-modulated at 1 kHz and the detector output is processed with a lock-in amplifier, as shown. Far-infrared rotational spectra of CO, HC1 and HF have been recorded [67], and as an example of the excellent sensitivity achieved, we refer the reader to the spectrum of the OH radical [68] shown later in this chapter. Evenson s spectrometer operates over a wide range of the far-infrared region up to 9 THz, with excellent frequency stability. 

Figure 4.3-3 Spectrum of CO with pressure of 54 hPa, temperature of 25 °C and optical pathlength of 10 cm at a spectral resolution of 0.05 cm the fundamental region is enlarged in the inset showing also the rotation-vibration features of the isotope (see also text).

Figure 6.3 Radiative decay rates (r = 1/t) for single e-parity rotational levels of CO A1 (v = 0). The effects of perturbations by e3E (v = 1) are evident near J = 9(1 1) and J = 16(F3). The points (O and S refer to branches in the two-photon spectrum) are measured and the solid curves depict values calculated for the nominal, A1] , e3 — (fb), and e3 —(F3) levels from the deperturbed t 0 = 9.9 ns of Field et at, (1983) and mixing coefficients from the deperturbation analysis (Field, 1971). [From Girard, et al., (1982).]...

Aside from the CO laser transitions, the absorption spectrum of CO has been more accurately and thoroughly measured than any other spectrum. A bibliography of earlier measurements on CO is given by Maki and Wells, and the present tables were calculated from the measurements referred to in that work. In addition, some new and very accurate frequency measurements have been made and were incorporated in the present tables. The frequencies of the rotational transitions of HF and HCl were calculated from constants obtained from fitting the measurements of Evenson et al. and Jennings and Wells. ... 

Many early infrared and Raman papers have reported studies on polar molecules which subsequently have been reexamined in the microwave region. In most of these cases, the microwave woik is clearly superior and the infrared results have not been included in these tables. In some cases, however, the addition of even relatively low precision optical data, when combined with microwave data, will lead to improved structural estimates. For example, frequently the Aq (or Co) rotational constant of a symmetric top can be obtained either from pertutbation-induced transitions in the infrared spectrum or from suitable combinations of transitions in a fundamental band, a combination band and a hot band, or else by the analysis of a perpendicular band in the Raman spectrum. It is not possible to obtain this rotational constant in the pure rotational spectrum of a symmetric top molecule, and therefore combining the optical and microwave data leads to much improvement in determining the positions of the off-axis atoms of such molecules. 

Figure 5.8. Pure rotational PARS spectrum of CO at 500 Torr [4],...

---