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.