TABLE I.

Electronic excited states of cytosine from ab initio calculations, electron energy loss (EEL) spectroscopy in the gas phase and vacuum ultraviolet spectroscopy (VUV) of sublimed films compared to EEL spectroscopy of cytosine deposited on an inert argon substrate. I₁, I₂, I₃, and I₄, represent the vertical ionization energies of the molecule. Values within parentheses are the FWHM of the excitation bands. All energies are in eV.

Theory					EEL		VUV
State	CC2a	DFTb	CASPT2c	DFTd	Gase	Filmf	Filmg	Filmh
1 3A′ (π → π*)	3.88			3.60	3.50	3.55 (0.37)
2 3A′ (π → π*)	4.71				4.25	4.02 (0.51)
2 1A′ (π → π*)	4.66	4.83	4.39		4.65	4.65 (0.68)	4.54 (0.60)	4.50
1 3A″ (n → π*)	4.79
1 1A″ (n → π*)	4.87	5.02	5.00			5.01 (0.15)
2 3A″ (n → π*)	5.09
2 1A″ (n → π*)	5.26	5.50	6.53
3 3A′ (π → π*)	5.27
3 1A′ (π → π*)	5.62	5.67	5.36		5.50	5.39 (0.81)	5.40 (0.87)
3 3A″ (n → π*)	5.67
3 1A″ (n → π*)	5.84	5.91
4 1A′ (π → π*)		6.60	6.16		6.20	6.18 (1.04)	6.07 (0.79)	6.18
5 1A′ (π → π*)			6.74		6.70	6.83 (0.73)	6.67 (0.79)
6 1A′ (π → π*)			7.61		8.00	7.55 (1.30)	7.35 (0.79)	7.5
I1						8.55 (1.18)		8.5
I2						9.21 (0.83)
I3						9.83 (0.93)
I4						11.53(3.91)

^aCalculated results from Reference 51.

^bCalculated results from Reference 50.

^cCalculated results from Reference 52.

^dCalculated results from Reference 59.

^eReference 24

^fThis work.

^gReference 53.

^hReference 54