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Vacuum and Q-mass Measurement Data

Interpretation of Mass peak

The following list shows the name and description of the gas corresponding to each mass number observable when residual gas is analyzed for mass peak (mass spectrum).

List of residual gas spectra

Mass number	Ion	Description	Mass number	Ion	Description
1	H+	H2, H2O, HC, etc	30	NO+	Found immediately after evacuation of a dirty evacuation system
2	H2+	H2, H2O, HC, etc	31	CH3O+	alcohol
3	HD+	Abundance ratio of D about 0.01%	32	O2+	N23:O32 = 4:1 when air leak occurs.
4	He+		35	Cl+
12	C+	CO, CO2, HC	37	Cl+	Cl35:Cl37 = 3:1
14	N+, CH2+, CO2+	N2, CO, HC	39	K+, C3H3+	K+ dissociated from filament
15	CH3+	Molecules with CH4 or CH3	40	Ar+, C3H4+	Ar is present in the atmosphere at 1%.
16	C+, CH4+	O2, CH4, oxygen compound	41	C3H5+	HC
17	OH+	H2O	42	C3H6+	HC
18	H2O+	H2O, OH+ : H2O+ ≈ 1 : 5	43	C3H7+	HC
19	F+	May be adsorbed to filaments and electrode surfaces.	44	CO2+
20	Ar+, H2O+, Ne+	H2O (20) having an O 15 abundance ratio of about 0.2%	50	C4H2+	HC
22	CO22+, Ne+	Abundance ratio of Ne22: 8.8%	51	C4H3+	HC
23	Na+	May be adsorbed to filaments and electrode surfaces.	55	C4H7+	HC
27	C2H3+	HC	56	C4H8+	HC
28	N2+, CO+	Present at all times	57	C4H9+	HC
29	C2H5+, N2+, CO+	Abundance ratio of N15 : 0.7%, abundance ratio of C13 : 1.1%

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