Hydrogen Spectrum
If an electric discharge is passed through hydrogen gas taken in a discharge tube under low pressure, and the emitted radiation is analyzed with the help of spectrograph, it is found to consist of a series of sharp lines in the UV, visible and IR regions. This series of lines is known as line or atomic spectrum of hydrogen. The lines in the visible region can be directly seen on the photographic film.
Each line of the spectrum corresponds to a light of definite
wavelength. The entire spectrum consists of six series of lines, each series,
known after their discoverer as the Balmer, Paschen, Lyman, Brackett, Pfund and
Humphrey series. The wavelength of all these series can be expressed by a
single formula.
1/ λ = v- = R (1/ n12 - 1/n22)
λ = wave
length
R = Rydberg
constant (109678 cm–1)
Note:
All lines in the visible region are of Balmer series but reverse is not true.
i.e., all Balmer lines will not fall in visible region. The pattern of lines in
atomic spectrum is characteristic of hydrogen.
LYMAN SERIES:
When an
electron jumps from any of the higher states to the ground state or Ist state
(n = 1), the series of spectral lines emitted lies in ultra-violet region and
are called as Lyman Series. The wavelength (or wave number) of any line of the
series can be given by using the relation:
BALMER SERIES:
When an
electron jumps from any of the higher states to the state with n = 2 (IInd state),
the series of spectral lines emitted lies in visible region and are called as Balmer
Series. The wave number of any spectral line can be given by using the relation:
PASCHEN SERIES:
When an electron jumps from any of the higher states to the
state with n = 3. The series of spectral lines emitted lies in near infra-red
region and are called as Paschen Series. The wave number of any spectral line
can be given by using the relation:
BRACKETT SERIES:
When an
electron jumps from any of the higher states to the state with n = 4, the
series of spectral lines emitted lies in far infra-red region and called as Brackett
Series. The wave number of any spectral line can be given by using the relation:
PFUND SERIES:
When an
electron jumps from any of the higher states to the state with n = 5 , the
series of spectral lines emitted lies in far infra-red region and are called
as Pfund
Series . The wave number of any spectral line can be given by using the relation:
