Table 3.

XPS C(1s)/N(1s) for A, C, G, T, and U from ref. 16 and from formamide at 84 K (condensed phase) and higher temperatures

A* C* G* T* T U* 84 K 300 K 450 K 600 K 700 K
1.1 1.6 1.1 2.8 2.4 2.1 1.1 1.2 1.1 1.6 1.5
1.0§ 1.33§ 1.0§ 2.5§ 2.5 2§ 1.0§
  • Shown are the expected theoretical ratios from the chemical formulae.

  • * From ref. 16.

  • Calculated from a fresh thymine sample analyzed using a Phi XPS double-pass CMA machine. Correction factors were as follows: C, 0.296; O, 0.711; and N, 0.477 [from Phi Handbook (22)].

  • From Fig. 2.

  • § Theoretical ratios.