How to measure voltage across (pre-charged) capacitor using an MCU?
Your two 100 ohm divider resistors will in fact reduce the voltage of the 1 uF capacitor to 50% of its original value in 0.13 milliseconds. You likely will not be able to charge the cap and take the reading fast enough to make this an effective circuit.

To improve your measurement technique, keep each resistor at a value of about 1/10 of the input impedance of your ADC. So if your ADC input impedance is 100k, use 10k resistors. With these resistors, the capacitor will still be at 99% if its original voltage in the same 0.13 milliseconds later.

A formula that is helpful to know is the following:

VC = VS*e-t/RC

where VC is the voltage across the capacitor at time t, VS is the voltage to which the capacitor was initially charged, t is the time in seconds, R is the resistance in ohms, and C is the capacitance in farads.

From this you can calculate that if you charge the cap and then wait t seconds to take the reading, you know what voltage to expect across the cap. A simpler version of the formula tells you what % of charge remains on the cap after some time has passed:

% of original voltage = e-t/RC*100

And finally, a comment about your schematic. The bottom leg to which the ADC is connected (shown as ADC -) must be grounded unless you have a differential ADC on your uP, which is very rare.