Calculating Vapor Pressure Deficit in Excel (Problem with complex formula)

Hello excel geniuses!

I've run into a formula that I can't seem to get working correctly in Excel and I'm about at the end of my rope.

The formula I'm interested in is the first calculation for estimation of Vapor Pressure Deficit (important in Viticulture and botany in general).

The specific formula can be found under Step 2a in the attachment below. It's also located 3/4 of the way down the page here.

In the code below is the formula I've input into excel. C2 references a field that holds Ambient Temp in degrees F (in the formula it is converted to Kelvin). In the attachment below they give an example using 50F which gives a result of .178 psi.

=EXP(((-1.0440397*10^4)/(C2+459.67))+(-1.129465*10^1)+((-2.7022355*10^-2)*(C2+459.67))+((-1.289036*10^-5)*(C2*459.67)^2)+((-2.4780681*10^-9)*((C2+459.67)^3))+((-6.5459673)*LN(C2+459.67)))

My formula keeps generating a result of 0, and only 0 unfortunately. I've checked and compared the two formulas multiple times but can't find a typing error. I'm left thinking that my nesting of parenthesis are off or that I'm not formating the exp() or ln() functions correctly somehow.

I really appreciate any help or advice anyone can give!

Josh