HI! Since you did not mention where you want to opt for phd in astrochemistry, here is a list of the worlds top universities from where you can pursue you dreams:

university of sheffield, department of chemistry

leiden university faculty of science

california institute of technology

harvard university

university of california, berkeley

university of cambridge

princeton university

sorbonne universite

stanford university

university of chicago

university of toronto

massachusetts institute of technology

university of oxford

university of padua

johns hopkins university

university of geneva

yale university

columbia university