For the first vowel in
I chose to use the symbol /3/.
The real IPA symbol for this is a turned Greek epsilon,
Unicode symbol hexadecimal 025C. It denotes a lower-mid central unrounded vowel.
Other sources, such as XSAMPA and Teach Yourself Books, use /6/ for this, a turned a, Unicode symbol hex 0250. This is a low central unrounded vowel.
Of course, the difference is small, and the actual sound varies. Still, I think using /6/ for what I call /3/ places this vowel too much in the vicinity of /a/. It seems more likely that a language maintains a certain distance between its vowels, so they can be distinguished easier. See also the Vowel diagram for relative positions.
Using /3/ suggests that the sound should resemble the vowel in British English, especially northern varieties thereof, in words like "bird". Cf. the first vowel in catedral © with the sound of "ur" in pretty nurses, from the famous Beatle song "Penny Lane".
The first a in catedral is normally unstressed, but the metrics of this song give it a secondary stress, which makes it much easier to hear the actual vowel sound.