Isotopes methanes

Composition of isotopic methanes resulting from sequential pulses of C32H8 and Cj1 over freshly reduced Pt/aJumma samples at 773 and 873 K ... 

An alternative scheme which accounts for the isotopic methanes is... 

It is to be noted carefully that quite often one is faced with a condensed phase molecule where some of the frequencies fit neatly into neither the A nor the B class. In such an event any meaningful calculations should employ the complete equation, at least if the particular frequency or frequencies are strongly isotope dependent. Nonetheless, Equation 3 is still useful even in such cases because it is more readily associated with a physical picture of the condensation process. Often an approximate forcing of the data into T and T terms facilitates the selection of approximate parameters to be employed in calculations using the complete Equation 2. These parameters are then subject to later refinement. Such a technique is described below and in Reference 37 where the theory is applied to chromatographic data for the isotopic methanes. 

Table II. Separation of Isotopic Methanes on a Charcoal Column ...

MOLECULAR ENERGY STATES AND THE THERMODYNAMIC PROPERTIES OF SOLID ISOTOPIC METHANES. 

Figure 5. Vapor pressures of the isotopic methanes (41).---------ft to data ------calculated from Table 2 (5).

The isotope effect studies of the oxidation of aliphatic chains will be covered by us more extensively in a chapter in Supplement B2 of this series and tritium isotope effects in the oxidation of isotopic methanes over CuO to carbon dioxide and water have shown that the C—H bond rupture is the rate-determining step in this process, average k iiQuJkisQ, — 1.0074 t 0.(X)10 at 700 C, average k cu4)/ (CH3 H) 1.18 0.05, (c—H)/ (c—T) = 7(X)-750 °C neglecting secondary tritium isotope effects... 

A mixture of 70% N2 and 30% He was employed as carrier gas. This mixture is recommended because use of helium alone at liquid nitrogen temperature causes a very strong retention of methane. With this mixture some nitrogen is adsorbed on the silica layer of the column. At values of the relative vapor pressures p/pjj between 0.7-0.9 a polymolecular layer of Ng covers all the surface, and pores with a radius below 80 A are filled. In this way the most active sites of the adsorbent, which are located in the small pores, are blocked, and as a consequence retention volumes are decreased and symmetrical peaks are obtained. Separation of all isotopic methanes obtained on the glass capillary column at liquid nitrogen temperature is shown in Fig. 6-21 [90]. In the upper part of the chromatogram there are the radioactive compounds detected by the ion chamber and in the lower part there are the stable isotopes monitored by the flame ionization detector. These chromatograms do not refer to the seime injection. 

In the case of isotopic methanes, we would expect from (V-37) that the vapor pressure of CH should be higher than that of CD4 owing to the fact that Mch, < Mcd, and Ach. < Acd.-... 

L. H. Jones and R. S. McDowell, Force Constants of Methane. Infrared Spectra and Thermodynamic Functions of Isotopic Methanes, J. Mol. Spectroscopy 3, 632-653, 1959 cf. CA 52,11568c. 

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