7095
Here , we exploit the rapid T ( 1 ) relaxation of these materials to obtain ( 13 ) C NMR spectra using a spin - echo pulse sequence at natural abundance levels , and employ frequency - stepped acquisition to ensure uniform excitation of resonances over a wide frequency range .
 Chemical: ( 13 ) C
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: ( 13 ) C